{"id":1667,"date":"2026-03-27T07:12:07","date_gmt":"2026-03-27T07:12:07","guid":{"rendered":"https:\/\/www.go-diagram.com\/vi\/self-referencing-entities-recursive-relationships-erd\/"},"modified":"2026-03-27T07:12:07","modified_gmt":"2026-03-27T07:12:07","slug":"self-referencing-entities-recursive-relationships-erd","status":"publish","type":"post","link":"https:\/\/www.go-diagram.com\/vn\/self-referencing-entities-recursive-relationships-erd\/","title":{"rendered":"H\u01b0\u1edbng d\u1eabn ERD: C\u00e1c th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n: Hi\u1ec3u v\u1ec1 c\u00e1c m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy trong ERD"},"content":{"rendered":"<p>Trong ki\u1ebfn tr\u00fac ph\u1ee9c t\u1ea1p c\u1ee7a thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u, \u00edt kh\u00e1i ni\u1ec7m n\u00e0o th\u00e1ch th\u1ee9c c\u00e1c k\u1ef9 s\u01b0 b\u1eb1ng th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n. C\u00f2n \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy, m\u1eabu n\u00e0y cho ph\u00e9p m\u1ed9t b\u1ea3ng li\u00ean k\u1ebft v\u1edbi ch\u00ednh n\u00f3, gi\u00fap m\u00f4 h\u00ecnh h\u00f3a c\u00e1c c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p v\u00e0 ph\u1ee9c t\u1ea1p trong m\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 ph\u1eb3ng. Hi\u1ec3u c\u00e1ch tri\u1ec3n khai \u0111\u00fang s\u1ebd l\u00e0 y\u1ebfu t\u1ed1 then ch\u1ed1t \u0111\u1ec3 duy tr\u00ec t\u00ednh to\u00e0n v\u1eb9n d\u1eef li\u1ec7u v\u00e0 hi\u1ec7u su\u1ea5t truy v\u1ea5n.<\/p>\n<p>Khi thi\u1ebft k\u1ebf s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 (ERD), h\u1ea7u h\u1ebft c\u00e1c m\u1ed1i quan h\u1ec7 k\u1ebft n\u1ed1i hai th\u1ef1c th\u1ec3 kh\u00e1c nhau. Tuy nhi\u00ean, d\u1eef li\u1ec7u th\u1ef1c t\u1ebf th\u01b0\u1eddng \u0111\u00f2i h\u1ecfi m\u1ed9t th\u1ef1c th\u1ec3 duy nh\u1ea5t ph\u1ea3i li\u00ean k\u1ebft tr\u1edf l\u1ea1i v\u1edbi ch\u00ednh lo\u1ea1i th\u1ef1c th\u1ec3 \u0111\u00f3. M\u1ed9t qu\u1ea3n l\u00fd qu\u1ea3n l\u00fd nh\u00e2n vi\u00ean, m\u1ed9t danh m\u1ee5c ch\u1ee9a c\u00e1c danh m\u1ee5c con, v\u00e0 m\u1ed9t s\u1ea3n ph\u1ea9m c\u00f3 th\u1ec3 l\u00e0 m\u1ed9t ph\u1ea7n c\u1ee7a b\u1ed9 d\u1ee5ng c\u1ee5. Nh\u1eefng t\u00ecnh hu\u1ed1ng n\u00e0y \u0111\u00f2i h\u1ecfi m\u1ed9t m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy.<\/p>\n<p>H\u01b0\u1edbng d\u1eabn n\u00e0y kh\u00e1m ph\u00e1 c\u00e1c c\u01a1 ch\u1ebf, m\u1eabu thi\u1ebft k\u1ebf v\u00e0 c\u00e1c th\u1ef1c h\u00e0nh t\u1ed1t nh\u1ea5t \u0111\u1ec3 x\u1eed l\u00fd c\u00e1c th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n. Ch\u00fang ta s\u1ebd xem x\u00e9t c\u00e1ch c\u1ea5u tr\u00fac c\u00e1c m\u1ed1i quan h\u1ec7 n\u00e0y m\u00e0 kh\u00f4ng ph\u1ee5 thu\u1ed9c v\u00e0o c\u00e1c c\u00f4ng c\u1ee5 ph\u1ea7n m\u1ec1m c\u1ee5 th\u1ec3, t\u1eadp trung v\u00e0o c\u00e1c nguy\u00ean t\u1eafc c\u01a1 s\u1edf d\u1eef li\u1ec7u ph\u1ed5 qu\u00e1t.<\/p>\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter\"><img alt=\"Chalkboard-style educational infographic explaining self-referencing entities and recursive relationships in Entity Relationship Diagrams (ERD), featuring hand-drawn employee hierarchy example with manager_id foreign key looping to employee_id primary key, visual use cases for organizational charts category trees bill of materials and comment threads, key implementation rules including nullable foreign keys indexing and cycle prevention, plus query method comparison between self-joins and recursive CTEs\" decoding=\"async\" src=\"https:\/\/www.go-diagram.com\/wp-content\/uploads\/2026\/03\/self-referencing-entities-erd-chalkboard-infographic.jpg\"\/><\/figure>\n<\/div>\n<h2>\ud83e\uddd0 Th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n l\u00e0 g\u00ec?<\/h2>\n<p>M\u1ed9t th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n x\u1ea3y ra khi m\u1ed9t kh\u00f3a ngo\u1ea1i trong m\u1ed9t b\u1ea3ng tr\u1ecf \u0111\u1ebfn kh\u00f3a ch\u00ednh c\u1ee7a ch\u00ednh b\u1ea3ng \u0111\u00f3. \u0110i\u1ec1u n\u00e0y t\u1ea1o ra m\u1ed9t v\u00f2ng l\u1eb7p n\u01a1i c\u00e1c h\u00e0ng d\u1eef li\u1ec7u trong m\u1ed9t b\u1ea3ng duy nh\u1ea5t c\u00f3 th\u1ec3 tham chi\u1ebfu \u0111\u1ebfn c\u00e1c h\u00e0ng kh\u00e1c trong ch\u00ednh b\u1ea3ng \u0111\u00f3. \u0110\u00e2y l\u00e0 m\u1ed9t k\u1ef9 thu\u1eadt c\u01a1 b\u1ea3n \u0111\u1ec3 m\u00f4 h\u00ecnh h\u00f3a c\u00e1c c\u1ea5u tr\u00fac d\u1eef li\u1ec7u ph\u00e2n c\u1ea5p.<\/p>\n<p><strong>\u0110\u1eb7c \u0111i\u1ec3m ch\u00ednh:<\/strong><\/p>\n<ul>\n<li><strong>B\u1ea3ng duy nh\u1ea5t:<\/strong> M\u1ed1i quan h\u1ec7 t\u1ed3n t\u1ea1i ho\u00e0n to\u00e0n trong c\u1ea5u tr\u00fac m\u1ed9t b\u1ea3ng duy nh\u1ea5t.<\/li>\n<li><strong>Li\u00ean k\u1ebft cha-con:<\/strong> M\u1ed9t h\u00e0ng \u0111\u00f3ng vai tr\u00f2 cha, trong khi m\u1ed9t h\u00e0ng kh\u00e1c \u0111\u00f3ng vai tr\u00f2 con.<\/li>\n<li><strong>X\u1eed l\u00fd gi\u00e1 tr\u1ecb null:<\/strong> G\u1ed1c c\u1ee7a c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p th\u01b0\u1eddng c\u00f3 gi\u00e1 tr\u1ecb null trong c\u1ed9t kh\u00f3a ngo\u1ea1i.<\/li>\n<li><strong>L\u00f4gic v\u00f2ng tr\u00f2n:<\/strong> C\u1ea7n c\u1ea9n tr\u1ecdng \u0111\u1ec3 tr\u00e1nh c\u00e1c v\u00f2ng l\u1eb7p v\u00f4 h\u1ea1n trong qu\u00e1 tr\u00ecnh truy xu\u1ea5t d\u1eef li\u1ec7u.<\/li>\n<\/ul>\n<h2>\ud83c\udfd7\ufe0f C\u00e1c th\u00e0nh ph\u1ea7n c\u1ed1t l\u00f5i c\u1ee7a m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy<\/h2>\n<p>\u0110\u1ec3 tri\u1ec3n khai m\u1ed1i quan h\u1ec7 n\u00e0y m\u1ed9t c\u00e1ch hi\u1ec7u qu\u1ea3, c\u00e1c th\u00e0nh ph\u1ea7n c\u01a1 s\u1edf d\u1eef li\u1ec7u c\u1ee5 th\u1ec3 ph\u1ea3i \u0111\u01b0\u1ee3c \u0111\u1ed3ng b\u1ed9 h\u00f3a. Thi\u1ebft k\u1ebf l\u01b0\u1ee3c \u0111\u1ed3 ph\u1ee5 thu\u1ed9c r\u1ea5t l\u1edbn v\u00e0o s\u1ef1 t\u01b0\u01a1ng t\u00e1c gi\u1eefa kh\u00f3a ch\u00ednh v\u00e0 kh\u00f3a ngo\u1ea1i.<\/p>\n<h3>\ud83d\udd11 Kh\u00f3a ch\u00ednh<\/h3>\n<p>M\u1ed7i h\u00e0ng trong b\u1ea3ng ph\u1ea3i c\u00f3 m\u1ed9t \u0111\u1ecbnh danh duy nh\u1ea5t. \u0110\u00e2y l\u00e0 \u0111i\u1ec3m neo. Khi m\u1ed9t h\u00e0ng tham chi\u1ebfu \u0111\u1ebfn m\u1ed9t h\u00e0ng kh\u00e1c, n\u00f3 l\u00e0m nh\u01b0 v\u1eady b\u1eb1ng c\u00e1ch l\u01b0u tr\u1eef \u0111\u1ecbnh danh duy nh\u1ea5t c\u1ee7a h\u00e0ng cha.<\/p>\n<ul>\n<li>N\u00f3 ph\u1ea3i \u1ed5n \u0111\u1ecbnh. Vi\u1ec7c thay \u0111\u1ed5i kh\u00f3a ch\u00ednh l\u00e0 m\u1ed9t thao t\u00e1c ph\u1ee9c t\u1ea1p.<\/li>\n<li>N\u00f3 n\u00ean \u0111\u01b0\u1ee3c l\u1eadp ch\u1ec9 m\u1ee5c \u0111\u1ec3 th\u1ef1c hi\u1ec7n tra c\u1ee9u nhanh.<\/li>\n<li>Th\u01b0\u1eddng th\u00ec \u0111\u00e2y l\u00e0 m\u1ed9t s\u1ed1 nguy\u00ean t\u1ef1 t\u0103ng ho\u1eb7c UUID.<\/li>\n<\/ul>\n<h3>\ud83d\udd17 Kh\u00f3a ngo\u1ea1i<\/h3>\n<p>C\u1ed9t kh\u00f3a ngo\u1ea1i n\u1eb1m trong c\u00f9ng m\u1ed9t b\u1ea3ng v\u1edbi kh\u00f3a ch\u00ednh. N\u00f3 l\u01b0u tr\u1eef gi\u00e1 tr\u1ecb kh\u00f3a ch\u00ednh c\u1ee7a h\u00e0ng cha. C\u1ed9t n\u00e0y x\u00e1c \u0111\u1ecbnh h\u01b0\u1edbng c\u1ee7a m\u1ed1i quan h\u1ec7.<\/p>\n<ul>\n<li><strong>Cho ph\u00e9p null:<\/strong>Trong m\u1ed9t c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p, m\u1ee5c c\u1ea5p cao nh\u1ea5t (g\u1ed1c) kh\u00f4ng c\u00f3 cha. Do \u0111\u00f3, c\u1ed9t n\u00e0y ph\u1ea3i cho ph\u00e9p gi\u00e1 tr\u1ecb null.<\/li>\n<li><strong>R\u00e0ng bu\u1ed9c:<\/strong> M\u1ed9t r\u00e0ng bu\u1ed9c kh\u00f3a ngo\u1ea1i \u0111\u1ea3m b\u1ea3o r\u1eb1ng gi\u00e1 tr\u1ecb \u0111\u01b0\u1ee3c l\u01b0u kh\u1edbp v\u1edbi m\u1ed9t kh\u00f3a ch\u00ednh t\u1ed3n t\u1ea1i trong c\u00f9ng b\u1ea3ng.<\/li>\n<li><strong>L\u1eadp ch\u1ec9 m\u1ee5c:<\/strong> M\u1eb7c d\u00f9 kh\u00f4ng ph\u1ea3i l\u00fac n\u00e0o c\u0169ng b\u1eaft bu\u1ed9c, nh\u01b0ng vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c cho c\u1ed9t kh\u00f3a ngo\u1ea1i s\u1ebd l\u00e0m t\u0103ng \u0111\u00e1ng k\u1ec3 t\u1ed1c \u0111\u1ed9 truy v\u1ea5n khi duy\u1ec7t qua c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p.<\/li>\n<\/ul>\n<h2>\ud83d\udcd0 Tr\u1ef1c quan h\u00f3a trong s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3<\/h2>\n<p>Khi v\u1ebd s\u01a1 \u0111\u1ed3 ERD \u0111\u1ec3 bi\u1ec3u di\u1ec5n m\u1ed9t th\u1ef1c th\u1ec3 t\u1ef1 tham chi\u1ebfu, k\u00fd hi\u1ec7u c\u00f3 th\u1ec3 g\u00e2y nh\u1ea7m l\u1eabn khi nh\u00ecn l\u1ea7n \u0111\u1ea7u. C\u00e1c c\u00f4ng c\u1ee5 ERD ti\u00eau chu\u1ea9n s\u1eed d\u1ee5ng c\u00e1c \u0111\u01b0\u1eddng \u0111\u1eb7c bi\u1ec7t \u0111\u1ec3 bi\u1ec3u th\u1ecb m\u1ed1i quan h\u1ec7 k\u1ebft n\u1ed1i.<\/p>\n<p><strong>Quy t\u1eafc k\u00fd hi\u1ec7u tr\u1ef1c quan:<\/strong><\/p>\n<ul>\n<li>H\u1ed9p th\u1ef1c th\u1ec3 \u0111\u01b0\u1ee3c v\u1ebd m\u1ed9t l\u1ea7n.<\/li>\n<li>\u0110\u01b0\u1eddng m\u1ed1i quan h\u1ec7 n\u1ed1i kh\u00f3a ch\u00ednh v\u1edbi kh\u00f3a ngo\u1ea1i b\u00ean trong c\u00f9ng m\u1ed9t h\u1ed9p.<\/li>\n<li>\u0110\u01b0\u1eddng th\u01b0\u1eddng quay tr\u1edf l\u1ea1i th\u1ef1c th\u1ec3, t\u1ea1o th\u00e0nh m\u1ed9t v\u00f2ng tr\u00f2n tr\u1ef1c quan.<\/li>\n<li>C\u00e1c k\u00fd hi\u1ec7u cardinality (1:1, 1:M) \u0111\u01b0\u1ee3c \u0111\u1eb7t tr\u00ean \u0111\u01b0\u1eddng \u0111\u1ec3 ch\u1ec9 s\u1ed1 l\u01b0\u1ee3ng con m\u00e0 m\u1ed9t cha c\u00f3 th\u1ec3 c\u00f3.<\/li>\n<\/ul>\n<p><strong>V\u00ed d\u1ee5: C\u1ea5u tr\u00fac t\u1ed5 ch\u1ee9c<\/strong><\/p>\n<table border=\"1\" cellpadding=\"5\" cellspacing=\"0\">\n<thead>\n<tr>\n<th>Kh\u00e1i ni\u1ec7m<\/th>\n<th>M\u00f4 t\u1ea3<\/th>\n<th>K\u00fd hi\u1ec7u ERD<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Nh\u00e2n vi\u00ean<\/td>\n<td>Th\u1ef1c th\u1ec3 \u0111ang \u0111\u01b0\u1ee3c m\u00f4 h\u00ecnh h\u00f3a<\/td>\n<td>H\u1ed9p \u0111\u01b0\u1ee3c ghi nh\u00e3n &#8220;Nh\u00e2n vi\u00ean&#8221;<\/td>\n<\/tr>\n<tr>\n<td>Qu\u1ea3n l\u00fd<\/td>\n<td>Vai tr\u00f2 tham chi\u1ebfu \u0111\u1ebfn c\u00f9ng m\u1ed9t b\u1ea3ng<\/td>\n<td>\u0110\u01b0\u1eddng t\u1eeb ID Qu\u1ea3n l\u00fd \u0111\u1ebfn ID Nh\u00e2n vi\u00ean<\/td>\n<\/tr>\n<tr>\n<td>\u0110\u01b0\u1eddng b\u00e1o c\u00e1o<\/td>\n<td>M\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy<\/td>\n<td>M\u0169i t\u00ean v\u00f2ng l\u1eb7p<\/td>\n<\/tr>\n<tr>\n<td>N\u00fat g\u1ed1c<\/td>\n<td>CEO ho\u1eb7c c\u1ea5p tr\u00ean cao nh\u1ea5t<\/td>\n<td>Gi\u00e1 tr\u1ecb r\u1ed7ng trong ID Qu\u1ea3n l\u00fd<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>\ud83c\udf33 C\u00e1c tr\u01b0\u1eddng h\u1ee3p s\u1eed d\u1ee5ng ph\u1ed5 bi\u1ebfn cho d\u1eef li\u1ec7u \u0111\u1ec7 quy<\/h2>\n<p>C\u00e1c m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy kh\u00f4ng ph\u1ea3i l\u00e0 l\u00fd thuy\u1ebft; ch\u00fang gi\u1ea3i quy\u1ebft c\u00e1c v\u1ea5n \u0111\u1ec1 th\u1ef1c t\u1ebf trong m\u00f4 h\u00ecnh h\u00f3a d\u1eef li\u1ec7u. D\u01b0\u1edbi \u0111\u00e2y l\u00e0 nh\u1eefng t\u00ecnh hu\u1ed1ng ph\u1ed5 bi\u1ebfn nh\u1ea5t m\u00e0 m\u1eabu n\u00e0y \u0111\u01b0\u1ee3c \u00e1p d\u1ee5ng.<\/p>\n<h3>1\ufe0f\u20e3 C\u00e1c c\u1ea5p b\u1eadc t\u1ed5 ch\u1ee9c<\/h3>\n<p>M\u1ed7i c\u00f4ng ty \u0111\u1ec1u c\u00f3 c\u1ea5u tr\u00fac. Nh\u00e2n vi\u00ean b\u00e1o c\u00e1o cho qu\u1ea3n l\u00fd, ng\u01b0\u1eddi qu\u1ea3n l\u00fd b\u00e1o c\u00e1o cho gi\u00e1m \u0111\u1ed1c, ng\u01b0\u1eddi gi\u00e1m \u0111\u1ed1c b\u00e1o c\u00e1o cho c\u00e1c ph\u00f3 gi\u00e1m \u0111\u1ed1c. Chu\u1ed7i n\u00e0y l\u00e0 m\u1ed9t c\u1ea5u tr\u00fac c\u00e2y kinh \u0111i\u1ec3n.<\/p>\n<ul>\n<li><strong>M\u00f4 h\u00ecnh d\u1eef li\u1ec7u:<\/strong> M\u1ed9t b\u1ea3ng c\u00f3 t\u00ean l\u00e0 &#8220;Nh\u00e2n vi\u00ean&#8221;.<\/li>\n<li><strong>C\u00e1c c\u1ed9t:<\/strong> <code>employee_id<\/code>, <code>name<\/code>, <code>manager_id<\/code>.<\/li>\n<li><strong>Logic:<\/strong> The <code>manager_id<\/code> c\u1ed9t tham chi\u1ebfu <code>employee_id<\/code>.<\/li>\n<li><strong>L\u1ee3i \u00edch:<\/strong> Vi\u1ec7c th\u00eam nh\u00e2n vi\u00ean m\u1edbi ch\u1ec9 y\u00eau c\u1ea7u ch\u00e8n m\u1ed9t h\u00e0ng. Kh\u00f4ng c\u1ea7n t\u1ea1o b\u1ea3ng m\u1edbi cho t\u1eebng ph\u00f2ng ban.<\/li>\n<\/ul>\n<h3>2\ufe0f\u20e3 C\u00e2y danh m\u1ee5c<\/h3>\n<p>C\u00e1c n\u1ec1n t\u1ea3ng th\u01b0\u01a1ng m\u1ea1i \u0111i\u1ec7n t\u1eed th\u01b0\u1eddng s\u1eafp x\u1ebfp s\u1ea3n ph\u1ea9m th\u00e0nh c\u00e1c danh m\u1ee5c l\u1ed3ng gh\u00e9p. \u0110i\u1ec7n t\u1eed &gt; M\u00e1y t\u00ednh &gt; Laptop.<\/p>\n<ul>\n<li><strong>M\u00f4 h\u00ecnh d\u1eef li\u1ec7u:<\/strong> M\u1ed9t b\u1ea3ng c\u00f3 t\u00ean l\u00e0 &#8220;Categories&#8221;.<\/li>\n<li><strong>C\u00e1c c\u1ed9t:<\/strong> <code>category_id<\/code>, <code>name<\/code>, <code>parent_id<\/code>.<\/li>\n<li><strong>Logic:<\/strong> M\u1ed9t danh m\u1ee5c c\u00f3 th\u1ec3 c\u00f3 danh m\u1ee5c cha, ho\u1eb7c n\u00f3 c\u00f3 th\u1ec3 l\u00e0 danh m\u1ee5c g\u1ed1c (parent_id l\u00e0 null).<\/li>\n<li><strong>L\u1ee3i \u00edch:<\/strong> Linh ho\u1ea1t \u0111\u1ec3 th\u00eam b\u1ea5t k\u1ef3 s\u1ed1 l\u01b0\u1ee3ng danh m\u1ee5c con n\u00e0o c\u1ea7n thi\u1ebft m\u00e0 kh\u00f4ng c\u1ea7n thay \u0111\u1ed5i c\u1ea5u tr\u00fac b\u1ea3ng.<\/li>\n<\/ul>\n<h3>3\ufe0f\u20e3 Danh s\u00e1ch v\u1eadt li\u1ec7u (BOM)<\/h3>\n<p>S\u1ea3n xu\u1ea5t th\u01b0\u1eddng \u0111\u00f2i h\u1ecfi danh s\u00e1ch chi ti\u1ebft ph\u1ee9c t\u1ea1p. M\u1ed9t chi\u1ebfc xe \u0111\u01b0\u1ee3c t\u1ea1o n\u00ean t\u1eeb \u0111\u1ed9ng c\u01a1, m\u00e0 \u0111\u1ed9ng c\u01a1 l\u1ea1i \u0111\u01b0\u1ee3c t\u1ea1o n\u00ean t\u1eeb p\u00edt-t\u00f4ng. \u0110\u00f4i khi m\u1ed9t p\u00edt-t\u00f4ng l\u00e0 m\u1ed9t ph\u1ea7n c\u1ee7a lo\u1ea1i \u0111\u1ed9ng c\u01a1 kh\u00e1c.<\/p>\n<ul>\n<li><strong>M\u00f4 h\u00ecnh d\u1eef li\u1ec7u:<\/strong> M\u1ed9t b\u1ea3ng c\u00f3 t\u00ean l\u00e0 &#8220;Parts&#8221;.<\/li>\n<li><strong>C\u1ed9t:<\/strong> <code>part_id<\/code>, <code>m\u00f4 t\u1ea3<\/code>, <code>assembly_id<\/code>.<\/li>\n<li><strong>Logic:<\/strong> M\u1ed9t b\u1ed9 ph\u1eadn c\u00f3 th\u1ec3 l\u00e0 m\u1ed9t b\u1ed9 l\u1eafp r\u00e1p ri\u00eang bi\u1ec7t, ch\u1ee9a c\u00e1c b\u1ed9 ph\u1eadn kh\u00e1c.<\/li>\n<li><strong>L\u1ee3i \u00edch:<\/strong> Cho ph\u00e9p c\u1ea5u tr\u00fac s\u1ea3n xu\u1ea5t \u0111a c\u1ea5p.<\/li>\n<\/ul>\n<h3>4\ufe0f\u20e3 Chu\u1ed7i b\u00ecnh lu\u1eadn<\/h3>\n<p>C\u00e1c di\u1ec5n \u0111\u00e0n v\u00e0 blog cho ph\u00e9p ng\u01b0\u1eddi d\u00f9ng tr\u1ea3 l\u1eddi b\u00ecnh lu\u1eadn. M\u1ed9t b\u00ecnh lu\u1eadn c\u00f3 th\u1ec3 c\u00f3 m\u1ed9t b\u00ecnh lu\u1eadn cha m\u00e0 n\u00f3 \u0111ang tr\u1ea3 l\u1eddi, ho\u1eb7c c\u00f3 th\u1ec3 l\u00e0 m\u1ed9t b\u00ecnh lu\u1eadn \u0111\u1ed9c l\u1eadp.<\/p>\n<ul>\n<li><strong>M\u00f4 h\u00ecnh d\u1eef li\u1ec7u:<\/strong> M\u1ed9t b\u1ea3ng c\u00f3 t\u00ean l\u00e0 &#8220;Comments&#8221;.<\/li>\n<li><strong>C\u1ed9t:<\/strong> <code>comment_id<\/code>, <code>user_id<\/code>, <code>n\u1ed9i dung<\/code>, <code>parent_comment_id<\/code>.<\/li>\n<li><strong>Logic:<\/strong> M\u1ed9t ph\u1ea3n h\u1ed3i li\u00ean k\u1ebft tr\u1edf l\u1ea1i ID b\u00ecnh lu\u1eadn g\u1ed1c.<\/li>\n<li><strong>L\u1ee3i \u00edch:<\/strong> H\u1ed7 tr\u1ee3 l\u1ed3ng gh\u00e9p v\u00f4 h\u1ea1n c\u00e1c cu\u1ed9c th\u1ea3o lu\u1eadn.<\/li>\n<\/ul>\n<h2>\u2699\ufe0f C\u00e1c c\u00e2n nh\u1eafc khi tri\u1ec3n khai<\/h2>\n<p>Thi\u1ebft k\u1ebf l\u01b0\u1ee3c \u0111\u1ed3 ch\u1ec9 l\u00e0 b\u01b0\u1edbc \u0111\u1ea7u ti\u00ean. \u0110\u1ea3m b\u1ea3o d\u1eef li\u1ec7u ho\u1ea1t \u0111\u1ed9ng \u0111\u00fang trong c\u00e1c \u0111i\u1ec1u ki\u1ec7n kh\u00e1c nhau \u0111\u00f2i h\u1ecfi s\u1ef1 l\u00ean k\u1ebf ho\u1ea1ch c\u1ea9n th\u1eadn.<\/p>\n<h3>\ud83d\uded1 Ng\u0103n ch\u1eb7n tham chi\u1ebfu v\u00f2ng<\/h3>\n<p>M\u1ed9t r\u1ee7i ro nghi\u00eam tr\u1ecdng trong c\u00e1c m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy l\u00e0 t\u1ea1o ra chu k\u1ef3. V\u00ed d\u1ee5, Nh\u00e2n vi\u00ean A qu\u1ea3n l\u00fd Nh\u00e2n vi\u00ean B, v\u00e0 Nh\u00e2n vi\u00ean B qu\u1ea3n l\u00fd Nh\u00e2n vi\u00ean A. \u0110i\u1ec1u n\u00e0y t\u1ea1o ra m\u1ed9t v\u00f2ng l\u1eb7p v\u00f4 h\u1ea1n.<\/p>\n<ul>\n<li><strong>Logic \u1ee9ng d\u1ee5ng:<\/strong> Khi ch\u00e8n ho\u1eb7c c\u1eadp nh\u1eadt d\u1eef li\u1ec7u, \u1ee9ng d\u1ee5ng n\u00ean x\u00e1c minh \u0111\u1ed9 s\u00e2u c\u1ee7a c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o kh\u00f4ng t\u1ea1o ra chu k\u1ef3.<\/li>\n<li><strong>R\u00e0ng bu\u1ed9c c\u01a1 s\u1edf d\u1eef li\u1ec7u:<\/strong> M\u1eb7c d\u00f9 c\u00e1c r\u00e0ng bu\u1ed9c SQL th\u00f4ng th\u01b0\u1eddng kh\u00f4ng th\u1ec3 d\u1ec5 d\u00e0ng ng\u0103n ch\u1eb7n chu k\u1ef3 (v\u00ec ch\u00fang ki\u1ec3m tra tr\u1ea1ng th\u00e1i hi\u1ec7n t\u1ea1i, ch\u1ee9 kh\u00f4ng ph\u1ea3i tr\u1ea1ng th\u00e1i k\u1ebft qu\u1ea3), c\u00e1c trigger c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng trong m\u1ed9t s\u1ed1 h\u1ec7 th\u1ed1ng \u0111\u1ec3 x\u00e1c th\u1ef1c \u0111\u01b0\u1eddng \u0111i tr\u01b0\u1edbc khi ghi d\u1eef li\u1ec7u.<\/li>\n<li><strong>X\u00e1c \u0111\u1ecbnh n\u00fat g\u1ed1c:<\/strong> \u0110\u1ea3m b\u1ea3o m\u1ed7i c\u00e2y h\u1ee3p l\u1ec7 ch\u1ec9 c\u00f3 \u0111\u00fang m\u1ed9t n\u00fat g\u1ed1c (n\u01a1i kh\u00f3a ngo\u1ea1i l\u00e0 null).<\/li>\n<\/ul>\n<h3>\ud83d\udcc9 X\u1eed l\u00fd gi\u00e1 tr\u1ecb null<\/h3>\n<p>N\u00fat g\u1ed1c c\u1ee7a c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p l\u00e0 \u0111i\u1ec3m b\u1eaft \u0111\u1ea7u. Trong m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy ti\u00eau chu\u1ea9n, h\u00e0ng g\u1ed1c c\u00f3 gi\u00e1 tr\u1ecb null trong c\u1ed9t kh\u00f3a ngo\u1ea1i.<\/p>\n<ul>\n<li><strong>Truy v\u1ea5n:<\/strong> \u0110\u1ec3 t\u00ecm t\u1ea5t c\u1ea3 c\u00e1c n\u00fat g\u1ed1c, truy v\u1ea5n c\u00e1c h\u00e0ng m\u00e0 kh\u00f3a ngo\u1ea1i l\u00e0 NULL.<\/li>\n<li><strong>Gi\u00e1 tr\u1ecb m\u1eb7c \u0111\u1ecbnh:<\/strong> Kh\u00f4ng \u0111\u1eb7t gi\u00e1 tr\u1ecb m\u1eb7c \u0111\u1ecbnh cho kh\u00f3a ngo\u1ea1i n\u1ebfu n\u00f3 ng\u1ee5 \u00fd m\u1ed9t n\u00fat cha. Gi\u00e1 tr\u1ecb m\u1eb7c \u0111\u1ecbnh l\u00e0 0 ho\u1eb7c -1 c\u00f3 th\u1ec3 g\u00e2y hi\u1ec3u l\u1ea7m v\u00e0 d\u1eabn \u0111\u1ebfn v\u1ea5n \u0111\u1ec1 to\u00e0n v\u1eb9n d\u1eef li\u1ec7u.<\/li>\n<li><strong>To\u00e0n v\u1eb9n:<\/strong> \u0110\u1ea3m b\u1ea3o b\u1ed9 \u0111\u1ed9ng c\u01a1 c\u01a1 s\u1edf d\u1eef li\u1ec7u cho ph\u00e9p gi\u00e1 tr\u1ecb NULL cho c\u1ed9t kh\u00f3a ngo\u1ea1i. R\u00e0ng bu\u1ed9c NOT NULL s\u1ebd ph\u00e1 v\u1ee1 m\u00f4 h\u00ecnh ph\u00e2n c\u1ea5p.<\/li>\n<\/ul>\n<h3>\ud83d\udcc8 Hi\u1ec7u su\u1ea5t v\u00e0 ch\u1ec9 m\u1ee5c<\/h3>\n<p>Khi d\u1eef li\u1ec7u t\u0103ng l\u00ean, truy v\u1ea5n c\u00e1c c\u1ea5u tr\u00fac \u0111\u1ec7 quy c\u00f3 th\u1ec3 tr\u1edf n\u00ean ch\u1eadm. M\u1ed9t truy v\u1ea5n \u0111\u01a1n gi\u1ea3n \u0111\u1ec3 t\u00ecm t\u1ea5t c\u1ea3 c\u00e1c n\u00fat con c\u1ee7a m\u1ed9t n\u00fat c\u1ee5 th\u1ec3 c\u00f3 th\u1ec3 y\u00eau c\u1ea7u nhi\u1ec1u ph\u00e9p n\u1ed1i ho\u1eb7c truy v\u1ea5n \u0111\u1ec7 quy.<\/p>\n<p><strong>Chi\u1ebfn l\u01b0\u1ee3c t\u1ed1i \u01b0u h\u00f3a:<\/strong><\/p>\n<ul>\n<li><strong>Ch\u1ec9 m\u1ee5c kh\u00f3a ngo\u1ea1i:<\/strong> T\u1ea1o ch\u1ec9 m\u1ee5c tr\u00ean c\u1ed9t l\u01b0u tham chi\u1ebfu \u0111\u1ebfn n\u00fat cha. \u0110i\u1ec1u n\u00e0y gi\u00fap t\u0103ng t\u1ed1c \u0111\u1ed9 t\u00ecm ki\u1ebfm c\u00e1c n\u00fat con.<\/li>\n<li><strong>\u0110\u01b0\u1eddng \u0111i \u0111\u01b0\u1ee3c v\u1eadt ch\u1ea5t h\u00f3a:<\/strong> M\u1ed9t s\u1ed1 h\u1ec7 th\u1ed1ng l\u01b0u to\u00e0n b\u1ed9 \u0111\u01b0\u1eddng \u0111i c\u1ee7a c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p trong m\u1ed9t c\u1ed9t ri\u00eang bi\u1ec7t (v\u00ed d\u1ee5: &#8220;\/1\/5\/12\/20&#8221;). \u0110i\u1ec1u n\u00e0y cho ph\u00e9p l\u1ecdc nhanh d\u1ef1a tr\u00ean chu\u1ed7i, m\u1eb7c d\u00f9 y\u00eau c\u1ea7u c\u1eadp nh\u1eadt m\u1ed7i khi ch\u00e8n d\u1eef li\u1ec7u m\u1edbi.<\/li>\n<li><strong>T\u1eadp h\u1ee3p l\u1ed3ng gh\u00e9p:<\/strong> M\u1ed9t thu\u1eadt to\u00e1n thay th\u1ebf s\u1eed d\u1ee5ng c\u00e1c s\u1ed1 tr\u00e1i v\u00e0 ph\u1ea3i \u0111\u1ec3 bi\u1ec3u di\u1ec5n \u0111\u1ed9 s\u00e2u. Ph\u01b0\u01a1ng ph\u00e1p n\u00e0y nhanh h\u01a1n khi truy xu\u1ea5t nh\u01b0ng ch\u1eadm h\u01a1n khi ch\u00e8n.<\/li>\n<li><strong>\u0110\u1ed9 s\u00e2u truy v\u1ea5n:<\/strong> Gi\u1edbi h\u1ea1n \u0111\u1ed9 s\u00e2u \u0111\u1ec7 quy trong c\u00e1c truy v\u1ea5n c\u1ee7a b\u1ea1n. C\u00e1c v\u00f2ng l\u1eb7p v\u00f4 h\u1ea1n c\u00f3 th\u1ec3 khi\u1ebfn b\u1ed9 \u0111\u1ed9ng c\u01a1 c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1eadp n\u1ebfu kh\u00f4ng \u0111\u01b0\u1ee3c gi\u1edbi h\u1ea1n.<\/li>\n<\/ul>\n<h2>\ud83d\udd0d Truy v\u1ea5n d\u1eef li\u1ec7u \u0111\u1ec7 quy<\/h2>\n<p>Vi\u1ec7c truy xu\u1ea5t d\u1eef li\u1ec7u ph\u00e2n c\u1ea5p ph\u1ee9c t\u1ea1p h\u01a1n so v\u1edbi truy xu\u1ea5t d\u1eef li\u1ec7u ph\u1eb3ng. C\u00e1c JOIN ti\u00eau chu\u1ea9n ho\u1ea1t \u0111\u1ed9ng t\u1ed1t cho m\u1ed9t c\u1ea5p, nh\u01b0ng nhi\u1ec1u c\u1ea5p c\u1ea7n logic chuy\u00ean bi\u1ec7t.<\/p>\n<h3>\ud83d\udd04 T\u1ef1 JOIN<\/h3>\n<p>Ph\u01b0\u01a1ng ph\u00e1p ph\u1ed5 bi\u1ebfn nh\u1ea5t bao g\u1ed3m vi\u1ec7c JOIN b\u1ea3ng v\u1edbi ch\u00ednh n\u00f3. B\u1ea1n \u0111\u1eb7t bi\u1ec7t danh cho b\u1ea3ng m\u1ed9t l\u1ea7n l\u00e0 cha v\u00e0 m\u1ed9t l\u1ea7n l\u00e0 con.<\/p>\n<ul>\n<li><strong>M\u1ed9t c\u1ea5p:<\/strong>JOIN b\u1ea3ng v\u1edbi ch\u00ednh n\u00f3 m\u1ed9t l\u1ea7n \u0111\u1ec3 l\u1ea5y cha ngay l\u1eadp t\u1ee9c.<\/li>\n<li><strong>Nhi\u1ec1u c\u1ea5p:<\/strong>Y\u00eau c\u1ea7u nhi\u1ec1u JOIN, \u0111i\u1ec1u n\u00e0y nhanh ch\u00f3ng tr\u1edf n\u00ean kh\u00f3 qu\u1ea3n l\u00fd.<\/li>\n<li><strong>Nh\u01b0\u1ee3c \u0111i\u1ec3m:<\/strong>S\u1ed1 l\u01b0\u1ee3ng JOIN c\u1ea7n thi\u1ebft b\u1eb1ng v\u1edbi \u0111\u1ed9 s\u00e2u c\u1ee7a c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p.<\/li>\n<\/ul>\n<h3>\ud83d\udd01 Bi\u1ec3u th\u1ee9c CTE \u0111\u1ec7 quy<\/h3>\n<p>C\u00e1c h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u hi\u1ec7n \u0111\u1ea1i h\u1ed7 tr\u1ee3 CTE \u0111\u1ec7 quy. \u0110i\u1ec1u n\u00e0y cho ph\u00e9p m\u1ed9t truy v\u1ea5n th\u1ef1c hi\u1ec7n UNION ALL v\u1edbi ch\u00ednh n\u00f3 cho \u0111\u1ebfn khi kh\u00f4ng c\u00f2n d\u00f2ng n\u00e0o ph\u00f9 h\u1ee3p.<\/p>\n<ul>\n<li><strong>Th\u00e0nh vi\u00ean g\u1ed1c:<\/strong>\u0110i\u1ec3m kh\u1edfi \u0111\u1ea7u c\u1ee7a \u0111\u1ec7 quy (th\u01b0\u1eddng l\u00e0 n\u00fat g\u1ed1c).<\/li>\n<li><strong>Th\u00e0nh vi\u00ean \u0111\u1ec7 quy:<\/strong>Ph\u1ea7n truy v\u1ea5n k\u1ebft n\u1ed1i k\u1ebft qu\u1ea3 tr\u1edf l\u1ea1i b\u1ea3ng \u0111\u1ec3 t\u00ecm c\u1ea5p ti\u1ebfp theo.<\/li>\n<li><strong>K\u1ebft th\u00fac:<\/strong>Truy v\u1ea5n d\u1eebng l\u1ea1i khi kh\u00f4ng c\u00f2n d\u00f2ng n\u00e0o ph\u00f9 h\u1ee3p \u0111\u01b0\u1ee3c t\u00ecm th\u1ea5y.<\/li>\n<li><strong>L\u1ee3i \u00edch:<\/strong>X\u1eed l\u00fd b\u1ea5t k\u1ef3 \u0111\u1ed9 s\u00e2u n\u00e0o c\u1ee7a c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p m\u00e0 kh\u00f4ng c\u1ea7n bi\u1ebft tr\u01b0\u1edbc.<\/li>\n<\/ul>\n<h2>\ud83d\udee1\ufe0f B\u1ea3o to\u00e0n to\u00e0n v\u1eb9n d\u1eef li\u1ec7u v\u00e0 r\u00e0ng bu\u1ed9c<\/h2>\n<p>Duy tr\u00ec to\u00e0n v\u1eb9n c\u1ee7a b\u1ea3ng tham chi\u1ebfu t\u1ef1 th\u00e2n l\u00e0 r\u1ea5t quan tr\u1ecdng. N\u1ebfu m\u1ed9t n\u00fat cha b\u1ecb x\u00f3a, c\u00e1c n\u00fat con s\u1ebd ra sao?<\/p>\n<h3>\ud83d\uddd1\ufe0f X\u00f3a lan truy\u1ec1n<\/h3>\n<p>Khi m\u1ed9t h\u00e0ng cha b\u1ecb x\u00f3a, c\u01a1 s\u1edf d\u1eef li\u1ec7u ph\u1ea3i quy\u1ebft \u0111\u1ecbnh x\u1eed l\u00fd c\u00e1c h\u00e0ng con nh\u01b0 th\u1ebf n\u00e0o.<\/p>\n<ul>\n<li><strong>RESTRICT:<\/strong>Ng\u0103n vi\u1ec7c x\u00f3a n\u00fat cha n\u1ebfu t\u1ed3n t\u1ea1i c\u00e1c n\u00fat con. \u0110i\u1ec1u n\u00e0y b\u1ea3o to\u00e0n d\u1eef li\u1ec7u nh\u01b0ng c\u00f3 th\u1ec3 c\u1ea3n tr\u1edf vi\u1ec7c d\u1ecdn d\u1eb9p c\u1ea7n thi\u1ebft.<\/li>\n<li><strong>CASCADE:<\/strong>X\u00f3a t\u1ea5t c\u1ea3 c\u00e1c h\u00e0ng con khi n\u00fat cha b\u1ecb x\u00f3a. \u0110i\u1ec1u n\u00e0y nguy hi\u1ec3m trong c\u00e1c c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p s\u00e2u v\u00ec c\u00f3 th\u1ec3 x\u00f3a v\u00f4 t\u00ecnh m\u1ed9t ph\u1ea7n l\u1edbn d\u1eef li\u1ec7u.<\/li>\n<li><strong>SET NULL:<\/strong>Thi\u1ebft l\u1eadp kh\u00f3a ngo\u1ea1i c\u1ee7a c\u00e1c n\u00fat con th\u00e0nh NULL, bi\u1ebfn ch\u00fang th\u00e0nh n\u00fat g\u1ed1c m\u1edbi. \u0110\u00e2y th\u01b0\u1eddng l\u00e0 l\u1ef1a ch\u1ecdn an to\u00e0n nh\u1ea5t \u0111\u1ec3 b\u1ea3o to\u00e0n c\u1ea5u tr\u00fac d\u1eef li\u1ec7u.<\/li>\n<li><strong>THI\u1ebeT L\u1eacP M\u1eb6C \u0110\u1ecaNH:<\/strong>Thi\u1ebft l\u1eadp kh\u00f3a ngo\u1ea1i th\u00e0nh gi\u00e1 tr\u1ecb m\u1eb7c \u0111\u1ecbnh (v\u00ed d\u1ee5: m\u1ed9t danh m\u1ee5c m\u1ed3 c\u00f4i c\u1ee5 th\u1ec3).<\/li>\n<\/ul>\n<h3>\ud83d\udd12 R\u00e0ng bu\u1ed9c c\u1eadp nh\u1eadt<\/h3>\n<p>Thay \u0111\u1ed5i kh\u00f3a ch\u00ednh c\u1ee7a m\u1ed9t h\u00e0ng cha l\u00e0 r\u1ee7i ro. N\u1ebfu b\u1ea1n thay \u0111\u1ed5i ID c\u1ee7a m\u1ed9t qu\u1ea3n l\u00fd, b\u1ea1n ph\u1ea3i c\u1eadp nh\u1eadt ID \u0111\u00f3 trong m\u1ecdi b\u1ea3n ghi nh\u00e2n vi\u00ean tham chi\u1ebfu \u0111\u1ebfn h\u1ecd.<\/p>\n<ul>\n<li><strong>L\u1edbp \u1ee8ng d\u1ee5ng:<\/strong>X\u1eed l\u00fd c\u1eadp nh\u1eadt theo giao d\u1ecbch \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o t\u1ea5t c\u1ea3 c\u00e1c tham chi\u1ebfu \u0111\u01b0\u1ee3c c\u1eadp nh\u1eadt c\u00f9ng nhau.<\/li>\n<li><strong>B\u1ed9 k\u00edch ho\u1ea1t C\u01a1 s\u1edf d\u1eef li\u1ec7u:<\/strong>C\u00f3 th\u1ec3 t\u1ef1 \u0111\u1ed9ng h\u00f3a vi\u1ec7c lan truy\u1ec1n thay \u0111\u1ed5i ID, m\u1eb7c d\u00f9 \u0111i\u1ec1u n\u00e0y l\u00e0m t\u0103ng \u0111\u1ed9 ph\u1ee9c t\u1ea1p.<\/li>\n<li><strong>Th\u1ef1c h\u00e0nh T\u1ed1t nh\u1ea5t:<\/strong>Tr\u00e1nh c\u1eadp nh\u1eadt kh\u00f3a ch\u00ednh trong c\u00e1c c\u1ea5u tr\u00fac \u0111\u1ec7 quy m\u1ed7i khi c\u00f3 th\u1ec3. S\u1eed d\u1ee5ng kh\u00f3a gi\u1ea3 (s\u1ed1 nguy\u00ean t\u1ef1 t\u0103ng) thay v\u00ec kh\u00f3a t\u1ef1 nhi\u00ean (nh\u01b0 m\u00e3 nh\u00e2n vi\u00ean).<\/li>\n<\/ul>\n<h2>\ud83d\udea7 Kh\u1eafc ph\u1ee5c c\u00e1c v\u1ea5n \u0111\u1ec1 ph\u1ed5 bi\u1ebfn<\/h2>\n<p>Ngay c\u1ea3 v\u1edbi thi\u1ebft k\u1ebf c\u1ea9n th\u1eadn, c\u00e1c v\u1ea5n \u0111\u1ec1 v\u1eabn c\u00f3 th\u1ec3 ph\u00e1t sinh trong qu\u00e1 tr\u00ecnh ph\u00e1t tri\u1ec3n v\u00e0 b\u1ea3o tr\u00ec.<\/p>\n<h3>\u2753 L\u00e0m th\u1ebf n\u00e0o \u0111\u1ec3 t\u00ecm \u0111\u1ed9 s\u00e2u c\u1ee7a m\u1ed9t c\u00e2y?<\/h3>\n<p>\u0110\u1ec3 x\u00e1c \u0111\u1ecbnh c\u1ea5p \u0111\u1ed9 c\u1ee7a m\u1ed9t h\u00e0ng c\u1ee5 th\u1ec3, b\u1ea1n ph\u1ea3i \u0111i l\u00ean t\u1eeb h\u00e0ng \u0111\u00f3 \u0111\u1ebfn g\u1ed1c. \u0110\u1ebfm s\u1ed1 l\u1ea7n nh\u1ea3y.<\/p>\n<ul>\n<li><strong>Ph\u01b0\u01a1ng ph\u00e1p Truy v\u1ea5n:<\/strong>S\u1eed d\u1ee5ng truy v\u1ea5n \u0111\u1ec7 quy \u0111\u1ebfm c\u00e1c h\u00e0ng khi di chuy\u1ec3n l\u00ean tr\u00ean.<\/li>\n<li><strong>Ph\u01b0\u01a1ng ph\u00e1p \u1ee8ng d\u1ee5ng:<\/strong>L\u01b0u \u0111\u1ed9 s\u00e2u v\u00e0o m\u1ed9t c\u1ed9t trong qu\u00e1 tr\u00ecnh ch\u00e8n. \u0110i\u1ec1u n\u00e0y ti\u1ebft ki\u1ec7m th\u1eddi gian truy v\u1ea5n nh\u01b0ng \u0111\u00f2i h\u1ecfi b\u1ea3o tr\u00ec.<\/li>\n<\/ul>\n<h3>\u2753 L\u00e0m th\u1ebf n\u00e0o \u0111\u1ec3 x\u1eed l\u00fd c\u00e1c n\u00fat m\u1ed3 c\u00f4i?<\/h3>\n<p>C\u00e1c n\u00fat m\u1ed3 c\u00f4i l\u00e0 c\u00e1c h\u00e0ng m\u00e0 kh\u00f3a ngo\u1ea1i tr\u1ecf \u0111\u1ebfn m\u1ed9t cha kh\u00f4ng t\u1ed3n t\u1ea1i. \u0110i\u1ec1u n\u00e0y th\u01b0\u1eddng x\u1ea3y ra do l\u1ed7i ph\u1ea7n m\u1ec1m ho\u1eb7c l\u1ed7i nh\u1eadp li\u1ec7u th\u1ee7 c\u00f4ng.<\/p>\n<ul>\n<li><strong>X\u00e1c th\u1ef1c:<\/strong>Ch\u1ea1y ki\u1ec3m tra to\u00e0n v\u1eb9n \u0111\u1ecbnh k\u1ef3 \u0111\u1ec3 t\u00ecm c\u00e1c h\u00e0ng m\u00e0 kh\u00f3a ngo\u1ea1i kh\u00f4ng kh\u1edbp v\u1edbi b\u1ea5t k\u1ef3 kh\u00f3a ch\u00ednh n\u00e0o.<\/li>\n<li><strong>Ph\u1ee5c h\u1ed3i:<\/strong>X\u00e1c \u0111\u1ecbnh ch\u00ednh s\u00e1ch: di chuy\u1ec3n ch\u00fang \u0111\u1ebfn danh m\u1ee5c g\u1ed1c, x\u00f3a ch\u00fang, ho\u1eb7c \u0111\u00e1nh d\u1ea5u \u0111\u1ec3 xem x\u00e9t.<\/li>\n<\/ul>\n<h3>\u2753 Suy gi\u1ea3m hi\u1ec7u su\u1ea5t theo th\u1eddi gian<\/h3>\n<p>Khi c\u00e2y ph\u00e1t tri\u1ec3n, c\u00e1c truy v\u1ea5n qu\u00e9t to\u00e0n b\u1ed9 c\u00e2y tr\u1edf n\u00ean ch\u1eadm h\u01a1n.<\/p>\n<ul>\n<li><strong>L\u01b0u tr\u1eef t\u1ea1m:<\/strong>L\u01b0u tr\u1eef t\u1ea1m c\u00e1c c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p th\u01b0\u1eddng \u0111\u01b0\u1ee3c truy c\u1eadp trong b\u1ed9 nh\u1edb \u1ee9ng d\u1ee5ng.<\/li>\n<li><strong>L\u01b0u tr\u1eef:<\/strong>Chuy\u1ec3n c\u00e1c ph\u1ea7n l\u1ecbch s\u1eed ho\u1eb7c kh\u00f4ng ho\u1ea1t \u0111\u1ed9ng c\u1ee7a c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p sang c\u00e1c b\u1ea3ng l\u01b0u tr\u1eef.<\/li>\n<li><strong>Chia t\u00e1ch:<\/strong> N\u1ebfu d\u1eef li\u1ec7u r\u1ea5t l\u1edbn, h\u00e3y chia t\u00e1ch b\u1ea3ng theo danh m\u1ee5c g\u1ed1c.<\/li>\n<\/ul>\n<h2>\ud83d\udcdd T\u00f3m t\u1eaft c\u00e1c th\u1ef1c h\u00e0nh t\u1ed1t nh\u1ea5t<\/h2>\n<p>\u0110\u1ec3 \u0111\u1ea3m b\u1ea3o tri\u1ec3n khai c\u00e1c th\u1ef1c th\u1ec3 t\u1ef1 tham chi\u1ebfu m\u1ed9t c\u00e1ch v\u1eefng ch\u1eafc, h\u00e3y tu\u00e2n theo c\u00e1c h\u01b0\u1edbng d\u1eabn sau.<\/p>\n<ul>\n<li><strong>S\u1eed d\u1ee5ng kh\u00f3a gi\u1ea3:<\/strong>\u01afu ti\u00ean s\u1eed d\u1ee5ng c\u00e1c s\u1ed1 nguy\u00ean t\u1ef1 t\u0103ng d\u1ea7n thay v\u00ec kh\u00f3a kinh doanh cho kh\u00f3a ch\u00ednh.<\/li>\n<li><strong>Cho ph\u00e9p gi\u00e1 tr\u1ecb NULL:<\/strong>\u0110\u1ea3m b\u1ea3o c\u1ed9t kh\u00f3a ngo\u1ea1i cho ph\u00e9p gi\u00e1 tr\u1ecb NULL \u0111\u1ed1i v\u1edbi c\u00e1c n\u00fat g\u1ed1c.<\/li>\n<li><strong>Ch\u1ec9 m\u1ee5c cho kh\u00f3a ngo\u1ea1i:<\/strong>Lu\u00f4n ch\u1ec9 m\u1ee5c c\u1ed9t ch\u1ee9a tham chi\u1ebfu \u0111\u1ebfn cha.<\/li>\n<li><strong>X\u00e1c th\u1ef1c chu tr\u00ecnh:<\/strong>Th\u1ef1c hi\u1ec7n ki\u1ec3m tra \u0111\u1ec3 ng\u0103n ch\u1eb7n tham chi\u1ebfu v\u00f2ng (A -&gt; B -&gt; A).<\/li>\n<li><strong>Gi\u1edbi h\u1ea1n \u0111\u1ec7 quy:<\/strong>\u0110\u1eb7t gi\u1edbi h\u1ea1n \u0111\u1ed9 s\u00e2u \u0111\u1ec7 quy trong truy v\u1ea5n \u0111\u1ec3 tr\u00e1nh tr\u00e0n ng\u0103n x\u1ebfp.<\/li>\n<li><strong>T\u00e0i li\u1ec7u v\u1ec1 l\u01b0\u1ee3c \u0111\u1ed3:<\/strong>R\u00f5 r\u00e0ng \u0111\u00e1nh d\u1ea5u c\u00e1c c\u1ed9t n\u00e0o l\u00e0 t\u1ef1 tham chi\u1ebfu trong t\u00e0i li\u1ec7u ERD c\u1ee7a b\u1ea1n.<\/li>\n<li><strong>L\u00ean k\u1ebf ho\u1ea1ch cho vi\u1ec7c x\u00f3a:<\/strong>X\u00e1c \u0111\u1ecbnh c\u00e1c quy t\u1eafc r\u00f5 r\u00e0ng cho vi\u1ec7c x\u00f3a lan truy\u1ec1n ho\u1eb7c \u0111\u1eb7t gi\u00e1 tr\u1ecb NULL khi x\u00f3a cha.<\/li>\n<li><strong>Ki\u1ec3m th\u1eed c\u00e1c c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p s\u00e2u:<\/strong>Ki\u1ec3m th\u1eed truy v\u1ea5n c\u1ee7a b\u1ea1n v\u1edbi \u00edt nh\u1ea5t 10 c\u1ea5p \u0111\u1ed9 s\u00e2u \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o hi\u1ec7u su\u1ea5t \u0111\u01b0\u1ee3c duy tr\u00ec.<\/li>\n<\/ul>\n<h2>\ud83d\udd2e Nh\u1eefng c\u00e2n nh\u1eafc trong t\u01b0\u01a1ng lai<\/h2>\n<p>C\u00f4ng ngh\u1ec7 c\u01a1 s\u1edf d\u1eef li\u1ec7u ti\u1ebfp t\u1ee5c ph\u00e1t tri\u1ec3n. Trong khi kh\u00e1i ni\u1ec7m v\u1ec1 th\u1ef1c th\u1ec3 t\u1ef1 tham chi\u1ebfu v\u1eabn kh\u00f4ng thay \u0111\u1ed5i, c\u00e1c c\u00f4ng c\u1ee5 \u0111\u1ec3 qu\u1ea3n l\u00fd n\u00f3 \u0111ang \u0111\u01b0\u1ee3c c\u1ea3i thi\u1ec7n.<\/p>\n<ul>\n<li><strong>C\u01a1 s\u1edf d\u1eef li\u1ec7u \u0111\u1ed3 th\u1ecb:<\/strong> M\u1ed9t s\u1ed1 h\u1ec7 th\u1ed1ng hi\u1ec7n \u0111\u1ea1i coi m\u1ed1i quan h\u1ec7 l\u00e0 \u0111\u1ed1i t\u01b0\u1ee3ng h\u00e0ng \u0111\u1ea7u. Ch\u00fang x\u1eed l\u00fd c\u00e1c \u0111\u01b0\u1eddng \u0111i \u0111\u1ec7 quy m\u1ed9t c\u00e1ch t\u1ef1 nhi\u00ean m\u00e0 kh\u00f4ng c\u1ea7n ph\u1ee9c t\u1ea1p SQL.<\/li>\n<li><strong>H\u1ed7 tr\u1ee3 JSON:<\/strong>C\u00e1c \u0111\u1ed9ng c\u01a1 c\u01a1 s\u1edf d\u1eef li\u1ec7u m\u1edbi cho ph\u00e9p l\u01b0u tr\u1eef d\u1eef li\u1ec7u ph\u00e2n c\u1ea5p trong c\u00e1c c\u1ed9t JSON, \u0111i\u1ec1u n\u00e0y c\u00f3 th\u1ec3 \u0111\u01a1n gi\u1ea3n h\u00f3a thi\u1ebft k\u1ebf l\u01b0\u1ee3c \u0111\u1ed3 cho c\u00e1c c\u1ea5u tr\u00fac l\u1ed3ng nhau s\u00e2u.<\/li>\n<li><strong>C\u1ea3i ti\u1ebfn ORM:<\/strong>C\u00e1c tr\u00ecnh \u00e1nh x\u1ea1 \u0111\u1ed1i t\u01b0\u1ee3ng-quan h\u1ec7 \u0111ang ng\u00e0y c\u00e0ng t\u1ed1t h\u01a1n trong vi\u1ec7c x\u1eed l\u00fd c\u00e1c m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy t\u1ef1 \u0111\u1ed9ng, gi\u1ea3m thi\u1ec3u m\u00e3 m\u1eabu.<\/li>\n<\/ul>\n<p>M\u1eb7c d\u00f9 c\u00f3 nh\u1eefng ti\u1ebfn b\u1ed9 n\u00e0y, logic c\u1ed1t l\u00f5i c\u1ee7a m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy v\u1eabn nh\u01b0 c\u0169. Hi\u1ec3u r\u00f5 c\u01a1 ch\u1ebf n\u1ec1n t\u1ea3ng c\u1ee7a kh\u00f3a ch\u00ednh, kh\u00f3a ngo\u1ea1i v\u00e0 c\u00e1c m\u1ed1i quan h\u1ec7 b\u1ea3ng l\u00e0 \u0111i\u1ec1u c\u1ea7n thi\u1ebft \u0111\u1ed1i v\u1edbi b\u1ea5t k\u1ef3 chuy\u00ean gia k\u1ef9 thu\u1eadt n\u00e0o l\u00e0m vi\u1ec7c v\u1edbi c\u1ea5u tr\u00fac d\u1eef li\u1ec7u.<\/p>\n<p>B\u1eb1ng c\u00e1ch tu\u00e2n theo c\u00e1c nguy\u00ean t\u1eafc n\u00e0y, b\u1ea1n c\u00f3 th\u1ec3 x\u00e2y d\u1ef1ng c\u00e1c h\u1ec7 th\u1ed1ng \u0111\u1ee7 linh ho\u1ea1t \u0111\u1ec3 x\u1eed l\u00fd c\u00e1c c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p ph\u1ee9c t\u1ea1p trong khi v\u1eabn \u0111\u1ea3m b\u1ea3o hi\u1ec7u su\u1ea5t v\u00e0 kh\u1ea3 n\u0103ng b\u1ea3o tr\u00ec. Th\u1ef1c th\u1ec3 t\u1ef1 tham chi\u1ebfu l\u00e0 m\u1ed9t c\u00f4ng c\u1ee5 m\u1ea1nh m\u1ebd trong b\u1ed9 c\u00f4ng c\u1ee5 m\u00f4 h\u00ecnh h\u00f3a d\u1eef li\u1ec7u c\u1ee7a b\u1ea1n, mi\u1ec5n l\u00e0 n\u00f3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng m\u1ed9t c\u00e1ch ch\u00ednh x\u00e1c v\u00e0 c\u1ea9n tr\u1ecdng.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Trong ki\u1ebfn tr\u00fac ph\u1ee9c t\u1ea1p c\u1ee7a thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u, \u00edt kh\u00e1i ni\u1ec7m n\u00e0o th\u00e1ch th\u1ee9c c\u00e1c k\u1ef9 s\u01b0 b\u1eb1ng th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n. C\u00f2n \u0111\u01b0\u1ee3c&hellip;<\/p>\n","protected":false},"author":1,"featured_media":1668,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_title":"C\u00e1c th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n trong ERD: H\u01b0\u1edbng d\u1eabn to\u00e0n di\u1ec7n \ud83d\udd17","_yoast_wpseo_metadesc":"H\u1ecdc c\u00e1ch thi\u1ebft k\u1ebf v\u00e0 tri\u1ec3n khai c\u00e1c th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n v\u00e0 c\u00e1c m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy trong ERD. Bao g\u1ed3m thi\u1ebft k\u1ebf l\u01b0\u1ee3c \u0111\u1ed3, x\u1eed l\u00fd c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p v\u00e0 c\u00e1c m\u1eb9o hi\u1ec7u su\u1ea5t.","fifu_image_url":"","fifu_image_alt":"","footnotes":""},"categories":[86],"tags":[82,85],"class_list":["post-1667","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-erd","tag-academic","tag-erd"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.1.1 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>C\u00e1c th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n trong ERD: H\u01b0\u1edbng d\u1eabn to\u00e0n di\u1ec7n \ud83d\udd17<\/title>\n<meta name=\"description\" content=\"H\u1ecdc c\u00e1ch thi\u1ebft k\u1ebf v\u00e0 tri\u1ec3n khai c\u00e1c th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n v\u00e0 c\u00e1c m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy trong ERD. Bao g\u1ed3m thi\u1ebft k\u1ebf l\u01b0\u1ee3c \u0111\u1ed3, x\u1eed l\u00fd c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p v\u00e0 c\u00e1c m\u1eb9o hi\u1ec7u su\u1ea5t.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.go-diagram.com\/vn\/self-referencing-entities-recursive-relationships-erd\/\" \/>\n<meta property=\"og:locale\" content=\"vi_VN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"C\u00e1c th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n trong ERD: H\u01b0\u1edbng d\u1eabn to\u00e0n di\u1ec7n \ud83d\udd17\" \/>\n<meta property=\"og:description\" content=\"H\u1ecdc c\u00e1ch thi\u1ebft k\u1ebf v\u00e0 tri\u1ec3n khai c\u00e1c th\u1ef1c th\u1ec3 tham chi\u1ebfu t\u1ef1 th\u00e2n v\u00e0 c\u00e1c m\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy trong ERD. 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