{"id":80847,"date":"2024-11-12T09:08:41","date_gmt":"2024-11-12T02:08:41","guid":{"rendered":"https:\/\/itviec.com\/blog\/?p=80847"},"modified":"2024-11-12T09:08:41","modified_gmt":"2024-11-12T02:08:41","slug":"index-trong-database","status":"publish","type":"post","link":"https:\/\/itviec.com\/blog\/index-trong-database\/","title":{"rendered":"Index trong database: H\u01b0\u1edbng d\u1eabn c\u00e1ch s\u1eed d\u1ee5ng chi ti\u1ebft"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_85 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">N\u1ed9i dung b\u00e0i vi\u1ebft<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/#Index_trong_database_la_gi\" >Index trong database l\u00e0 g\u00ec?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/#Phan_loai_index_trong_database_theo_muc_dich_su_dung\" >Ph\u00e2n lo\u1ea1i index trong database theo m\u1ee5c \u0111\u00edch s\u1eed d\u1ee5ng\u00a0<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/#Phan_loai_index_trong_database_theo_cau_truc\" >Ph\u00e2n lo\u1ea1i index trong database theo c\u1ea5u tr\u00fac<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/#Phan_loai_index_trong_database_theo_phuong_thuc_quan_ly\" >Ph\u00e2n lo\u1ea1i index trong database theo ph\u01b0\u01a1ng th\u1ee9c qu\u1ea3n l\u00fd<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/#Mot_so_thao_tac_voi_index_trong_database\" >M\u1ed9t s\u1ed1 thao t\u00e1c v\u1edbi index trong database<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/#Mot_so_quy_tac_chon_index_index_trong_database_phu_hop\" >M\u1ed9t s\u1ed1 quy t\u1eafc ch\u1ecdn index index trong database ph\u00f9 h\u1ee3p<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/#Uu_diem_cua_index_trong_database\" >\u01afu \u0111i\u1ec3m c\u1ee7a index trong database<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/#Nhuoc_diem_cua_index_trong_database\" >Nh\u01b0\u1ee3c \u0111i\u1ec3m c\u1ee7a index trong database<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/#Tong_ket_index_trong_database\" >T\u1ed5ng k\u1ebft index trong database<\/a><\/li><\/ul><\/nav><\/div>\n<p><em><strong>Hi\u1ec7u su\u1ea5t l\u00e0 m\u1ed9t y\u1ebfu t\u1ed1 c\u1ed1t l\u00f5i trong vi\u1ec7c x\u00e2y d\u1ef1ng c\u00e1c \u1ee9ng d\u1ee5ng ch\u1ea5t l\u01b0\u1ee3ng cao. M\u1ed9t trong nh\u1eefng kh\u00eda c\u1ea1nh quan tr\u1ecdng c\u1ee7a hi\u1ec7u su\u1ea5t ch\u00ednh l\u00e0 t\u1ed1c \u0111\u1ed9 truy xu\u1ea5t d\u1eef li\u1ec7u m\u00e0 \u1ee9ng d\u1ee5ng c\u1ea7n \u0111\u1ec3 ho\u1ea1t \u0111\u1ed9ng hi\u1ec7u qu\u1ea3. B\u00ean c\u1ea1nh vi\u1ec7c t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n v\u00e0 b\u1ed9 nh\u1edb \u0111\u1ec7m, vi\u1ec7c tri\u1ec3n khai v\u00e0 s\u1eed d\u1ee5ng index c\u0169ng l\u00e0 \u01b0u ti\u00ean h\u00e0ng \u0111\u1ea7u c\u1ee7a c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n khi x\u00e2y d\u1ef1ng c\u00e1c \u1ee9ng d\u1ee5ng c\u00f3 kh\u1ea3 n\u0103ng truy xu\u1ea5t d\u1eef li\u1ec7u nhanh ch\u00f3ng. Do \u0111\u00f3, vi\u1ec7c hi\u1ec3u v\u00e0 s\u1eed d\u1ee5ng \u0111\u00fang index trong database l\u00e0 c\u1ea7n thi\u1ebft \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o hi\u1ec7u su\u1ea5t t\u1ed1i \u01b0u cho h\u1ec7 th\u1ed1ng.<\/strong><\/em><\/p>\n<p><span style=\"font-weight: 400;\">\u0110\u1ecdc b\u00e0i vi\u1ebft sau \u0111\u1ec3 hi\u1ec3u th\u00eam v\u1ec1:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">C\u00e1c lo\u1ea1i index trong database<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">M\u1ed9t s\u1ed1 c\u1ea5u tr\u00fac index ph\u1ed5 bi\u1ebfn<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">M\u1ed9t s\u1ed1 thao t\u00e1c v\u1edbi index<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">\u01afu &#8211; nh\u01b0\u1ee3c \u0111i\u1ec3m c\u1ee7a index<\/span><\/li>\n<\/ul>\n<h2><span class=\"ez-toc-section\" id=\"Index_trong_database_la_gi\"><\/span><b>Index trong database l\u00e0 g\u00ec?<\/b><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><span style=\"font-weight: 400;\">Index trong database l\u00e0 m\u1ed9t c\u1ea5u tr\u00fac d\u1eef li\u1ec7u \u0111\u1eb7c bi\u1ec7t gi\u00fap t\u0103ng t\u1ed1c \u0111\u1ed9 truy xu\u1ea5t d\u1eef li\u1ec7u t\u1eeb c\u00e1c b\u1ea3ng b\u1eb1ng c\u00e1ch cung c\u1ea5p m\u1ed9t c\u00e1ch nhanh ch\u00f3ng nh\u1eefng \u0111i\u1ec1u ki\u1ec7n t\u00ecm ki\u1ebfm h\u00e0ng d\u1ef1a tr\u00ean gi\u00e1 tr\u1ecb c\u1ee7a m\u1ed9t ho\u1eb7c nhi\u1ec1u c\u1ed9t.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">N\u00f3 ho\u1ea1t \u0111\u1ed9ng gi\u1ed1ng nh\u01b0 m\u1ee5c l\u1ee5c c\u1ee7a m\u1ed9t cu\u1ed1n s\u00e1ch, gi\u00fap b\u1ea1n t\u00ecm ki\u1ebfm th\u00f4ng tin nhanh ch\u00f3ng m\u00e0 kh\u00f4ng c\u1ea7n ph\u1ea3i duy\u1ec7t qua to\u00e0n b\u1ed9 n\u1ed9i dung. Khi s\u1eed d\u1ee5ng index, c\u01a1 s\u1edf d\u1eef li\u1ec7u c\u00f3 th\u1ec3 t\u00ecm ki\u1ebfm, truy v\u1ea5n v\u00e0 l\u1ea5y d\u1eef li\u1ec7u t\u1eeb c\u00e1c b\u1ea3ng m\u1ed9t c\u00e1ch nhanh h\u01a1n nhi\u1ec1u.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 ta c\u00f3 b\u1ea3ng Students v\u1edbi c\u00e1c thu\u1ed9c t\u00ednh nh\u01b0 ID, Name, Age nh\u01b0 sau:<\/span><\/p>\n<table>\n<tbody>\n<tr>\n<td><b>ID<\/b><\/td>\n<td><b>Name<\/b><\/td>\n<td><b>Age<\/b><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400;\">1<\/span><\/td>\n<td><span style=\"font-weight: 400;\">John<\/span><\/td>\n<td><span style=\"font-weight: 400;\">20<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400;\">2<\/span><\/td>\n<td><span style=\"font-weight: 400;\">Mary<\/span><\/td>\n<td><span style=\"font-weight: 400;\">22<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400;\">3<\/span><\/td>\n<td><span style=\"font-weight: 400;\">John<\/span><\/td>\n<td><span style=\"font-weight: 400;\">21<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400;\">4<\/span><\/td>\n<td><span style=\"font-weight: 400;\">Anna<\/span><\/td>\n<td><span style=\"font-weight: 400;\">19<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><span style=\"font-weight: 400;\">Gi\u1ea3 s\u1eed b\u1ea1n mu\u1ed1n t\u00ecm t\u1ea5t c\u1ea3 c\u00e1c sinh vi\u00ean c\u00f3 t\u00ean l\u00e0 &#8220;John&#8221;, c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd ph\u1ea3i qu\u00e9t to\u00e0n b\u1ed9 b\u1ea3ng \u0111\u1ec3 t\u00ecm k\u1ebft qu\u1ea3. Tuy nhi\u00ean, n\u1ebfu b\u1ea1n t\u1ea1o m\u1ed9t index tr\u00ean c\u1ed9t <\/span><i><span style=\"font-weight: 400;\">Name<\/span><\/i><span style=\"font-weight: 400;\">, vi\u1ec7c t\u00ecm ki\u1ebfm n\u00e0y s\u1ebd tr\u1edf n\u00ean nhanh h\u01a1n nhi\u1ec1u v\u00ec database ch\u1ec9 c\u1ea7n tham chi\u1ebfu tr\u1ef1c ti\u1ebfp \u0111\u1ebfn v\u1ecb tr\u00ed c\u1ee7a c\u00e1c b\u1ea3n ghi c\u00f3 t\u00ean &#8220;John&#8221; thay v\u00ec qu\u00e9t c\u1ea3 b\u1ea3ng.\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400;\">\u0110\u1ec3 minh h\u1ecda r\u00f5 r\u00e0ng h\u01a1n, b\u1ea1n c\u00f3 th\u1ec3 t\u01b0\u1edfng t\u01b0\u1ee3ng index gi\u1ed1ng nh\u01b0 m\u1ed9t danh s\u00e1ch ch\u1ec9 m\u1ee5c s\u1eafp x\u1ebfp c\u00e1c gi\u00e1 tr\u1ecb c\u1ee7a c\u1ed9t <\/span><b>Name<\/b><span style=\"font-weight: 400;\"> (John, Mary, Anna) k\u00e8m theo v\u1ecb tr\u00ed c\u1ee7a ch\u00fang trong b\u1ea3ng nh\u01b0 sau:<\/span><\/p>\n<table>\n<tbody>\n<tr>\n<td><\/td>\n<td><b>Name<\/b><\/td>\n<td><b>Pointer (ID)<\/b><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400;\">1<\/span><\/td>\n<td><span style=\"font-weight: 400;\">Anna<\/span><\/td>\n<td><span style=\"font-weight: 400;\">4<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400;\">2<\/span><\/td>\n<td><span style=\"font-weight: 400;\">John<\/span><\/td>\n<td><span style=\"font-weight: 400;\">1<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400;\">3<\/span><\/td>\n<td><span style=\"font-weight: 400;\">John<\/span><\/td>\n<td><span style=\"font-weight: 400;\">3<\/span><\/td>\n<\/tr>\n<tr>\n<td><span style=\"font-weight: 400;\">4<\/span><\/td>\n<td><span style=\"font-weight: 400;\">Mary<\/span><\/td>\n<td><span style=\"font-weight: 400;\">2<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><span style=\"font-weight: 400;\">Trong h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u, Index \u0111\u00f3ng vai tr\u00f2 r\u1ea5t quan tr\u1ecdng trong vi\u1ec7c t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n, gi\u00fap t\u0103ng t\u1ed1c \u0111\u1ed9 t\u00ecm ki\u1ebfm v\u00e0 truy xu\u1ea5t d\u1eef li\u1ec7u. Tuy nhi\u00ean index c\u00f3 r\u1ea5t nhi\u1ec1u lo\u1ea1i kh\u00e1c nhau d\u1ef1a tr\u00ean m\u1ee5c \u0111\u00edch s\u1eed d\u1ee5ng, c\u1ea5u tr\u00fac v\u00e0 ph\u01b0\u01a1ng th\u1ee9c qu\u1ea3n l\u00fd. D\u01b0\u1edbi \u0111\u00e2y l\u00e0 ph\u00e2n lo\u1ea1i chi ti\u1ebft v\u1ec1 c\u00e1c lo\u1ea1i Index trong c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/span><\/p>\n<blockquote><p><em>\u0110\u1ecdc th\u00eam: <a href=\"https:\/\/itviec.com\/blog\/database-schema-luoc-do-co-so-du-lieu\/\" target=\"_blank\" rel=\"noopener\"><strong>Database schema l\u00e0 g\u00ec? C\u00e1ch t\u1ed5 ch\u1ee9c l\u01b0\u1ee3c \u0111\u1ed3 c\u01a1 s\u1edf d\u1eef li\u1ec7u t\u1ed1i \u01b0u<\/strong><\/a><\/em><\/p><\/blockquote>\n<h2><span class=\"ez-toc-section\" id=\"Phan_loai_index_trong_database_theo_muc_dich_su_dung\"><\/span><b>Ph\u00e2n lo\u1ea1i index trong database theo m\u1ee5c \u0111\u00edch s\u1eed d\u1ee5ng\u00a0<\/b><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<h3><b>Clustered Index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Clustered Index s\u1eafp x\u1ebfp d\u1eef li\u1ec7u v\u1eadt l\u00fd trong b\u1ea3ng theo th\u1ee9 t\u1ef1 c\u1ee7a gi\u00e1 tr\u1ecb c\u1ed9t \u0111\u01b0\u1ee3c ch\u1ec9 \u0111\u1ecbnh l\u00e0m index. D\u1eef li\u1ec7u \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef trong c\u00e1c n\u00fat l\u00e1 c\u1ee7a c\u00e2y B+ (B+ tree).<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-81135\" src=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-vippro.jpg\" alt=\"clustered index - index trong database - itviec blog\" width=\"1636\" height=\"492\" srcset=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-vippro.jpg 1636w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-vippro-300x90.jpg 300w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-vippro-1600x481.jpg 640w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-vippro-200x60.jpg 200w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-vippro-100x30.jpg 100w\" sizes=\"auto, (max-width: 1636px) 100vw, 1636px\" \/><\/p>\n<p><span style=\"font-weight: 400;\">H\u00ecnh tr\u00ean cho th\u1ea5y c\u00e1ch m\u1ed9t Clustered Index s\u1eafp x\u1ebfp d\u1eef li\u1ec7u d\u1ef1a tr\u00ean c\u1ed9t ID. C\u00e1c b\u1ea3n ghi \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef trong c\u00e1c n\u00fat l\u00e1 c\u1ee7a B+ tree v\u00e0 m\u1ed7i n\u00fat l\u00e1 ch\u1ee9a to\u00e0n b\u1ed9 b\u1ea3n ghi d\u1eef li\u1ec7u. Tuy nhi\u00ean n\u1ebfu th\u00eam m\u1ed9t b\u1ea3n ghi m\u1edbi c\u00f3 ID = 16, B+ tree s\u1ebd t\u1ef1 \u0111\u1ed9ng c\u00e2n b\u1eb1ng l\u1ea1i \u0111\u1ec3 ph\u00f9 h\u1ee3p v\u1edbi b\u1ea3n ghi m\u1edbi nh\u01b0 sau:<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-81134\" src=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-2-vippro.jpg\" alt=\"clustered index - index trong database - itviec blog\" width=\"1728\" height=\"646\" srcset=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-2-vippro.jpg 1728w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-2-vippro-300x112.jpg 300w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-2-vippro-1600x598.jpg 640w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-2-vippro-200x75.jpg 200w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/clustered-index-trong-database-2-vippro-100x37.jpg 100w\" sizes=\"auto, (max-width: 1728px) 100vw, 1728px\" \/><\/p>\n<p><span style=\"font-weight: 400;\">C\u00f3 th\u1ec3 th\u1ea5y s\u1ef1 thay \u0111\u1ed5i c\u1ea5u tr\u00fac B+ tree sau khi th\u00eam b\u1ea3n ghi v\u1edbi ID = 16. N\u00f3 b\u1eaft \u0111\u1ea7u b\u1eb1ng c\u00e1ch truy xu\u1ea5t c\u00e1c trang ch\u1ec9 m\u1ee5c c\u00f3 li\u00ean quan, sau \u0111\u00f3 ti\u1ebfn h\u00e0nh t\u00e1i c\u1ea5u tr\u00fac B+ tree \u0111\u1ec3 ch\u1ee9a b\u1ea3n ghi m\u1edbi. Khi qu\u00e1 tr\u00ecnh t\u00e1i c\u1ea5u tr\u00fac ho\u00e0n t\u1ea5t, c\u00f4ng c\u1ee5 s\u1ebd l\u01b0u c\u00e1c trang (page) \u0111\u00e3 c\u1eadp nh\u1eadt v\u00e0 ghi ch\u00fang tr\u1edf l\u1ea1i b\u1ed9 nh\u1edb, \u0111\u1ea3m b\u1ea3o r\u1eb1ng c\u00e2y B+ v\u1eabn \u1edf tr\u1ea1ng th\u00e1i \u0111\u01b0\u1ee3c t\u1ed1i \u01b0u h\u00f3a. Tuy nhi\u00ean c\u1ea7n l\u01b0u \u00fd l\u00e0 m\u1ed7i b\u1ea3ng ch\u1ec9 c\u00f3 th\u1ec3 c\u00f3 m\u1ed9t clustered index.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Clustered Index th\u00edch h\u1ee3p cho c\u00e1c b\u1ea3ng m\u00e0 b\u1ea1n th\u01b0\u1eddng th\u1ef1c hi\u1ec7n truy v\u1ea5n v\u1edbi \u0111i\u1ec1u ki\u1ec7n ph\u1ea1m vi (v\u00ed d\u1ee5: truy v\u1ea5n t\u1ea5t c\u1ea3 c\u00e1c b\u1ea3n ghi gi\u1eefa hai gi\u00e1 tr\u1ecb). V\u00ed d\u1ee5 \u0111i\u1ec3n h\u00ecnh l\u00e0 khi b\u1ea1n c\u00f3 m\u1ed9t b\u1ea3ng giao d\u1ecbch v\u00e0 c\u1ea7n truy xu\u1ea5t t\u1ea5t c\u1ea3 giao d\u1ecbch trong kho\u1ea3ng th\u1eddi gian nh\u1ea5t \u0111\u1ecbnh d\u1ef1a tr\u00ean c\u1ed9t <\/span><span style=\"font-weight: 400;\">transaction_date<\/span><span style=\"font-weight: 400;\">. Clustered Index gi\u00fap t\u1ed1i \u01b0u h\u00f3a c\u00e1c truy v\u1ea5n t\u00ecm ki\u1ebfm theo th\u1ee9 t\u1ef1 th\u1eddi gian.<\/span><\/p>\n<h3><b>Non-Clustered Index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Kh\u00f4ng gi\u1ed1ng nh\u01b0 Clustered Index, Non-Clustered Index kh\u00f4ng s\u1eafp x\u1ebfp d\u1eef li\u1ec7u theo h\u01b0\u1edbng v\u1eadt l\u00fd\u00a0 trong b\u1ea3ng. Thay v\u00e0o \u0111\u00f3, c\u00e1c n\u00fat l\u00e1 ch\u1ec9 ch\u1ee9a c\u00e1c con tr\u1ecf ho\u1eb7c ID tr\u1ecf t\u1edbi v\u1ecb tr\u00ed c\u1ee7a b\u1ea3n ghi d\u1eef li\u1ec7u th\u1ef1c t\u1ebf. C\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd x\u00e2y d\u1ef1ng m\u1ed9t B+ tree v\u1edbi c\u00e1c gi\u00e1 tr\u1ecb c\u1ee7a c\u1ed9t \u0111\u01b0\u1ee3c index l\u00e0m kh\u00f3a, nh\u01b0ng b\u1ea3n th\u00e2n d\u1eef li\u1ec7u kh\u00f4ng \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef trong c\u00e1c n\u00fat l\u00e1.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-81133\" src=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-vippro.jpg\" alt=\"non clustered index - index trong database - itviec blog\" width=\"1726\" height=\"702\" srcset=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-vippro.jpg 1726w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-vippro-300x122.jpg 300w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-vippro-1600x651.jpg 640w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-vippro-200x81.jpg 200w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-vippro-100x41.jpg 100w\" sizes=\"auto, (max-width: 1726px) 100vw, 1726px\" \/><\/p>\n<p><span style=\"font-weight: 400;\">H\u00ecnh tr\u00ean cho th\u1ea5y c\u00e1ch s\u1eed d\u1ee5ng Non-clustered index v\u1edbi c\u1ed9t email l\u00e0m kho\u00e1. C\u00f3 th\u1ec3 th\u1ea5y c\u00e1ch t\u1ed5 ch\u1ee9c d\u1eef li\u1ec7u kh\u00e1 gi\u1ed1ng v\u1edbi Clustered index nh\u01b0ng kh\u00e1c bi\u1ec7t \u1edf ch\u1ed7 c\u00e1c b\u1ea3n ghi kh\u00f4ng \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef trong c\u00e1c n\u00fat l\u00e1 \u1edf Non-clustered index. Thay v\u00e0o \u0111\u00f3, c\u00e1c n\u00fat l\u00e1 ch\u1ec9 ch\u1ee9a ID ho\u1eb7c v\u1ecb tr\u00ed c\u1ee7a b\u1ea3n ghi trong b\u1ed9 nh\u1edb, t\u00f9y thu\u1ed9c v\u00e0o c\u01a1 s\u1edf d\u1eef li\u1ec7u. Ph\u1ea7n l\u1edbn c\u00e1c h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1eed d\u1ee5ng ID c\u1ee7a b\u1ea3n ghi l\u00e0m gi\u00e1 tr\u1ecb trong c\u00e1c n\u00fat l\u00e1 nh\u01b0ng PostgreSQL s\u1ebd s\u1eed d\u1ee5ng v\u1ecb tr\u00ed (location) c\u1ee7a b\u1ea3n ghi trong b\u1ed9 nh\u1edb.\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400;\">N\u1ebfu th\u00eam m\u1ed9t b\u1ea3n ghi m\u1edbi c\u00f3 ID l\u00e0 16 v\u00e0o B+ tree, c\u1ea5u tr\u00fac s\u1ebd thay \u0111\u1ed5i nh\u01b0 sau:<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-81132\" src=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-2-vippro.jpg\" alt=\"non clustered index - index trong database - itviec blog\" width=\"1664\" height=\"656\" srcset=\"https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-2-vippro.jpg 1664w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-2-vippro-300x118.jpg 300w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-2-vippro-1600x631.jpg 640w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-2-vippro-200x79.jpg 200w, https:\/\/itviec.com\/blog\/wp-content\/uploads\/2024\/10\/non-clustered-index-trong-database-2-vippro-100x39.jpg 100w\" sizes=\"auto, (max-width: 1664px) 100vw, 1664px\" \/><\/p>\n<p><span style=\"font-weight: 400;\">C\u00f3 th\u1ec3 th\u1ea5y m\u1ed7i khi ch\u00fang ta th\u1ef1c hi\u1ec7n c\u00e1c thao t\u00e1c nh\u01b0 ch\u00e8n, c\u1eadp nh\u1eadt ho\u1eb7c x\u00f3a, h\u1ec7 th\u1ed1ng s\u1ebd th\u1ef1c hi\u1ec7n m\u1ed9t lo\u1ea1t c\u00e1c ho\u1ea1t \u0111\u1ed9ng nh\u01b0 truy xu\u1ea5t c\u00e1c trang ch\u1ec9 m\u1ee5c c\u00f3 li\u00ean quan, sau \u0111\u00f3 ti\u1ebfn h\u00e0nh t\u00e1i c\u1ea5u tr\u00fac c\u00e2y B+ \u0111\u1ec3 ch\u1ee9a b\u1ea3n ghi m\u1edbi. Sau khi qu\u00e1 tr\u00ecnh t\u00e1i c\u1ea5u tr\u00fac ho\u00e0n t\u1ea5t, c\u00f4ng c\u1ee5 s\u1ebd l\u01b0u c\u00e1c trang \u0111\u00e3 c\u1eadp nh\u1eadt c\u00e1c n\u00fat l\u00e1 b\u1eb1ng c\u00e1ch th\u00eam th\u00f4ng tin v\u1ec1 ID ho\u1eb7c v\u1ecb tr\u00ed c\u1ee7a b\u1ea3n ghi m\u1edbi \u0111\u1ea3m b\u1ea3o r\u1eb1ng c\u00e2y B+ v\u1eabn \u1edf tr\u1ea1ng th\u00e1i \u0111\u01b0\u1ee3c t\u1ed1i \u01b0u h\u00f3a. <\/span><span style=\"font-weight: 400;\">Ngo\u00e0i ra, kh\u00f4ng gi\u1ed1ng nh\u01b0 clustered-index, m\u1ed7i b\u1ea3ng c\u00f3 th\u1ec3 c\u00f3 nhi\u1ec1u non-clustered index.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Non-Clustered Index ph\u00f9 h\u1ee3p cho c\u00e1c c\u1ed9t kh\u00f4ng c\u1ea7n s\u1eafp x\u1ebfp d\u1eef li\u1ec7u v\u1eadt l\u00fd, nh\u01b0ng \u0111\u01b0\u1ee3c truy v\u1ea5n th\u01b0\u1eddng xuy\u00ean. V\u00ed d\u1ee5, trong m\u1ed9t b\u1ea3ng ng\u01b0\u1eddi d\u00f9ng, n\u1ebfu b\u1ea1n c\u1ea7n truy v\u1ea5n d\u1eef li\u1ec7u th\u01b0\u1eddng xuy\u00ean d\u1ef1a tr\u00ean \u0111\u1ecba ch\u1ec9 email, th\u00ec s\u1eed d\u1ee5ng Non-Clustered Index cho c\u1ed9t <\/span><span style=\"font-weight: 400;\">email<\/span><span style=\"font-weight: 400;\"> s\u1ebd gi\u00fap t\u0103ng t\u1ed1c \u0111\u1ed9 truy v\u1ea5n.<\/span><\/p>\n<h3><b>Unique index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">L\u00e0 lo\u1ea1i index \u0111\u1ea3m b\u1ea3o kh\u00f4ng c\u00f3 hai b\u1ea3n ghi n\u00e0o trong b\u1ea3ng c\u00f3 c\u00f9ng gi\u00e1 tr\u1ecb trong c\u00e1c c\u1ed9t \u0111\u01b0\u1ee3c l\u1eadp ch\u1ec9 m\u1ee5c.\u00a0 Unique Index th\u01b0\u1eddng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng trong c\u00e1c tr\u01b0\u1eddng h\u1ee3p c\u1ea7n \u0111\u1ea3m b\u1ea3o r\u1eb1ng kh\u00f4ng c\u00f3 hai b\u1ea3n ghi n\u00e0o c\u00f3 gi\u00e1 tr\u1ecb tr\u00f9ng l\u1eb7p \u1edf m\u1ed9t c\u1ed9t ho\u1eb7c nhi\u1ec1u c\u1ed9t, gi\u00fap b\u1ea3o to\u00e0n t\u00ednh to\u00e0n v\u1eb9n c\u1ee7a d\u1eef li\u1ec7u.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5, khi thi\u1ebft l\u1eadp m\u1ed9t h\u1ec7 th\u1ed1ng \u0111\u0103ng k\u00fd t\u00e0i kho\u1ea3n, b\u1ea1n c\u00f3 th\u1ec3 d\u00f9ng Unique Index tr\u00ean c\u1ed9t <\/span><span style=\"font-weight: 400;\">email<\/span><span style=\"font-weight: 400;\"> \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o r\u1eb1ng kh\u00f4ng c\u00f3 hai ng\u01b0\u1eddi d\u00f9ng n\u00e0o s\u1eed d\u1ee5ng c\u00f9ng m\u1ed9t email.<\/span><\/p>\n<h3><b>Full-text index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">\u0110\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 t\u1ed1i \u01b0u h\u00f3a c\u00e1c truy v\u1ea5n t\u00ecm ki\u1ebfm v\u0103n b\u1ea3n l\u1edbn, h\u1ed7 tr\u1ee3 c\u00e1c ki\u1ec3u t\u00ecm ki\u1ebfm ph\u1ee9c t\u1ea1p nh\u01b0 t\u00ecm ki\u1ebfm theo t\u1eeb kh\u00f3a, c\u1ee5m t\u1eeb ho\u1eb7c \u0111\u1ed9 t\u01b0\u01a1ng \u0111\u1ed3ng. Full-text index gi\u00fap t\u00ecm ki\u1ebfm t\u1eeb kh\u00f3a trong c\u00e1c v\u0103n b\u1ea3n d\u00e0i hi\u1ec7u qu\u1ea3 h\u01a1n so v\u1edbi vi\u1ec7c s\u1eed d\u1ee5ng c\u00e1c lo\u1ea1i index kh\u00e1c.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Full-text Index th\u01b0\u1eddng ph\u00f9 h\u1ee3p cho c\u00e1c b\u1ea3ng l\u01b0u tr\u1eef d\u1eef li\u1ec7u v\u0103n b\u1ea3n d\u00e0i, nh\u01b0 trong h\u1ec7 th\u1ed1ng qu\u1ea3n l\u00fd n\u1ed9i dung ho\u1eb7c blog. Khi ng\u01b0\u1eddi d\u00f9ng mu\u1ed1n t\u00ecm ki\u1ebfm c\u00e1c b\u00e0i vi\u1ebft ch\u1ee9a m\u1ed9t s\u1ed1 t\u1eeb kh\u00f3a nh\u1ea5t \u0111\u1ecbnh, Full-text Index s\u1ebd gi\u00fap t\u0103ng t\u1ed1c \u0111\u1ed9 t\u00ecm ki\u1ebfm c\u00e1c chu\u1ed7i v\u0103n b\u1ea3n d\u00e0i.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Tuy nhi\u00ean, Full-text Index kh\u00f4ng c\u00f3 s\u1eb5n \u1edf t\u1ea5t c\u1ea3 h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u, ch\u00fang th\u01b0\u1eddng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng trong MySQL hay SQL Server.<\/span><\/p>\n<h3><b>Composite index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">L\u00e0 lo\u1ea1i index \u0111\u01b0\u1ee3c t\u1ea1o tr\u00ean nhi\u1ec1u c\u1ed9t thay v\u00ec ch\u1ec9 m\u1ed9t c\u1ed9t \u0111\u01a1n l\u1ebb. N\u00f3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng khi truy v\u1ea5n th\u01b0\u1eddng t\u00ecm ki\u1ebfm tr\u00ean nhi\u1ec1u c\u1ed9t, gi\u00fap t\u0103ng hi\u1ec7u su\u1ea5t khi c\u1ea7n so s\u00e1nh nhi\u1ec1u tr\u01b0\u1eddng.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Composite Index th\u01b0\u1eddng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng trong c\u00e1c tr\u01b0\u1eddng h\u1ee3p khi truy v\u1ea5n c\u1ee7a b\u1ea1n d\u1ef1a tr\u00ean nhi\u1ec1u c\u1ed9t, m\u00e0 trong \u0111\u00f3, th\u1ee9 t\u1ef1 c\u00e1c c\u1ed9t c\u00f3 th\u1ec3 \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn hi\u1ec7u qu\u1ea3 truy v\u1ea5n. V\u00ed d\u1ee5, trong m\u1ed9t b\u1ea3ng <\/span><span style=\"font-weight: 400;\">orders<\/span><span style=\"font-weight: 400;\">, n\u1ebfu b\u1ea1n th\u01b0\u1eddng t\u00ecm ki\u1ebfm d\u1ef1a tr\u00ean c\u1ea3 <\/span><span style=\"font-weight: 400;\">customer_id<\/span><span style=\"font-weight: 400;\"> v\u00e0 <\/span><span style=\"font-weight: 400;\">order_date<\/span><span style=\"font-weight: 400;\">, th\u00ec Composite Index tr\u00ean hai c\u1ed9t n\u00e0y s\u1ebd gi\u00fap c\u1ea3i thi\u1ec7n hi\u1ec7u su\u1ea5t truy v\u1ea5n.<\/span><\/p>\n<h2><span class=\"ez-toc-section\" id=\"Phan_loai_index_trong_database_theo_cau_truc\"><\/span><b>Ph\u00e2n lo\u1ea1i index trong database theo c\u1ea5u tr\u00fac<\/b><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><span style=\"font-weight: 400;\">C\u00f3 nhi\u1ec1u lo\u1ea1i c\u1ea5u tr\u00fac d\u1eef li\u1ec7u kh\u00e1c nhau \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 x\u00e2y d\u1ef1ng ch\u1ec9 m\u1ee5c (indexes) trong c\u01a1 s\u1edf d\u1eef li\u1ec7u, m\u1ed9t s\u1ed1 lo\u1ea1i ph\u1ed5 bi\u1ebfn g\u1ed3m:<\/span><\/p>\n<h3><b>B+ tree index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">L\u00e0 m\u1ed9t trong nh\u1eefng c\u1ea5u tr\u00fac ch\u1ec9 m\u1ee5c ph\u1ed5 bi\u1ebfn nh\u1ea5t v\u1edbi \u0111\u1eb7c \u0111i\u1ec3m t\u1ef1 c\u00e2n b\u1eb1ng v\u1edbi c\u00e1c n\u00fat l\u00e1 ch\u1ee9a con tr\u1ecf \u0111\u1ebfn d\u1eef li\u1ec7u th\u1ef1c t\u1ebf. \u0110\u1eb7c \u0111i\u1ec3m c\u1ee7a n\u00f3 l\u00e0 m\u1ed7i n\u00fat c\u00f3 th\u1ec3 ch\u1ee9a nhi\u1ec1u kh\u00f3a v\u00e0 con tr\u1ecf \u0111\u1ebfn c\u00e1c n\u00fat con, gi\u00fap t\u1ed1i \u01b0u h\u00f3a cho c\u00e1c truy v\u1ea5n ph\u1ea1m vi (range queries). C\u1ea5u tr\u00fac n\u00e0y cho ph\u00e9p t\u00ecm ki\u1ebfm, th\u00eam v\u00e0 x\u00f3a d\u1eef li\u1ec7u m\u1ed9t c\u00e1ch hi\u1ec7u qu\u1ea3, ph\u00f9 h\u1ee3p v\u1edbi h\u1ea7u h\u1ebft c\u00e1c h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/span><\/p>\n<h3><b>Hash index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">L\u00e0 lo\u1ea1i ch\u1ec9 m\u1ee5c s\u1eed d\u1ee5ng h\u00e0m b\u0103m (hash function) \u0111\u1ec3 \u00e1nh x\u1ea1 c\u00e1c kh\u00f3a \u0111\u1ebfn v\u1ecb tr\u00ed l\u01b0u tr\u1eef c\u1ee5 th\u1ec3 trong ch\u1ec9 m\u1ee5c. Hash index ho\u1ea1t \u0111\u1ed9ng r\u1ea5t nhanh v\u1edbi c\u00e1c truy v\u1ea5n t\u00ecm ki\u1ebfm kh\u1edbp ch\u00ednh x\u00e1c (exact-match queries) <\/span><span style=\"font-weight: 400;\">(=)<\/span><span style=\"font-weight: 400;\">, nh\u01b0ng kh\u00f4ng ph\u00f9 h\u1ee3p cho c\u00e1c truy v\u1ea5n ph\u1ea1m vi <\/span><span style=\"font-weight: 400;\">(&gt;, &lt;, BETWEEN)<\/span><span style=\"font-weight: 400;\">. Ch\u1ec9 m\u1ee5c n\u00e0y th\u01b0\u1eddng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng trong c\u00e1c c\u01a1 s\u1edf d\u1eef li\u1ec7u d\u1ef1a tr\u00ean b\u1ed9 nh\u1edb ho\u1eb7c l\u00e0m ch\u1ec9 m\u1ee5c ph\u1ee5.<\/span><\/p>\n<h3><b>Bitmap index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Bitmap indexes th\u01b0\u1eddng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng cho c\u00e1c c\u1ed9t c\u00f3 \u0111\u1ed9 ph\u00e2n bi\u1ec7t th\u1ea5p (low-cardinality), ngh\u0129a l\u00e0 c\u00e1c c\u1ed9t ch\u1ec9 c\u00f3 m\u1ed9t s\u1ed1 l\u01b0\u1ee3ng nh\u1ecf gi\u00e1 tr\u1ecb duy nh\u1ea5t. Lo\u1ea1i ch\u1ec9 m\u1ee5c n\u00e0y r\u1ea5t hi\u1ec7u qu\u1ea3 trong c\u00e1c truy v\u1ea5n ph\u1ee9c t\u1ea1p v\u00e0 kh\u1ed1i l\u01b0\u1ee3ng c\u00f4ng vi\u1ec7c thi\u00ean v\u1ec1 \u0111\u1ecdc, nh\u01b0ng l\u1ea1i k\u00e9m hi\u1ec7u qu\u1ea3 cho c\u00e1c thao t\u00e1c ghi d\u1eef li\u1ec7u th\u01b0\u1eddng xuy\u00ean.<\/span><\/p>\n<h3><b>Sparse Index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Sparse Index l\u01b0u tr\u1eef th\u00f4ng tin ch\u1ec9 v\u1ec1 m\u1ed9t t\u1eadp h\u1ee3p con c\u1ee7a c\u00e1c d\u00f2ng d\u1eef li\u1ec7u trong b\u1ea3ng, thay v\u00ec l\u01b0u tr\u1eef to\u00e0n b\u1ed9 b\u1ea3ng. \u0110i\u1ec1u n\u00e0y gi\u00fap ti\u1ebft ki\u1ec7m kh\u00f4ng gian v\u00e0 t\u1ed1i \u01b0u h\u00f3a hi\u1ec7u su\u1ea5t truy v\u1ea5n trong c\u00e1c tr\u01b0\u1eddng h\u1ee3p kh\u00f4ng c\u1ea7n index to\u00e0n b\u1ed9 d\u1eef li\u1ec7u.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Ngo\u00e0i c\u00e1c lo\u1ea1i ch\u1ec9 m\u1ee5c tr\u00ean, c\u00f2n c\u00f3 nhi\u1ec1u lo\u1ea1i kh\u00e1c nh\u01b0 LSM Tree, GiST, Gin, R-Tree, SSTable,&#8230; ph\u1ee5c v\u1ee5 cho c\u00e1c tr\u01b0\u1eddng h\u1ee3p kh\u00e1c nhau.<\/span><\/p>\n<h2><span class=\"ez-toc-section\" id=\"Phan_loai_index_trong_database_theo_phuong_thuc_quan_ly\"><\/span><b>Ph\u00e2n lo\u1ea1i index trong database theo ph\u01b0\u01a1ng th\u1ee9c qu\u1ea3n l\u00fd<\/b><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><span style=\"font-weight: 400;\">Ph\u00e2n lo\u1ea1i n\u00e0y d\u1ef1a tr\u00ean c\u00e1ch m\u00e0 index \u0111\u01b0\u1ee3c qu\u1ea3n l\u00fd trong h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/span><\/p>\n<h3><b>Primary Index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">L\u00e0 ch\u1ec9 m\u1ee5c \u0111\u01b0\u1ee3c t\u1ea1o tr\u00ean c\u1ed9t kh\u00f3a ch\u00ednh (primary key) c\u1ee7a b\u1ea3ng. Primary index gi\u00fap \u0111\u1ea3m b\u1ea3o t\u00ednh duy nh\u1ea5t c\u1ee7a m\u1ed7i b\u1ea3n ghi trong b\u1ea3ng v\u00e0 t\u0103ng t\u1ed1c \u0111\u1ed9 t\u00ecm ki\u1ebfm theo c\u1ed9t kh\u00f3a ch\u00ednh.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Primary Index th\u01b0\u1eddng l\u00e0 clustered index, c\u00e1c b\u1ea3n ghi trong b\u1ea3ng \u0111\u01b0\u1ee3c s\u1eafp x\u1ebfp v\u1eadt l\u00fd d\u1ef1a tr\u00ean gi\u00e1 tr\u1ecb c\u1ee7a c\u00e1c c\u1ed9t kh\u00f3a ch\u00ednh. V\u00ed d\u1ee5 ta c\u00f3 m\u1ed9t b\u1ea3ng <\/span><span style=\"font-weight: 400;\">employees<\/span><span style=\"font-weight: 400;\">, Primary Index \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng tr\u00ean c\u1ed9t <\/span><span style=\"font-weight: 400;\">employee_id<\/span><span style=\"font-weight: 400;\"> gi\u00fap \u0111\u1ea3m b\u1ea3o r\u1eb1ng m\u1ed7i b\u1ea3n ghi l\u00e0 duy nh\u1ea5t v\u00e0 t\u0103ng t\u1ed1c \u0111\u1ed9 truy v\u1ea5n t\u00ecm ki\u1ebfm theo <\/span><span style=\"font-weight: 400;\">employee_id<\/span><span style=\"font-weight: 400;\">.<\/span><\/p>\n<h3><b>Secondary Index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">L\u00e0 ch\u1ec9 m\u1ee5c \u0111\u01b0\u1ee3c t\u1ea1o tr\u00ean c\u00e1c c\u1ed9t kh\u00f4ng ph\u1ea3i kh\u00f3a ch\u00ednh \u0111\u1ec3 t\u0103ng t\u1ed1c \u0111\u1ed9 t\u00ecm ki\u1ebfm tr\u00ean c\u00e1c c\u1ed9t kh\u00e1c ngo\u00e0i kh\u00f3a ch\u00ednh. Secondary index r\u1ea5t h\u1eefu \u00edch khi c\u1ea7n t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n tr\u00ean nhi\u1ec1u c\u1ed9t kh\u00f4ng ph\u1ea3i l\u00e0 kh\u00f3a ch\u00ednh.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Secondary Index hay \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng cho c\u00e1c c\u1ed9t kh\u00f4ng ph\u1ea3i l\u00e0 kh\u00f3a ch\u00ednh nh\u01b0ng th\u01b0\u1eddng \u0111\u01b0\u1ee3c truy v\u1ea5n. V\u00ed d\u1ee5, trong b\u1ea3ng <\/span><span style=\"font-weight: 400;\">customers<\/span><span style=\"font-weight: 400;\">, n\u1ebfu c\u00e1c truy v\u1ea5n th\u01b0\u1eddng \u0111\u01b0\u1ee3c th\u1ef1c hi\u1ec7n d\u1ef1a tr\u00ean <\/span><span style=\"font-weight: 400;\">phone_number<\/span><span style=\"font-weight: 400;\"> (m\u00e0 kh\u00f4ng ph\u1ea3i l\u00e0 kh\u00f3a ch\u00ednh), th\u00ec s\u1eed d\u1ee5ng Secondary Index tr\u00ean c\u1ed9t n\u00e0y s\u1ebd c\u1ea3i thi\u1ec7n hi\u1ec7u su\u1ea5t truy v\u1ea5n.<\/span><\/p>\n<h2><span class=\"ez-toc-section\" id=\"Mot_so_thao_tac_voi_index_trong_database\"><\/span><b>M\u1ed9t s\u1ed1 thao t\u00e1c v\u1edbi index trong database<\/b><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<h3><b>T\u1ea1o index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">\u0110\u1ec3 t\u1ea1o index trong database, b\u1ea1n c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng l\u1ec7nh <\/span><span style=\"font-weight: 400;\">CREATE INDEX<\/span><span style=\"font-weight: 400;\">. Vi\u1ec7c t\u1ea1o index s\u1ebd gi\u00fap c\u1ea3i thi\u1ec7n hi\u1ec7u su\u1ea5t truy v\u1ea5n, \u0111\u1eb7c bi\u1ec7t l\u00e0 khi b\u1ea3ng ch\u1ee9a nhi\u1ec1u d\u1eef li\u1ec7u v\u00e0 c\u1ea7n truy v\u1ea5n th\u01b0\u1eddng xuy\u00ean tr\u00ean c\u00e1c c\u1ed9t c\u1ee5 th\u1ec3.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">C\u00fa ph\u00e1p:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE INDEX index_name ON table_name (column1, column2, ...);<\/span><\/pre>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 \u0111\u1ec3 t\u1ea1o m\u1ed9t Non-Clustered Index tr\u00ean c\u1ed9t <\/span><i><span style=\"font-weight: 400;\">Name<\/span><\/i><span style=\"font-weight: 400;\"> c\u1ee7a b\u1ea3ng <\/span><i><span style=\"font-weight: 400;\">Students<\/span><\/i><span style=\"font-weight: 400;\"> \u0111\u1ec3 t\u0103ng t\u1ed1c \u0111\u1ed9 t\u00ecm ki\u1ebfm sinh vi\u00ean theo t\u00ean ta d\u00f9ng c\u00fa ph\u00e1p sau:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE INDEX idx_students_name ON Students (Name);<\/span><\/pre>\n<p><span style=\"font-weight: 400;\">\u0110\u00f4i khi, b\u1ea1n c\u1ea7n t\u1ea1o m\u1ed9t index tr\u00ean nhi\u1ec1u c\u1ed9t c\u00f9ng l\u00fac \u0111\u1ec3 t\u1ed1i \u01b0u cho c\u00e1c truy v\u1ea5n k\u1ebft h\u1ee3p nhi\u1ec1u \u0111i\u1ec1u ki\u1ec7n v\u00e0 index n\u00e0y g\u1ecdi l\u00e0 composite index.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 \u0111\u1ec3 t\u1ea1o m\u1ed9t Composite Index tr\u00ean c\u1ea3 hai c\u1ed9t <\/span><i><span style=\"font-weight: 400;\">Name<\/span><\/i><span style=\"font-weight: 400;\"> v\u00e0 <\/span><i><span style=\"font-weight: 400;\">Age<\/span><\/i><span style=\"font-weight: 400;\"> ta s\u1eed d\u1ee5ng c\u00fa ph\u00e1p sau:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE INDEX idx_students_name_age ON Students (Name, Age);<\/span><\/pre>\n<h3><b>T\u1ea1o unique index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">N\u1ebfu b\u1ea1n mu\u1ed1n \u0111\u1ea3m b\u1ea3o r\u1eb1ng c\u00e1c gi\u00e1 tr\u1ecb trong m\u1ed9t c\u1ed9t l\u00e0 duy nh\u1ea5t (nh\u01b0 s\u1ed1 \u0111\u1ecbnh danh ho\u1eb7c email), b\u1ea1n c\u00f3 th\u1ec3 d\u00f9ng Unique Index. Unique index \u0111\u1ea3m b\u1ea3o kh\u00f4ng c\u00f3 hai b\u1ea3n ghi n\u00e0o c\u00f3 c\u00f9ng gi\u00e1 tr\u1ecb trong c\u1ed9t \u0111\u01b0\u1ee3c index.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">C\u00fa ph\u00e1p:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE UNIQUE INDEX index_name ON table_name (column1, column2, ...);<\/span><\/pre>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 \u0111\u1ec3 t\u1ea1o Unique Index tr\u00ean c\u1ed9t <\/span><i><span style=\"font-weight: 400;\">Email<\/span><\/i><span style=\"font-weight: 400;\"> c\u1ee7a b\u1ea3ng <\/span><i><span style=\"font-weight: 400;\">Students<\/span><\/i><span style=\"font-weight: 400;\"> ta s\u1eed d\u1ee5ng c\u00fa ph\u00e1p sau:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE UNIQUE INDEX idx_students_email_unique ON Students (Email);<\/span><\/pre>\n<h3><b>X\u00f3a index<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Khi kh\u00f4ng c\u00f2n c\u1ea7n thi\u1ebft s\u1eed d\u1ee5ng index ho\u1eb7c n\u1ebfu index l\u00e0m gi\u1ea3m hi\u1ec7u su\u1ea5t ghi (<\/span><span style=\"font-weight: 400;\">INSERT<\/span><span style=\"font-weight: 400;\">, <\/span><span style=\"font-weight: 400;\">UPDATE<\/span><span style=\"font-weight: 400;\">, <\/span><span style=\"font-weight: 400;\">DELETE<\/span><span style=\"font-weight: 400;\">), b\u1ea1n c\u00f3 th\u1ec3 x\u00f3a index b\u1eb1ng c\u00e1ch s\u1eed d\u1ee5ng l\u1ec7nh <\/span><span style=\"font-weight: 400;\">DROP INDEX<\/span><span style=\"font-weight: 400;\">.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">C\u00fa ph\u00e1p:<\/span><\/p>\n<pre>DROP INDEX index_name ON table_name;<\/pre>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 \u0111\u1ec3 x\u00f3a Non-Clustered Index tr\u00ean c\u1ed9t <\/span><i><span style=\"font-weight: 400;\">Name<\/span><\/i><span style=\"font-weight: 400;\"> v\u00e0 t\u1eeb \u0111\u00f3 c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd kh\u00f4ng c\u00f2n s\u1eed d\u1ee5ng index n\u00e0y khi th\u1ef1c hi\u1ec7n truy v\u1ea5n n\u1eefa, ta d\u00f9ng c\u00fa ph\u00e1p sau:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">DROP INDEX idx_students_name;<\/span><\/pre>\n<h3><b>Ki\u1ec3m tra index hi\u1ec7n c\u00f3<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">\u0110\u1ec3 xem c\u00e1c index hi\u1ec7n c\u00f3 trong m\u1ed9t b\u1ea3ng, b\u1ea1n c\u00f3 th\u1ec3 truy v\u1ea5n h\u1ec7 th\u1ed1ng th\u00f4ng tin c\u1ee7a c\u01a1 s\u1edf d\u1eef li\u1ec7u. V\u00ed d\u1ee5, trong MySQL, b\u1ea1n c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng c\u00e2u l\u1ec7nh sau \u0111\u1ec3 ki\u1ec3m tra c\u00e1c index tr\u00ean b\u1ea3ng <\/span><i><span style=\"font-weight: 400;\">Students<\/span><\/i><span style=\"font-weight: 400;\">:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">SHOW INDEX FROM Students;<\/span><\/pre>\n<h3><b>Xem index \u0111\u01b0\u1ee3c \u00e1p d\u1ee5ng trong m\u1ed9t c\u00e2u truy v\u1ea5n<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">\u0110\u1ec3 ki\u1ec3m tra ch\u1ec9 m\u1ee5c n\u00e0o \u0111\u01b0\u1ee3c \u00e1p d\u1ee5ng trong m\u1ed9t c\u00e2u truy v\u1ea5n v\u00e0 xem c\u00e1ch c\u01a1 s\u1edf d\u1eef li\u1ec7u t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n, ta c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng <\/span><span style=\"font-weight: 400;\">EXPLAIN<\/span><span style=\"font-weight: 400;\">. C\u00e2u l\u1ec7nh n\u00e0y s\u1ebd hi\u1ec3n th\u1ecb th\u00f4ng tin v\u1ec1 k\u1ebf ho\u1ea1ch th\u1ef1c hi\u1ec7n truy v\u1ea5n, bao g\u1ed3m ch\u1ec9 m\u1ee5c \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng, s\u1ed1 l\u01b0\u1ee3ng b\u1ea3n ghi \u0111\u01b0\u1ee3c qu\u00e9t v\u00e0 nhi\u1ec1u th\u00f4ng tin kh\u00e1c.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">C\u00fa ph\u00e1p:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">EXPLAIN &lt;c\u00e2u truy v\u1ea5n&gt;<\/span><\/pre>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 \u0111\u1ec3 ki\u1ec3m tra xem li\u1ec7u ch\u1ec9 m\u1ee5c <\/span><span style=\"font-weight: 400;\">idx_students_name<\/span><span style=\"font-weight: 400;\"> c\u00f3 \u0111\u01b0\u1ee3c \u00e1p d\u1ee5ng khi t\u00ecm ki\u1ebfm sinh vi\u00ean theo t\u00ean trong b\u1ea3ng <\/span><span style=\"font-weight: 400;\">Students<\/span><span style=\"font-weight: 400;\"> hay kh\u00f4ng, b\u1ea1n c\u00f3 th\u1ec3 d\u00f9ng l\u1ec7nh sau:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">EXPLAIN SELECT * FROM Students WHERE Name = 'John';<\/span><\/pre>\n<h3><b>T\u1ea1o index v\u1edbi \u0111i\u1ec1u ki\u1ec7n l\u1ecdc (Filtered Index)<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Trong m\u1ed9t s\u1ed1 h\u1ec7 qu\u1ea3n tr\u1ecb nh\u01b0 SQL Server, khi b\u1ea1n ch\u1ec9 mu\u1ed1n t\u1ea1o ch\u1ec9 m\u1ee5c tr\u00ean nh\u1eefng b\u1ea3n ghi th\u1ecfa m\u00e3n m\u1ed9t \u0111i\u1ec1u ki\u1ec7n c\u1ee5 th\u1ec3, b\u1ea1n c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng <\/span><b>Filtered Index<\/b><span style=\"font-weight: 400;\">. Index n\u00e0y gi\u00fap gi\u1ea3m k\u00edch th\u01b0\u1edbc index v\u00e0 c\u1ea3i thi\u1ec7n hi\u1ec7u su\u1ea5t cho c\u00e1c truy v\u1ea5n ch\u1ec9 li\u00ean quan \u0111\u1ebfn t\u1eadp h\u1ee3p con c\u1ee7a d\u1eef li\u1ec7u.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 \u0111\u1ec3 t\u1ea1o ch\u1ec9 m\u1ee5c cho nh\u1eefng sinh vi\u00ean tr\u00ean 18 tu\u1ed5i trong b\u1ea3ng <\/span><span style=\"font-weight: 400;\">Students<\/span><span style=\"font-weight: 400;\">, ta c\u00f3 c\u00fa ph\u00e1p nh\u01b0 sau:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE INDEX idx_students_age_filtered ON Students (Age) WHERE Age &gt; 18;<\/span><\/pre>\n<h3><b>S\u1eed d\u1ee5ng index \u0111\u1ec3 s\u1eafp x\u1ebfp<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Index s\u1eafp x\u1ebfp l\u00e0 lo\u1ea1i ch\u1ec9 m\u1ee5c \u0111\u01b0\u1ee3c t\u1ea1o ra \u0111\u1ec3 t\u1ed1i \u01b0u h\u00f3a vi\u1ec7c s\u1eafp x\u1ebfp d\u1eef li\u1ec7u theo th\u1ee9 t\u1ef1 t\u0103ng d\u1ea7n ho\u1eb7c gi\u1ea3m d\u1ea7n. Khi b\u1ea1n th\u01b0\u1eddng xuy\u00ean th\u1ef1c hi\u1ec7n c\u00e1c truy v\u1ea5n y\u00eau c\u1ea7u s\u1eafp x\u1ebfp d\u1eef li\u1ec7u (s\u1eed d\u1ee5ng m\u1ec7nh \u0111\u1ec1 <\/span><span style=\"font-weight: 400;\">ORDER BY<\/span><span style=\"font-weight: 400;\">), vi\u1ec7c s\u1eed d\u1ee5ng index s\u1eafp x\u1ebfp s\u1ebd gi\u00fap t\u0103ng t\u1ed1c \u0111\u1ed9 truy v\u1ea5n \u0111\u00e1ng k\u1ec3.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Trong c\u00e1c phi\u00ean b\u1ea3n MySQL tr\u01b0\u1edbc 8.0, vi\u1ec7c qu\u00e9t m\u1ed9t ch\u1ec9 m\u1ee5c theo th\u1ee9 t\u1ef1 ng\u01b0\u1ee3c c\u00f3 th\u1ec3 t\u1ed1n r\u1ea5t nhi\u1ec1u t\u00e0i nguy\u00ean v\u00e0 l\u00e0m gi\u1ea3m hi\u1ec7u su\u1ea5t do MySQL c\u1ea7n th\u1ef1c hi\u1ec7n s\u1eafp x\u1ebfp l\u1ea1i d\u1eef li\u1ec7u theo c\u00e1ch th\u1ee7 c\u00f4ng. Tuy nhi\u00ean, k\u1ec3 t\u1eeb phi\u00ean b\u1ea3n MySQL 8.0, ng\u01b0\u1eddi d\u00f9ng c\u00f3 th\u1ec3 t\u1ea1o ch\u1ec9 m\u1ee5c gi\u1ea3m d\u1ea7n (descending indexes), gi\u00fap vi\u1ec7c qu\u00e9t ch\u1ec9 m\u1ee5c theo th\u1ee9 t\u1ef1 ng\u01b0\u1ee3c tr\u1edf n\u00ean hi\u1ec7u qu\u1ea3 h\u01a1n m\u00e0 kh\u00f4ng l\u00e0m gi\u1ea3m hi\u1ec7u su\u1ea5t truy v\u1ea5n.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Ta c\u00f3 th\u1ec3 t\u1ea1o index s\u1eafp x\u1ebfp trong qu\u00e1 tr\u00ecnh t\u1ea1o b\u1ea3ng v\u1edbi c\u00fa ph\u00e1p:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE TABLE table_name (\u00a0<\/span>\r\n\r\n<span style=\"font-weight: 400;\">column_name1 datatype,\u00a0<\/span>\r\n\r\n<span style=\"font-weight: 400;\">column_name2 datatype,\u00a0<\/span>\r\n\r\n<span style=\"font-weight: 400;\">INDEX index_name1 (column_name1 ASC, column_name2 DESC),\u00a0<\/span>\r\n\r\n<span style=\"font-weight: 400;\">INDEX index_name2 (column_name1 DESC, column_name2 ASC)\u00a0<\/span>\r\n\r\n<span style=\"font-weight: 400;\">);<\/span><\/pre>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 \u0111\u1ec3 t\u1ea1o b\u1ea3ng <\/span><span style=\"font-weight: 400;\">Students<\/span><span style=\"font-weight: 400;\"> v\u1edbi ch\u1ec9 m\u1ee5c gi\u1ea3m d\u1ea7n tr\u00ean c\u1ed9t <\/span><span style=\"font-weight: 400;\">Name<\/span><span style=\"font-weight: 400;\"> v\u00e0 k\u1ebft h\u1ee3p v\u1edbi c\u1ed9t <\/span><span style=\"font-weight: 400;\">Age<\/span><span style=\"font-weight: 400;\"> theo th\u1ee9 t\u1ef1 t\u0103ng d\u1ea7n, ta s\u1eed d\u1ee5ng c\u00fa ph\u00e1p sau:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE TABLE Students (<\/span>\r\n\r\n<span style=\"font-weight: 400;\">\u00a0ID INT,\u00a0<\/span>\r\n\r\n<span style=\"font-weight: 400;\">Name VARCHAR(100),\u00a0<\/span>\r\n\r\n<span style=\"font-weight: 400;\">Age INT,\u00a0<\/span>\r\n\r\n<span style=\"font-weight: 400;\">INDEX idx_name_age (Name DESC, Age ASC)\u00a0<\/span>\r\n\r\n<span style=\"font-weight: 400;\">);<\/span><\/pre>\n<p><span style=\"font-weight: 400;\">Ho\u1eb7c b\u1ea1n c\u00f3 th\u1ec3 t\u1ea1o index cho b\u1ea3ng \u0111\u00e3 t\u1ed3n t\u1ea1i v\u1edbi c\u00fa ph\u00e1p:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE INDEX index_name ON table_name (column_name1 ASC, column_name2 DESC);<\/span><\/pre>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 gi\u1ea3 s\u1eed b\u1ea3ng <\/span><span style=\"font-weight: 400;\">Students<\/span><span style=\"font-weight: 400;\"> \u0111\u00e3 t\u1ed3n t\u1ea1i, v\u00e0 b\u1ea1n mu\u1ed1n t\u1ea1o m\u1ed9t ch\u1ec9 m\u1ee5c gi\u1ea3m d\u1ea7n tr\u00ean c\u1ed9t <\/span><span style=\"font-weight: 400;\">Name<\/span><span style=\"font-weight: 400;\"> \u0111\u1ec3 t\u1ed1i \u01b0u h\u00f3a c\u00e1c truy v\u1ea5n s\u1eafp x\u1ebfp theo t\u00ean sinh vi\u00ean gi\u1ea3m d\u1ea7n, b\u1ea1n c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng c\u00fa ph\u00e1p sau:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">CREATE INDEX idx_students_name_desc ON Students (Name DESC);<\/span><\/pre>\n<p><span style=\"font-weight: 400;\">Sau khi \u0111\u00e3 t\u1ea1o index <\/span><span style=\"font-weight: 400;\">idx_students_name_desc<\/span><span style=\"font-weight: 400;\">, ta c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng c\u00e2u truy v\u1ea5n sau \u0111\u1ec3 g\u1ecdi index n\u00e0y v\u00e0 s\u1eafp x\u1ebfp k\u1ebft qu\u1ea3 theo th\u1ee9 t\u1ef1 gi\u1ea3m d\u1ea7n c\u1ee7a c\u1ed9t <\/span><span style=\"font-weight: 400;\">Name<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">SELECT * FROM Students ORDER BY Name DESC;<\/span><\/pre>\n<h2><span class=\"ez-toc-section\" id=\"Mot_so_quy_tac_chon_index_index_trong_database_phu_hop\"><\/span><b>M\u1ed9t s\u1ed1 quy t\u1eafc ch\u1ecdn index index trong database ph\u00f9 h\u1ee3p<\/b><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><b>Truy xu\u1ea5t d\u1ef1a tr\u00ean m\u1ed9t tr\u01b0\u1eddng duy nh\u1ea5t<\/b><\/p>\n<p><span style=\"font-weight: 400;\">Khi truy v\u1ea5n th\u01b0\u1eddng xuy\u00ean d\u1ef1a tr\u00ean m\u1ed9t tr\u01b0\u1eddng c\u1ee5 th\u1ec3, vi\u1ec7c t\u1ea1o index tr\u00ean c\u1ed9t \u0111\u00f3 s\u1ebd gi\u00fap t\u1ed1i \u01b0u h\u00f3a hi\u1ec7u su\u1ea5t truy v\u1ea5n v\u00ec c\u01a1 s\u1edf d\u1eef li\u1ec7u ch\u1ec9 c\u1ea7n tra c\u1ee9u d\u1ef1a tr\u00ean ch\u1ec9 m\u1ee5c c\u1ee7a m\u1ed9t c\u1ed9t. V\u00ed d\u1ee5, n\u1ebfu b\u1ea1n th\u01b0\u1eddng xuy\u00ean t\u00ecm ki\u1ebfm sinh vi\u00ean d\u1ef1a tr\u00ean <\/span><i><span style=\"font-weight: 400;\">ID<\/span><\/i><span style=\"font-weight: 400;\">, vi\u1ec7c t\u1ea1o index tr\u00ean c\u1ed9t <\/span><i><span style=\"font-weight: 400;\">ID<\/span><\/i><span style=\"font-weight: 400;\"> s\u1ebd t\u0103ng t\u1ed1c \u0111\u1ed9 truy v\u1ea5n.<\/span><\/p>\n<p><b>Truy xu\u1ea5t d\u1ef1a tr\u00ean nhi\u1ec1u tr\u01b0\u1eddng v\u1edbi to\u00e1n t\u1eed AND<\/b><\/p>\n<p><span style=\"font-weight: 400;\">N\u1ebfu truy v\u1ea5n c\u1ee7a b\u1ea1n d\u1ef1a tr\u00ean nhi\u1ec1u c\u1ed9t v\u00e0 s\u1eed d\u1ee5ng to\u00e1n t\u1eed <\/span><span style=\"font-weight: 400;\">AND<\/span><span style=\"font-weight: 400;\">, b\u1ea1n c\u00f3 th\u1ec3 t\u1ea1o m\u1ed9t index k\u1ebft h\u1ee3p (concatenated index) tr\u00ean c\u00e1c c\u1ed9t n\u00e0y \u0111\u1ec3 c\u1ea3i thi\u1ec7n hi\u1ec7u su\u1ea5t. C\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd s\u1eed d\u1ee5ng index \u0111\u1ec3 t\u00ecm d\u1eef li\u1ec7u ph\u00f9 h\u1ee3p v\u1edbi c\u1ea3 hai \u0111i\u1ec1u ki\u1ec7n.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">V\u00ed d\u1ee5 \u0111\u1ec3 l\u1ea5y th\u00f4ng tin c\u1ee7a c\u00e1c sinh vi\u00ean c\u00f3 \u0111\u1ed9 tu\u1ed5i 20 v\u00e0 \u0111\u1ebfn t\u1eeb H\u00e0 N\u1ed9i th\u00ec vi\u1ec7c t\u1ea1o m\u1ed9t index k\u1ebft h\u1ee3p tr\u00ean c\u1ea3 c\u1ed9t <\/span><i><span style=\"font-weight: 400;\">Age<\/span><\/i><span style=\"font-weight: 400;\"> v\u00e0 <\/span><i><span style=\"font-weight: 400;\">City<\/span><\/i><span style=\"font-weight: 400;\"> s\u1ebd gi\u00fap vi\u1ec7c t\u00ecm th\u00f4ng tin nhanh ch\u00f3ng h\u01a1n.<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">SELECT * FROM Students WHERE Age = 20 AND City = 'Hanoi';<\/span><\/pre>\n<blockquote><p><b>L\u01b0u \u00fd<\/b><span style=\"font-weight: 400;\"> l\u00e0 th\u1ee9 t\u1ef1 c\u00e1c c\u1ed9t trong ch\u1ec9 m\u1ee5c k\u1ebft h\u1ee3p r\u1ea5t quan tr\u1ecdng. N\u1ebfu th\u1ee9 t\u1ef1 c\u00e1c c\u1ed9t trong ch\u1ec9 m\u1ee5c kh\u00f4ng kh\u1edbp v\u1edbi c\u00e1ch ch\u00fang \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng trong c\u00e2u truy v\u1ea5n, ch\u1ec9 m\u1ee5c c\u00f3 th\u1ec3 kh\u00f4ng \u0111\u01b0\u1ee3c t\u1eadn d\u1ee5ng hi\u1ec7u qu\u1ea3 ho\u1eb7c th\u1eadm ch\u00ed kh\u00f4ng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng. V\u00ed d\u1ee5, trong ch\u1ec9 m\u1ee5c k\u1ebft h\u1ee3p <\/span><span style=\"font-weight: 400;\">(Age, City)<\/span><span style=\"font-weight: 400;\">, ch\u1ec9 m\u1ee5c s\u1ebd ho\u1ea1t \u0111\u1ed9ng t\u1ed1t khi truy v\u1ea5n s\u1eed d\u1ee5ng c\u1ea3 hai c\u1ed9t ho\u1eb7c b\u1eaft \u0111\u1ea7u v\u1edbi c\u1ed9t \u0111\u1ea7u ti\u00ean <\/span><span style=\"font-weight: 400;\">Age<\/span><span style=\"font-weight: 400;\">.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">Tuy nhi\u00ean, n\u1ebfu b\u1ea1n ch\u1ec9 truy v\u1ea5n theo <\/span><span style=\"font-weight: 400;\">City<\/span><span style=\"font-weight: 400;\"> m\u00e0 kh\u00f4ng c\u00f3 <\/span><span style=\"font-weight: 400;\">Age<\/span><span style=\"font-weight: 400;\">, ch\u1ec9 m\u1ee5c n\u00e0y c\u00f3 th\u1ec3 s\u1ebd kh\u00f4ng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng hi\u1ec7u qu\u1ea3.<\/span><\/p><\/blockquote>\n<p><b>Truy xu\u1ea5t v\u1edbi to\u00e1n t\u1eed OR<\/b><\/p>\n<p><span style=\"font-weight: 400;\">Khi s\u1eed d\u1ee5ng to\u00e1n t\u1eed <\/span><span style=\"font-weight: 400;\">OR<\/span><span style=\"font-weight: 400;\">, vi\u1ec7c t\u1ea1o index th\u01b0\u1eddng <\/span><b>KH\u00d4NG<\/b><span style=\"font-weight: 400;\"> mang l\u1ea1i hi\u1ec7u su\u1ea5t cao v\u00ec c\u01a1 s\u1edf d\u1eef li\u1ec7u ph\u1ea3i ki\u1ec3m tra nhi\u1ec1u \u0111i\u1ec1u ki\u1ec7n \u0111\u1ed9c l\u1eadp. Trong tr\u01b0\u1eddng h\u1ee3p n\u00e0y, vi\u1ec7c t\u1ea1o index kh\u00f4ng mang l\u1ea1i nhi\u1ec1u l\u1ee3i \u00edch.<\/span><\/p>\n<p><b>Truy xu\u1ea5t k\u1ebft h\u1ee3p AND v\u00e0 OR<\/b><\/p>\n<p><span style=\"font-weight: 400;\">Khi \u0111i\u1ec1u ki\u1ec7n truy v\u1ea5n ch\u1ee9a c\u1ea3 <\/span><span style=\"font-weight: 400;\">AND<\/span><span style=\"font-weight: 400;\"> v\u00e0 <\/span><span style=\"font-weight: 400;\">OR<\/span><span style=\"font-weight: 400;\">, b\u1ea1n c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng index n\u1ebfu c\u00e1c \u0111i\u1ec1u ki\u1ec7n <\/span><span style=\"font-weight: 400;\">OR<\/span><span style=\"font-weight: 400;\"> \u0111\u01b0\u1ee3c nh\u00f3m l\u1ea1i. C\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd s\u1eed d\u1ee5ng index cho \u0111i\u1ec1u ki\u1ec7n <\/span><span style=\"font-weight: 400;\">AND<\/span><span style=\"font-weight: 400;\"> \u0111\u1ec3 truy xu\u1ea5t d\u1eef li\u1ec7u hi\u1ec7u qu\u1ea3 h\u01a1n.<\/span><\/p>\n<p><b>T\u1ea1o qu\u00e1 nhi\u1ec1u ch\u1ec9 m\u1ee5c tr\u00ean m\u1ed9t b\u1ea3ng<\/b><\/p>\n<p><span style=\"font-weight: 400;\">T\u1ea1o qu\u00e1 nhi\u1ec1u ch\u1ec9 m\u1ee5c tr\u00ean m\u1ed9t b\u1ea3ng c\u00f3 th\u1ec3 l\u00e0m t\u0103ng th\u1eddi gian th\u1ef1c hi\u1ec7n c\u00e1c thao t\u00e1c ghi (INSERT, UPDATE, DELETE), v\u00ec m\u1ed7i l\u1ea7n d\u1eef li\u1ec7u thay \u0111\u1ed5i, index c\u0169ng ph\u1ea3i \u0111\u01b0\u1ee3c c\u1eadp nh\u1eadt. \u0110i\u1ec1u n\u00e0y c\u00f3 th\u1ec3 l\u00e0m gi\u1ea3m hi\u1ec7u su\u1ea5t c\u1ee7a h\u1ec7 th\u1ed1ng khi th\u1ef1c hi\u1ec7n c\u00e1c thao t\u00e1c ghi.<\/span><\/p>\n<h3><b>\u0110\u1eb7t ch\u1ec9 m\u1ee5c tr\u00ean c\u00e1c c\u1ed9t c\u00f3 \u00edt gi\u00e1 tr\u1ecb ri\u00eang l\u1ebb<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">N\u1ebfu b\u1ea1n t\u1ea1o ch\u1ec9 m\u1ee5c tr\u00ean c\u00e1c c\u1ed9t c\u00f3 \u00edt gi\u00e1 tr\u1ecb ri\u00eang l\u1ebb (nh\u01b0 c\u1ed9t Gi\u1edbi t\u00ednh ch\u1ec9 c\u00f3 gi\u00e1 tr\u1ecb &#8220;Nam&#8221; ho\u1eb7c &#8220;N\u1eef&#8221;), th\u00ec ch\u1ec9 m\u1ee5c n\u00e0y s\u1ebd kh\u00f4ng mang l\u1ea1i l\u1ee3i \u00edch \u0111\u00e1ng k\u1ec3. \u0110i\u1ec1u n\u00e0y l\u00e0 do c\u01a1 s\u1edf d\u1eef li\u1ec7u ph\u1ea3i duy\u1ec7t qua nhi\u1ec1u b\u1ea3n ghi c\u00f3 c\u00f9ng gi\u00e1 tr\u1ecb, kh\u00f4ng ch\u1ec9 l\u00e0m gi\u1ea3m l\u1ee3i \u00edch c\u1ee7a ch\u1ec9 m\u1ee5c m\u00e0 c\u00f2n ti\u00eau t\u1ed1n t\u00e0i nguy\u00ean \u0111\u1ec3 duy tr\u00ec ch\u1ec9 m\u1ee5c \u0111\u00f3.<\/span><\/p>\n<h3><b>L\u1eadp ch\u1ec9 m\u1ee5c tr\u00ean c\u00e1c c\u1ed9t kh\u00f4ng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng trong truy v\u1ea5n<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">N\u1ebfu c\u1ed9t kh\u00f4ng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng th\u01b0\u1eddng xuy\u00ean trong c\u00e1c truy v\u1ea5n, vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c tr\u00ean c\u1ed9t \u0111\u00f3 l\u00e0 kh\u00f4ng c\u1ea7n thi\u1ebft v\u00e0 c\u00f3 th\u1ec3 l\u00e0m t\u0103ng t\u00e0i nguy\u00ean qu\u1ea3n l\u00fd m\u00e0 kh\u00f4ng c\u1ea3i thi\u1ec7n hi\u1ec7u su\u1ea5t truy v\u1ea5n. H\u00e3y ch\u1ec9 t\u1ea1o index tr\u00ean c\u00e1c c\u1ed9t m\u00e0 b\u1ea1n th\u1ef1c s\u1ef1 th\u01b0\u1eddng xuy\u00ean s\u1eed d\u1ee5ng trong c\u00e1c c\u00e2u truy v\u1ea5n.<\/span><\/p>\n<h3><b>L\u1eadp ch\u1ec9 m\u1ee5c tr\u00ean c\u00e1c c\u1ed9t th\u01b0\u1eddng xuy\u00ean b\u1ecb thay \u0111\u1ed5i<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">\u0110\u1eb7t ch\u1ec9 m\u1ee5c tr\u00ean c\u00e1c c\u1ed9t m\u00e0 gi\u00e1 tr\u1ecb th\u01b0\u1eddng xuy\u00ean thay \u0111\u1ed5i (nh\u01b0 c\u1ed9t <\/span><span style=\"font-weight: 400;\">updated_at<\/span><span style=\"font-weight: 400;\"> hay c\u1ed9t v\u1ec1 tr\u1ea1ng th\u00e1i,&#8230;) c\u00f3 th\u1ec3 l\u00e0m gi\u1ea3m hi\u1ec7u su\u1ea5t c\u1ee7a h\u1ec7 th\u1ed1ng. M\u1ed7i l\u1ea7n gi\u00e1 tr\u1ecb c\u1ee7a c\u1ed9t thay \u0111\u1ed5i, c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd ph\u1ea3i c\u1eadp nh\u1eadt ch\u1ec9 m\u1ee5c, l\u00e0m t\u0103ng chi ph\u00ed c\u1eadp nh\u1eadt v\u00e0 gi\u1ea3m hi\u1ec7u su\u1ea5t.<\/span><\/p>\n<h3><b>S\u1eed d\u1ee5ng ph\u00e9p t\u00ednh to\u00e1n tr\u00ean c\u1ed9t c\u00f3 ch\u1ec9 m\u1ee5c<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Khi s\u1eed d\u1ee5ng ph\u00e9p t\u00ednh to\u00e1n tr\u00ean c\u1ed9t c\u00f3 ch\u1ec9 m\u1ee5c trong truy v\u1ea5n, c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd <\/span><b>kh\u00f4ng th\u1ec3<\/b><span style=\"font-weight: 400;\"> s\u1eed d\u1ee5ng ch\u1ec9 m\u1ee5c, d\u1eabn \u0111\u1ebfn kh\u00f4ng c\u1ea3i thi\u1ec7n hi\u1ec7u su\u1ea5t truy v\u1ea5n. V\u00ed d\u1ee5, n\u1ebfu b\u1ea1n c\u00f3 ch\u1ec9 m\u1ee5c tr\u00ean c\u1ed9t <\/span><span style=\"font-weight: 400;\">Name<\/span><span style=\"font-weight: 400;\">, nh\u01b0ng truy v\u1ea5n nh\u01b0 sau:<\/span><\/p>\n<pre><span style=\"font-weight: 400;\">SELECT * FROM Students WHERE Name LIKE '%nguyen%';<\/span><\/pre>\n<p><span style=\"font-weight: 400;\">Trong tr\u01b0\u1eddng h\u1ee3p n\u00e0y, ch\u1ec9 m\u1ee5c kh\u00f4ng th\u1ec3 h\u1ed7 tr\u1ee3 qu\u00e1 tr\u00ecnh t\u00ecm ki\u1ebfm n\u00e0y v\u00ec vi\u1ec7c t\u00ecm ki\u1ebfm kh\u00f4ng kh\u1edbp ch\u00ednh x\u00e1c \u1edf \u0111\u1ea7u chu\u1ed7i. Ch\u1ec9 m\u1ee5c th\u01b0\u1eddng ch\u1ec9 ho\u1ea1t \u0111\u1ed9ng hi\u1ec7u qu\u1ea3 khi b\u1ea1n t\u00ecm ki\u1ebfm t\u1eeb \u0111\u1ea7u chu\u1ed7i. V\u00e0 \u0111i\u1ec1u n\u00e0y khi\u1ebfn truy v\u1ea5n m\u1ea5t nhi\u1ec1u th\u1eddi gian h\u01a1n v\u00ec c\u01a1 s\u1edf d\u1eef li\u1ec7u ph\u1ea3i qu\u00e9t to\u00e0n b\u1ed9 b\u1ea3ng thay v\u00ec s\u1eed d\u1ee5ng ch\u1ec9 m\u1ee5c \u0111\u1ec3 t\u00ecm ki\u1ebfm nhanh h\u01a1n.<\/span><\/p>\n<h2><span class=\"ez-toc-section\" id=\"Uu_diem_cua_index_trong_database\"><\/span><b>\u01afu \u0111i\u1ec3m c\u1ee7a index trong database<\/b><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>C\u1ea3i thi\u1ec7n hi\u1ec7u su\u1ea5t truy v\u1ea5n<\/b><span style=\"font-weight: 400;\">: Index gi\u00fap t\u0103ng t\u1ed1c \u0111\u1ed9 truy xu\u1ea5t d\u1eef li\u1ec7u t\u1eeb c\u01a1 s\u1edf d\u1eef li\u1ec7u. B\u1eb1ng c\u00e1ch t\u1ea1o ch\u1ec9 m\u1ee5c tr\u00ean m\u1ed9t c\u1ed9t, c\u01a1 s\u1edf d\u1eef li\u1ec7u c\u00f3 th\u1ec3 nhanh ch\u00f3ng t\u00ecm ki\u1ebfm c\u00e1c h\u00e0ng c\u00f3 gi\u00e1 tr\u1ecb c\u1ee5 th\u1ec3 m\u00e0 kh\u00f4ng c\u1ea7n qu\u00e9t to\u00e0n b\u1ed9 b\u1ea3ng.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>T\u1ed1i \u01b0u h\u00f3a s\u1eafp x\u1ebfp d\u1eef li\u1ec7u<\/b><span style=\"font-weight: 400;\">: Index gi\u00fap gi\u1ea3m b\u1edbt th\u1eddi gian s\u1eafp x\u1ebfp d\u1eef li\u1ec7u b\u1eb1ng c\u00e1ch ch\u1ec9 s\u1eafp x\u1ebfp c\u00e1c h\u00e0ng li\u00ean quan, thay v\u00ec to\u00e0n b\u1ed9 b\u1ea3ng.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Hi\u1ec7u su\u1ea5t \u1ed5n \u0111\u1ecbnh<\/b><span style=\"font-weight: 400;\">: Index gi\u00fap duy tr\u00ec hi\u1ec7u su\u1ea5t nh\u1ea5t qu\u00e1n khi k\u00edch th\u01b0\u1edbc b\u1ea3ng t\u0103ng l\u00ean. C\u00e1c truy v\u1ea5n s\u1ebd kh\u00f4ng b\u1ecb gi\u1ea3m t\u1ed1c \u0111\u1ed9 ngay c\u1ea3 khi s\u1ed1 l\u01b0\u1ee3ng h\u00e0ng t\u0103ng.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>\u0110\u1ea3m b\u1ea3o t\u00ednh to\u00e0n v\u1eb9n c\u1ee7a d\u1eef li\u1ec7u<\/b><span style=\"font-weight: 400;\">: Index c\u00f3 th\u1ec3 \u0111\u1ea3m b\u1ea3o r\u1eb1ng c\u00e1c gi\u00e1 tr\u1ecb \u0111\u01b0\u1ee3c nh\u1eadp v\u00e0o c\u00e1c c\u1ed9t l\u00e0 duy nh\u1ea5t (v\u00ed d\u1ee5: Unique Index), ng\u0103n ch\u1eb7n vi\u1ec7c l\u01b0u tr\u1eef d\u1eef li\u1ec7u tr\u00f9ng l\u1eb7p.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Gi\u1ea3m thi\u1ec3u vi\u1ec7c s\u1eed d\u1ee5ng t\u00e0i nguy\u00ean<\/b><span style=\"font-weight: 400;\">: Nh\u1edd vi\u1ec7c t\u0103ng t\u1ed1c \u0111\u1ed9 truy v\u1ea5n, c\u00e1c truy v\u1ea5n s\u1ebd ho\u00e0n th\u00e0nh nhanh h\u01a1n, \u0111\u1ed3ng ngh\u0129a v\u1edbi vi\u1ec7c gi\u1ea3m t\u1ea3i cho h\u1ec7 th\u1ed1ng. Khi th\u1eddi gian truy v\u1ea5n gi\u1ea3m, h\u1ec7 th\u1ed1ng s\u1ebd \u00edt ph\u1ea3i s\u1eed d\u1ee5ng CPU, b\u1ed9 nh\u1edb v\u00e0 c\u00e1c t\u00e0i nguy\u00ean kh\u00e1c, gi\u00fap c\u1ea3i thi\u1ec7n hi\u1ec7u su\u1ea5t t\u1ed5ng th\u1ec3 c\u1ee7a c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/span><\/li>\n<\/ul>\n<h2><span class=\"ez-toc-section\" id=\"Nhuoc_diem_cua_index_trong_database\"><\/span><b>Nh\u01b0\u1ee3c \u0111i\u1ec3m c\u1ee7a index trong database<\/b><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>T\u1ed1n th\u00eam kh\u00f4ng gian l\u01b0u tr\u1eef<\/b><span style=\"font-weight: 400;\">: Index y\u00eau c\u1ea7u th\u00eam kh\u00f4ng gian \u0111\u1ec3 l\u01b0u tr\u1eef c\u1ea5u tr\u00fac d\u1eef li\u1ec7u index, l\u00e0m t\u0103ng t\u1ed5ng k\u00edch th\u01b0\u1edbc c\u1ee7a c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>T\u0103ng chi ph\u00ed b\u1ea3o tr\u00ec c\u01a1 s\u1edf d\u1eef li\u1ec7u<\/b><span style=\"font-weight: 400;\">: M\u1ed7i khi d\u1eef li\u1ec7u trong b\u1ea3ng \u0111\u01b0\u1ee3c th\u00eam, x\u00f3a ho\u1eb7c c\u1eadp nh\u1eadt, index c\u0169ng c\u1ea7n \u0111\u01b0\u1ee3c c\u1eadp nh\u1eadt, \u0111i\u1ec1u n\u00e0y l\u00e0m t\u0103ng chi ph\u00ed b\u1ea3o tr\u00ec.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Gi\u1ea3m hi\u1ec7u su\u1ea5t ch\u00e8n v\u00e0 c\u1eadp nh\u1eadt<\/b><span style=\"font-weight: 400;\">: Vi\u1ec7c th\u00eam m\u1edbi ho\u1eb7c c\u1eadp nh\u1eadt d\u1eef li\u1ec7u c\u00f3 th\u1ec3 ch\u1eadm h\u01a1n v\u00ec c\u01a1 s\u1edf d\u1eef li\u1ec7u ph\u1ea3i c\u1eadp nh\u1eadt c\u1ea5u tr\u00fac index.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Kh\u00f3 l\u1ef1a ch\u1ecdn index ph\u00f9 h\u1ee3p<\/b><span style=\"font-weight: 400;\">: Quy\u1ebft \u0111\u1ecbnh ch\u1ecdn index n\u00e0o l\u00e0 t\u1ed1i \u01b0u c\u00f3 th\u1ec3 kh\u00f3 kh\u0103n v\u00e0 y\u00eau c\u1ea7u ph\u00e2n t\u00edch chi ti\u1ebft v\u1ec1 d\u1eef li\u1ec7u v\u00e0 c\u00e1c m\u1eabu truy v\u1ea5n.<\/span><\/li>\n<\/ul>\n<h2><span class=\"ez-toc-section\" id=\"Tong_ket_index_trong_database\"><\/span><b>T\u1ed5ng k\u1ebft index trong database<\/b><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><span style=\"font-weight: 400;\">Index trong c\u01a1 s\u1edf d\u1eef li\u1ec7u l\u00e0 m\u1ed9t c\u00f4ng c\u1ee5 quan tr\u1ecdng gi\u00fap t\u1ed1i \u01b0u h\u00f3a hi\u1ec7u su\u1ea5t truy v\u1ea5n, c\u1ea3i thi\u1ec7n t\u1ed1c \u0111\u1ed9 truy xu\u1ea5t d\u1eef li\u1ec7u v\u00e0 \u0111\u1ea3m b\u1ea3o t\u00ednh nh\u1ea5t qu\u00e1n c\u1ee7a h\u1ec7 th\u1ed1ng ngay c\u1ea3 khi d\u1eef li\u1ec7u t\u0103ng l\u00ean. Tuy nhi\u00ean, vi\u1ec7c s\u1eed d\u1ee5ng index c\u0169ng \u0111i k\u00e8m v\u1edbi nh\u1eefng th\u00e1ch th\u1ee9c nh\u01b0 t\u0103ng kh\u00f4ng gian l\u01b0u tr\u1eef v\u00e0 chi ph\u00ed b\u1ea3o tr\u00ec.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">\u0110\u1ec3 t\u1ed1i \u01b0u h\u00f3a c\u01a1 s\u1edf d\u1eef li\u1ec7u, c\u1ea7n hi\u1ec3u r\u00f5 c\u00e1c lo\u1ea1i index, c\u00e1ch s\u1eed d\u1ee5ng ch\u00fang v\u00e0 \u00e1p d\u1ee5ng c\u00e1c chi\u1ebfn l\u01b0\u1ee3c ph\u00f9 h\u1ee3p cho t\u1eebng lo\u1ea1i d\u1eef li\u1ec7u v\u00e0 y\u00eau c\u1ea7u truy v\u1ea5n. Khi \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u00fang c\u00e1ch, index c\u00f3 th\u1ec3 mang l\u1ea1i l\u1ee3i \u00edch l\u1edbn trong vi\u1ec7c \u0111\u1ea3m b\u1ea3o h\u1ec7 th\u1ed1ng c\u01a1 s\u1edf d\u1eef li\u1ec7u ho\u1ea1t \u0111\u1ed9ng hi\u1ec7u qu\u1ea3 v\u00e0 b\u1ec1n v\u1eefng.<\/span><\/p>\n<blockquote><p><em>\u0110\u1ecdc th\u00eam: <a href=\"https:\/\/itviec.com\/blog\/transaction-trong-database-la-gi\/\" target=\"_blank\" rel=\"noopener\"><strong>Transaction trong database: C\u00e1c thao t\u00e1c c\u01a1 b\u1ea3n v\u1edbi transaction<\/strong><\/a><\/em><\/p><\/blockquote>\n","protected":false},"excerpt":{"rendered":"<p>Hi\u1ec7u su\u1ea5t l\u00e0 m\u1ed9t y\u1ebfu t\u1ed1 c\u1ed1t l\u00f5i trong vi\u1ec7c x\u00e2y d\u1ef1ng c\u00e1c \u1ee9ng d\u1ee5ng ch\u1ea5t l\u01b0\u1ee3ng cao. M\u1ed9t trong nh\u1eefng kh\u00eda c\u1ea1nh quan tr\u1ecdng c\u1ee7a hi\u1ec7u su\u1ea5t ch\u00ednh l\u00e0 t\u1ed1c \u0111\u1ed9 truy xu\u1ea5t d\u1eef li\u1ec7u m\u00e0 \u1ee9ng d\u1ee5ng c\u1ea7n \u0111\u1ec3 ho\u1ea1t \u0111\u1ed9ng hi\u1ec7u qu\u1ea3. B\u00ean c\u1ea1nh vi\u1ec7c t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n v\u00e0 b\u1ed9 [&hellip;]<\/p>\n","protected":false},"author":209,"featured_media":81136,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_gspb_post_css":"","footnotes":""},"categories":[109],"tags":[],"class_list":["post-80847","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-chuyen-mon-it"],"blocksy_meta":[],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v26.8 (Yoast SEO v27.9) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>Index trong database: H\u01b0\u1edbng d\u1eabn c\u00e1ch s\u1eed d\u1ee5ng chi ti\u1ebft - ITviec Blog<\/title>\n<meta name=\"description\" content=\"Kh\u00e1m ph\u00e1 vai tr\u00f2 c\u1ee7a Index trong database, c\u00e1ch ho\u1ea1t \u0111\u1ed9ng, \u01b0u nh\u01b0\u1ee3c \u0111i\u1ec3m v\u00e0 c\u00e1ch ch\u1ecdn index ph\u00f9 h\u1ee3p \u0111\u1ec3 t\u1ed1i \u01b0u hi\u1ec7u su\u1ea5t truy v\u1ea5n d\u1eef li\u1ec7u.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/itviec.com\/blog\/index-trong-database\/\" \/>\n<meta property=\"og:locale\" content=\"vi_VN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Index trong database: H\u01b0\u1edbng d\u1eabn c\u00e1ch s\u1eed d\u1ee5ng chi ti\u1ebft\" \/>\n<meta property=\"og:description\" content=\"Hi\u1ec7u su\u1ea5t l\u00e0 m\u1ed9t y\u1ebfu t\u1ed1 c\u1ed1t l\u00f5i trong vi\u1ec7c x\u00e2y d\u1ef1ng c\u00e1c \u1ee9ng d\u1ee5ng ch\u1ea5t l\u01b0\u1ee3ng cao. 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