{"id":101430,"date":"2024-08-28T21:36:10","date_gmt":"2024-08-28T14:36:10","guid":{"rendered":"https:\/\/wiki.tino.org\/?p=101430"},"modified":"2025-06-16T16:20:15","modified_gmt":"2025-06-16T09:20:15","slug":"cach-tao-khoa-ngoai-trong-phpmyadmin","status":"publish","type":"post","link":"https:\/\/tino.vn\/blog\/cach-tao-khoa-ngoai-trong-phpmyadmin\/","title":{"rendered":"Kh\u00f3a ngo\u1ea1i l\u00e0 g\u00ec? C\u00e1ch t\u1ea1o kh\u00f3a ngo\u1ea1i trong phpMyAdmin \u0111\u01a1n gi\u1ea3n"},"content":{"rendered":"\n

Trong th\u1ebf gi\u1edbi c\u01a1 s\u1edf d\u1eef li\u1ec7u, vi\u1ec7c qu\u1ea3n l\u00fd v\u00e0 li\u00ean k\u1ebft c\u00e1c b\u1ea3ng d\u1eef li\u1ec7u m\u1ed9t c\u00e1ch hi\u1ec7u qu\u1ea3 l\u00e0 v\u00f4 c\u00f9ng quan tr\u1ecdng. Kh\u00f3a ngo\u1ea1i (Foreign Key) ch\u00ednh l\u00e0 c\u00f4ng c\u1ee5 gi\u00fap ch\u00fang ta th\u1ef1c hi\u1ec7n \u0111i\u1ec1u n\u00e0y. B\u00e0i vi\u1ebft n\u00e0y s\u1ebd gi\u00fap b\u1ea1n hi\u1ec3u r\u00f5 kh\u00e1i ni\u1ec7m kh\u00f3a ngo\u1ea1i l\u00e0 g\u00ec, c\u0169ng nh\u01b0 c\u00e1ch t\u1ea1o kh\u00f3a ngo\u1ea1i trong phpMyAdmin<\/a> \u0111\u01a1n gi\u1ea3n.<\/strong><\/p>\n\n\n\n

<\/a>T\u1ed5ng quan v\u1ec1 kh\u00f3a ngo\u1ea1i (Foreign Key) <\/strong><\/h2>\n\n\n\n

<\/a>Kh\u00f3a ngo\u1ea1i l\u00e0 g\u00ec?<\/strong><\/h3>\n\n\n\n

Kh\u00f3a ngo\u1ea1i (Foreign Key<\/strong>) l\u00e0 m\u1ed9t r\u00e0ng bu\u1ed9c (constraint) trong c\u01a1 s\u1edf d\u1eef li\u1ec7u quan h\u1ec7, d\u00f9ng \u0111\u1ec3 thi\u1ebft l\u1eadp m\u1ed1i quan h\u1ec7 gi\u1eefa hai b\u1ea3ng. C\u1ee5 th\u1ec3, \u0111\u00e2y l\u00e0 m\u1ed9t ho\u1eb7c m\u1ed9t t\u1eadp h\u1ee3p c\u00e1c c\u1ed9t trong m\u1ed9t b\u1ea3ng c\u00f3 nhi\u1ec7m v\u1ee5 tham chi\u1ebfu \u0111\u1ebfn kh\u00f3a ch\u00ednh (Primary Key) c\u1ee7a m\u1ed9t b\u1ea3ng kh\u00e1c. \u0110i\u1ec1u n\u00e0y gi\u00fap \u0111\u1ea3m b\u1ea3o r\u1eb1ng gi\u00e1 tr\u1ecb c\u1ee7a c\u1ed9t kh\u00f3a ngo\u1ea1i ph\u1ea3i t\u1ed3n t\u1ea1i trong c\u1ed9t kh\u00f3a ch\u00ednh c\u1ee7a b\u1ea3ng \u0111\u01b0\u1ee3c tham chi\u1ebfu, qua \u0111\u00f3 duy tr\u00ec t\u00ednh to\u00e0n v\u1eb9n tham chi\u1ebfu (referential integrity) trong c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/p>\n\n\n

\n
\"khoa-ngoai-la-gi\"
Kh\u00f3a ngo\u1ea1i l\u00e0 g\u00ec?<\/strong><\/figcaption><\/figure>\n<\/div>\n\n\n

\u0110\u1ec3 hi\u1ec3u r\u00f5 h\u01a1n, h\u00e3y h\u00ecnh dung m\u1ed9t v\u00ed d\u1ee5:<\/p>\n\n\n\n

Gi\u1ea3 s\u1eed ch\u00fang ta c\u00f3 hai b\u1ea3ng:<\/p>\n\n\n\n

B\u1ea3ng khach_hang: <\/strong>Ch\u1ee9a th\u00f4ng tin v\u1ec1 c\u00e1c kh\u00e1ch h\u00e0ng nh\u01b0 m\u00e3 kh\u00e1ch h\u00e0ng (l\u00e0 kh\u00f3a ch\u00ednh), t\u00ean, \u0111\u1ecba ch\u1ec9,…<\/p>\n\n\n\n

B\u1ea3ng don_hang:<\/strong> Ch\u1ee9a th\u00f4ng tin v\u1ec1 c\u00e1c \u0111\u01a1n h\u00e0ng nh\u01b0 m\u00e3 \u0111\u01a1n h\u00e0ng, ng\u00e0y \u0111\u1eb7t h\u00e0ng, m\u00e3 kh\u00e1ch h\u00e0ng (l\u00e0 kh\u00f3a ngo\u1ea1i),…<\/p>\n\n\n\n

Trong b\u1ea3ng don_hang<\/strong>, tr\u01b0\u1eddng ma_khach_hang<\/strong> ch\u00ednh l\u00e0 kh\u00f3a ngo\u1ea1i, tham chi\u1ebfu \u0111\u1ebfn tr\u01b0\u1eddng ma_khach_hang <\/strong>(kh\u00f3a ch\u00ednh) trong b\u1ea3ng khach_hang<\/strong>. \u0110i\u1ec1u n\u00e0y c\u00f3 ngh\u0129a l\u00e0:<\/p>\n\n\n\n

M\u1ed7i \u0111\u01a1n h\u00e0ng ph\u1ea3i thu\u1ed9c v\u1ec1 m\u1ed9t kh\u00e1ch h\u00e0ng duy nh\u1ea5t. Gi\u00e1 tr\u1ecb c\u1ee7a ma_khach_hang <\/strong>trong b\u1ea3ng don_hang<\/strong> ph\u1ea3i t\u1ed3n t\u1ea1i trong b\u1ea3ng khach_hang<\/strong>.<\/p>\n\n\n\n

Ch\u00fang ta c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng kh\u00f3a ngo\u1ea1i \u0111\u1ec3 li\u00ean k\u1ebft hai b\u1ea3ng l\u1ea1i v\u1edbi nhau. V\u00ed d\u1ee5, mu\u1ed1n t\u00ecm t\u1ea5t c\u1ea3 c\u00e1c \u0111\u01a1n h\u00e0ng c\u1ee7a m\u1ed9t kh\u00e1ch h\u00e0ng c\u1ee5 th\u1ec3, ch\u00fang ta ch\u1ec9 c\u1ea7n t\u00ecm ki\u1ebfm theo gi\u00e1 tr\u1ecb c\u1ee7a kh\u00f3a ngo\u1ea1i trong b\u1ea3ng don_hang<\/strong>.<\/p>\n\n\n

\n
\"khoa-ngoai-giup-duy-tri-tinh-toan-ven-tham-chieu-trong-co-so-du-lieu\"
Kh\u00f3a ngo\u1ea1i gi\u00fap duy tr\u00ec t\u00ednh to\u00e0n v\u1eb9n tham chi\u1ebfu trong c\u01a1 s\u1edf d\u1eef li\u1ec7u<\/strong><\/figcaption><\/figure>\n<\/div>\n\n\n

<\/a>T\u1ea1i sao c\u1ea7n kh\u00f3a ngo\u1ea1i khi thao t\u00e1c v\u1edbi c\u01a1 s\u1edf d\u1eef li\u1ec7u?<\/strong><\/h3>\n\n\n\n

<\/a>\u0110\u1ea3m b\u1ea3o t\u00ednh to\u00e0n v\u1eb9n tham chi\u1ebfu<\/strong><\/h4>\n\n\n\n

Kh\u00f3a ngo\u1ea1i gi\u00fap \u0111\u1ea3m b\u1ea3o r\u1eb1ng m\u1ecdi gi\u00e1 tr\u1ecb trong tr\u01b0\u1eddng kh\u00f3a ngo\u1ea1i ph\u1ea3i t\u1ed3n t\u1ea1i trong tr\u01b0\u1eddng kh\u00f3a ch\u00ednh c\u1ee7a b\u1ea3ng \u0111\u01b0\u1ee3c tham chi\u1ebfu. \u0110i\u1ec1u n\u00e0y ng\u0103n ch\u1eb7n vi\u1ec7c nh\u1eadp d\u1eef li\u1ec7u kh\u00f4ng h\u1ee3p l\u1ec7 ho\u1eb7c kh\u00f4ng t\u1ed3n t\u1ea1i, gi\u00fap duy tr\u00ec t\u00ednh nh\u1ea5t qu\u00e1n c\u1ee7a d\u1eef li\u1ec7u trong to\u00e0n b\u1ed9 h\u1ec7 th\u1ed1ng. Khi m\u1ed9t b\u1ea3n ghi trong b\u1ea3ng ch\u00ednh b\u1ecb x\u00f3a ho\u1eb7c c\u1eadp nh\u1eadt, c\u00e1c b\u1ea3n ghi li\u00ean quan trong b\u1ea3ng ph\u1ee5 c\u0169ng s\u1ebd \u0111\u01b0\u1ee3c \u0111i\u1ec1u ch\u1ec9nh t\u01b0\u01a1ng \u1ee9ng.<\/p>\n\n\n\n

<\/a>T\u1ea1o m\u1ed1i quan h\u1ec7 gi\u1eefa c\u00e1c b\u1ea3ng<\/strong><\/h4>\n\n\n\n

Kh\u00f3a ngo\u1ea1i gi\u00fap x\u00e1c \u0111\u1ecbnh m\u1ed1i quan h\u1ec7 gi\u1eefa c\u00e1c b\u1ea3ng trong c\u01a1 s\u1edf d\u1eef li\u1ec7u. V\u00ed d\u1ee5, trong m\u1ed9t h\u1ec7 th\u1ed1ng qu\u1ea3n l\u00fd \u0111\u01a1n h\u00e0ng, b\u1ea3ng “Orders”<\/strong> c\u00f3 th\u1ec3 ch\u1ee9a tr\u01b0\u1eddng kh\u00f3a ngo\u1ea1i “EmployeeID<\/strong>” \u0111\u1ec3 li\u00ean k\u1ebft v\u1edbi b\u1ea3ng “Employees<\/strong>“. \u0110i\u1ec1u n\u00e0y cho ph\u00e9p ng\u01b0\u1eddi d\u00f9ng d\u1ec5 d\u00e0ng truy xu\u1ea5t th\u00f4ng tin v\u1ec1 nh\u00e2n vi\u00ean \u0111\u00e3 x\u1eed l\u00fd \u0111\u01a1n h\u00e0ng m\u00e0 kh\u00f4ng c\u1ea7n ph\u1ea3i l\u01b0u tr\u1eef th\u00f4ng tin nh\u00e2n vi\u00ean trong b\u1ea3ng \u0111\u01a1n h\u00e0ng, t\u1eeb \u0111\u00f3 ti\u1ebft ki\u1ec7m kh\u00f4ng gian l\u01b0u tr\u1eef v\u00e0 gi\u1ea3m thi\u1ec3u s\u1ef1 tr\u00f9ng l\u1eb7p d\u1eef li\u1ec7u.<\/p>\n\n\n

\n
\"tai-sao-can-khoa-ngoai-khi-thao-tac-voi-co-so-du-lieu\"
T\u1ea1i sao c\u1ea7n kh\u00f3a ngo\u1ea1i khi thao t\u00e1c v\u1edbi c\u01a1 s\u1edf d\u1eef li\u1ec7u?<\/strong><\/figcaption><\/figure>\n<\/div>\n\n\n

<\/a>T\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n<\/strong><\/h4>\n\n\n\n

Khi c\u00e1c b\u1ea3ng \u0111\u01b0\u1ee3c li\u00ean k\u1ebft th\u00f4ng qua kh\u00f3a ngo\u1ea1i, vi\u1ec7c truy v\u1ea5n d\u1eef li\u1ec7u t\u1eeb nhi\u1ec1u b\u1ea3ng tr\u1edf n\u00ean d\u1ec5 d\u00e0ng v\u00e0 hi\u1ec7u qu\u1ea3 h\u01a1n. C\u00e1c h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng th\u00f4ng tin v\u1ec1 m\u1ed1i quan h\u1ec7 gi\u1eefa c\u00e1c b\u1ea3ng \u0111\u1ec3 t\u1ed1i \u01b0u h\u00f3a c\u00e1c truy v\u1ea5n, gi\u1ea3m thi\u1ec3u th\u1eddi gian x\u1eed l\u00fd v\u00e0 t\u0103ng c\u01b0\u1eddng hi\u1ec7u su\u1ea5t. \u0110i\u1ec1u n\u00e0y \u0111\u1eb7c bi\u1ec7t h\u1eefu \u00edch trong c\u00e1c h\u1ec7 th\u1ed1ng l\u1edbn, n\u01a1i m\u00e0 hi\u1ec7u su\u1ea5t truy v\u1ea5n l\u00e0 y\u1ebfu t\u1ed1 quan tr\u1ecdng.<\/p>\n\n\n\n

<\/a>H\u1ed7 tr\u1ee3 qu\u1ea3n l\u00fd c\u01a1 s\u1edf d\u1eef li\u1ec7u<\/strong><\/h4>\n\n\n\n

S\u1eed d\u1ee5ng kh\u00f3a ngo\u1ea1i c\u0169ng gi\u00fap qu\u1ea3n l\u00fd d\u1eef li\u1ec7u hi\u1ec7u qu\u1ea3 h\u01a1n. Khi c\u00f3 s\u1ef1 thay \u0111\u1ed5i trong m\u1ed9t b\u1ea3ng (v\u00ed d\u1ee5, x\u00f3a m\u1ed9t nh\u00e2n vi\u00ean), h\u1ec7 th\u1ed1ng c\u00f3 th\u1ec3 t\u1ef1 \u0111\u1ed9ng c\u1eadp nh\u1eadt ho\u1eb7c x\u00f3a c\u00e1c b\u1ea3n ghi li\u00ean quan trong b\u1ea3ng kh\u00e1c, nh\u1edd v\u00e0o c\u00e1c quy t\u1eafc r\u00e0ng bu\u1ed9c m\u00e0 kh\u00f3a ngo\u1ea1i thi\u1ebft l\u1eadp. \u0110i\u1ec1u n\u00e0y kh\u00f4ng ch\u1ec9 gi\u00fap duy tr\u00ec t\u00ednh nh\u1ea5t qu\u00e1n c\u1ee7a d\u1eef li\u1ec7u m\u00e0 c\u00f2n gi\u1ea3m thi\u1ec3u kh\u1ea3 n\u0103ng x\u1ea3y ra l\u1ed7i do s\u1ef1 thay \u0111\u1ed5i kh\u00f4ng \u0111\u1ed3ng b\u1ed9 gi\u1eefa c\u00e1c b\u1ea3ng.<\/p>\n\n\n\n

<\/a>T\u0103ng c\u01b0\u1eddng b\u1ea3o m\u1eadt v\u00e0 ki\u1ec3m so\u00e1t truy c\u1eadp<\/strong><\/h4>\n\n\n\n

Kh\u00f3a ngo\u1ea1i c\u0169ng \u0111\u00f3ng vai tr\u00f2 quan tr\u1ecdng trong vi\u1ec7c t\u0103ng c\u01b0\u1eddng b\u1ea3o m\u1eadt v\u00e0 ki\u1ec3m so\u00e1t truy c\u1eadp d\u1eef li\u1ec7u. B\u1eb1ng c\u00e1ch thi\u1ebft l\u1eadp c\u00e1c r\u00e0ng bu\u1ed9c kh\u00f3a ngo\u1ea1i, c\u00e1c nh\u00e0 qu\u1ea3n tr\u1ecb c\u00f3 th\u1ec3 ki\u1ec3m so\u00e1t ai c\u00f3 quy\u1ec1n truy c\u1eadp v\u00e0o d\u1eef li\u1ec7u n\u00e0o v\u00e0 \u0111\u1ea3m b\u1ea3o r\u1eb1ng ch\u1ec9 nh\u1eefng ng\u01b0\u1eddi c\u00f3 quy\u1ec1n h\u1ee3p l\u1ec7 m\u1edbi c\u00f3 th\u1ec3 th\u1ef1c hi\u1ec7n c\u00e1c thao t\u00e1c tr\u00ean d\u1eef li\u1ec7u li\u00ean quan. \u0110i\u1ec1u n\u00e0y gi\u00fap b\u1ea3o v\u1ec7 d\u1eef li\u1ec7u kh\u1ecfi nh\u1eefng thay \u0111\u1ed5i kh\u00f4ng mong mu\u1ed1n v\u00e0 \u0111\u1ea3m b\u1ea3o r\u1eb1ng ch\u1ec9 nh\u1eefng th\u00f4ng tin ch\u00ednh x\u00e1c v\u00e0 h\u1ee3p l\u1ec7 \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef trong c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/p>\n\n\n\n

<\/a>H\u01b0\u1edbng d\u1eabn c\u00e1ch t\u1ea1o kh\u00f3a ngo\u1ea1i trong phpMyAdmin<\/strong><\/h2>\n\n\n\n

B\u00e0i vi\u1ebft s\u1ebd l\u1ea5y v\u00ed d\u1ee5 v\u1ec1 c\u00e1ch t\u1ea1o kh\u00f3a ngo\u1ea1i cho b\u1ea3ng Wphe_posts<\/strong> trong database WordPress<\/a>. Trong m\u1ed9t c\u01a1 s\u1edf d\u1eef li\u1ec7u c\u1ee7a WordPress, b\u1ea3ng Wphe_posts<\/strong> th\u01b0\u1eddng l\u01b0u tr\u1eef th\u00f4ng tin v\u1ec1 c\u00e1c b\u00e0i vi\u1ebft. \u0110\u1ec3 thi\u1ebft l\u1eadp kh\u00f3a ngo\u1ea1i trong phpMyAdmin, b\u1ea1n c\u1ea7n \u0111\u1ea3m b\u1ea3o r\u1eb1ng c\u00e1c c\u1ed9t trong b\u1ea3ng c\u1ee7a b\u1ea1n c\u00f3 ki\u1ec3u d\u1eef li\u1ec7u ph\u00f9 h\u1ee3p v\u00e0 c\u00f3 li\u00ean k\u1ebft v\u1edbi c\u1ed9t c\u1ee7a b\u1ea3ng kh\u00e1c. D\u01b0\u1edbi \u0111\u00e2y l\u00e0 h\u01b0\u1edbng d\u1eabn chi ti\u1ebft:<\/p>\n\n\n\n

B\u01b0\u1edbc 1: Truy c\u1eadp phpMyAdmin v\u00e0 ch\u1ecdn c\u01a1 s\u1edf d\u1eef li\u1ec7u<\/strong><\/h3>\n\n\n\n

\u0110\u0103ng nh\u1eadp v\u00e0o phpMyAdmin. Trong danh s\u00e1ch c\u00e1c c\u01a1 s\u1edf d\u1eef li\u1ec7u \u1edf c\u1ed9t b\u00ean tr\u00e1i, ch\u1ecdn c\u01a1 s\u1edf d\u1eef li\u1ec7u m\u00e0 b\u1ea1n mu\u1ed1n t\u1ea1o kh\u00f3a ngo\u1ea1i.<\/p>\n\n\n\n

B\u01b0\u1edbc 2: X\u00e1c \u0111\u1ecbnh b\u1ea3ng v\u00e0 c\u1ed9t c\u1ea7n thi\u1ebft l\u1eadp kh\u00f3a ngo\u1ea1i<\/strong><\/h3>\n\n\n\n

Gi\u1ea3 s\u1eed b\u1ea1n mu\u1ed1n thi\u1ebft l\u1eadp m\u1ed9t kh\u00f3a ngo\u1ea1i cho c\u1ed9t post_author <\/strong>trong b\u1ea3ng Wphe_posts<\/strong>, li\u00ean k\u1ebft v\u1edbi c\u1ed9t ID trong b\u1ea3ng Wphe_users<\/strong> (b\u1ea3ng l\u01b0u tr\u1eef th\u00f4ng tin ng\u01b0\u1eddi d\u00f9ng).<\/p>\n\n\n\n