{"id":1631,"date":"2026-04-08T07:46:40","date_gmt":"2026-04-08T07:46:40","guid":{"rendered":"https:\/\/www.viz-note.com\/vi\/erd-elements-confusion-breakdown\/"},"modified":"2026-04-08T07:46:40","modified_gmt":"2026-04-08T07:46:40","slug":"erd-elements-confusion-breakdown","status":"publish","type":"post","link":"https:\/\/www.viz-note.com\/vi\/erd-elements-confusion-breakdown\/","title":{"rendered":"Ph\u00e2n t\u00edch chi ti\u1ebft c\u00e1c th\u00e0nh ph\u1ea7n c\u1ee7a s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 g\u00e2y nh\u1ea7m l\u1eabn ph\u1ed5 bi\u1ebfn nh\u1ea5t"},"content":{"rendered":"

Thi\u1ebft k\u1ebf m\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 c\u01a1 s\u1edf d\u1eef li\u1ec7u v\u1eefng ch\u1eafc \u0111\u00f2i h\u1ecfi s\u1ef1 ch\u00ednh x\u00e1c. S\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 (ERD) \u0111\u00f3ng vai tr\u00f2 nh\u01b0 b\u1ea3n v\u1ebd thi\u1ebft k\u1ebf cho c\u1ea5u tr\u00fac n\u00e0y, chuy\u1ec3n \u0111\u1ed5i logic kinh doanh ph\u1ee9c t\u1ea1p th\u00e0nh \u0111\u1ecbnh d\u1ea1ng tr\u1ef1c quan m\u00e0 c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n v\u00e0 b\u00ean li\u00ean quan c\u00f3 th\u1ec3 hi\u1ec3u \u0111\u01b0\u1ee3c. Tuy nhi\u00ean, d\u00f9 mang l\u1ea1i nhi\u1ec1u l\u1ee3i \u00edch, ERD th\u01b0\u1eddng tr\u1edf th\u00e0nh ngu\u1ed3n g\u00e2y hi\u1ec3u l\u1ea7m trong giai \u0111o\u1ea1n m\u00f4 h\u00ecnh h\u00f3a. S\u1ef1 m\u01a1 h\u1ed3 trong k\u00fd hi\u1ec7u, hi\u1ec3u sai v\u1ec1 t\u00ednh cardinality v\u00e0 nh\u1ea7m l\u1eabn v\u1ec1 lo\u1ea1i thu\u1ed9c t\u00ednh c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn c\u00f4ng vi\u1ec7c s\u1eeda \u0111\u1ed5i l\u1edbn trong giai \u0111o\u1ea1n ph\u00e1t tri\u1ec3n sau n\u00e0y.<\/p>\n

H\u01b0\u1edbng d\u1eabn n\u00e0y cung c\u1ea5p ph\u00e2n t\u00edch chi ti\u1ebft v\u1ec1 c\u00e1c th\u00e0nh ph\u1ea7n c\u1ee5 th\u1ec3 trong ERD th\u01b0\u1eddng g\u00e2y kh\u00f3 kh\u0103n cho c\u00e1c ki\u1ebfn tr\u00fac s\u01b0 c\u01a1 s\u1edf d\u1eef li\u1ec7u v\u00e0 k\u1ef9 s\u01b0. B\u1eb1ng c\u00e1ch l\u00e0m r\u00f5 s\u1ef1 kh\u00e1c bi\u1ec7t gi\u1eefa c\u00e1c th\u1ef1c th\u1ec3 m\u1ea1nh v\u00e0 y\u1ebfu, ph\u00e2n t\u00edch k\u00fd hi\u1ec7u m\u1ed1i quan h\u1ec7 v\u00e0 ph\u00e2n lo\u1ea1i thu\u1ed9c t\u00ednh, ch\u00fang ta c\u00f3 th\u1ec3 gi\u1ea3m thi\u1ec3u sai s\u00f3t v\u00e0 \u0111\u1ea3m b\u1ea3o m\u00f4 h\u00ecnh d\u1eef li\u1ec7u cu\u1ed1i c\u00f9ng ph\u1ea3n \u00e1nh ch\u00ednh x\u00e1c c\u00e1c y\u00eau c\u1ea7u v\u1eadn h\u00e0nh.<\/p>\n

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\"Cartoon<\/figure>\n<\/div>\n

\ud83c\udfd7\ufe0f Ki\u1ec3u th\u1ef1c th\u1ec3: Ph\u00e2n bi\u1ec7t th\u1ef1c th\u1ec3 m\u1ea1nh v\u00e0 y\u1ebfu<\/h2>\n

\u1ede trung t\u00e2m c\u1ee7a b\u1ea5t k\u1ef3 ERD n\u00e0o l\u00e0 c\u00e1c th\u1ef1c th\u1ec3. Ch\u00fang \u0111\u1ea1i di\u1ec7n cho c\u00e1c \u0111\u1ed1i t\u01b0\u1ee3ng ho\u1eb7c kh\u00e1i ni\u1ec7m m\u00e0 d\u1eef li\u1ec7u \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef. Trong khi ph\u1ea7n l\u1edbn c\u00e1c chuy\u00ean gia \u0111\u1ec1u hi\u1ec3u kh\u00e1i ni\u1ec7m v\u1ec1 b\u1ea3ng, th\u00ec s\u1ef1 ph\u00e2n bi\u1ec7t gi\u1eefa th\u1ef1c th\u1ec3 m\u1ea1nh v\u00e0 y\u1ebfu ch\u00ednh l\u00e0 n\u01a1i th\u01b0\u1eddng x\u1ea3y ra \u0111i\u1ec3m nh\u1ea7m l\u1eabn l\u1edbn \u0111\u1ea7u ti\u00ean.<\/p>\n

    \n
  • Th\u1ef1c th\u1ec3 m\u1ea1nh:<\/strong> Nh\u1eefng th\u1ef1c th\u1ec3 n\u00e0y s\u1edf h\u1eefu kh\u00f3a ch\u00ednh ri\u00eang c\u1ee7a ch\u00fang. Ch\u00fang \u0111\u1ed9c l\u1eadp v\u00e0 kh\u00f4ng ph\u1ee5 thu\u1ed9c v\u00e0o c\u00e1c th\u1ef1c th\u1ec3 kh\u00e1c \u0111\u1ec3 x\u00e1c \u0111\u1ecbnh. V\u00ed d\u1ee5, m\u1ed9t Kh\u00e1ch h\u00e0ng<\/code>th\u1ef1c th\u1ec3 th\u01b0\u1eddng c\u00f3 ID Kh\u00e1ch h\u00e0ng duy nh\u1ea5t, khi\u1ebfn n\u00f3 tr\u1edf th\u00e0nh th\u1ef1c th\u1ec3 m\u1ea1nh.<\/li>\n
  • Th\u1ef1c th\u1ec3 y\u1ebfu:<\/strong> Nh\u1eefng th\u1ef1c th\u1ec3 n\u00e0y kh\u00f4ng th\u1ec3 \u0111\u01b0\u1ee3c x\u00e1c \u0111\u1ecbnh duy nh\u1ea5t ch\u1ec9 b\u1eb1ng c\u00e1c thu\u1ed9c t\u00ednh ri\u00eang c\u1ee7a ch\u00fang. Ch\u00fang ph\u1ee5 thu\u1ed9c v\u00e0o m\u1ed1i quan h\u1ec7 v\u1edbi m\u1ed9t th\u1ef1c th\u1ec3 kh\u00e1c, \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 cha x\u00e1c \u0111\u1ecbnh, \u0111\u1ec3 t\u1ed3n t\u1ea1i. M\u1ed9t D\u00f2ng h\u00e0ng<\/code> trong h\u1ec7 th\u1ed1ng \u0111\u01a1n h\u00e0ng c\u00f3 th\u1ec3 ch\u1ec9 t\u1ed3n t\u1ea1i trong b\u1ed1i c\u1ea3nh c\u1ee7a m\u1ed9t \u0110\u01a1n h\u00e0ng<\/code>.<\/li>\n<\/ul>\n

    S\u1ef1 nh\u1ea7m l\u1eabn th\u01b0\u1eddng xu\u1ea5t ph\u00e1t t\u1eeb c\u00e1ch ch\u00fang \u0111\u01b0\u1ee3c bi\u1ec3u di\u1ec5n tr\u1ef1c quan. M\u1ed9t th\u1ef1c th\u1ec3 m\u1ea1nh th\u01b0\u1eddng \u0111\u01b0\u1ee3c v\u1ebd b\u1eb1ng h\u00ecnh ch\u1eef nh\u1eadt th\u00f4ng th\u01b0\u1eddng. M\u1ed9t th\u1ef1c th\u1ec3 y\u1ebfu th\u01b0\u1eddng \u0111\u01b0\u1ee3c th\u1ec3 hi\u1ec7n b\u1eb1ng h\u00ecnh ch\u1eef nh\u1eadt k\u00e9p. Vi\u1ec7c kh\u00f4ng ph\u00e2n bi\u1ec7t r\u00f5 r\u00e0ng \u0111i\u1ec1u n\u00e0y v\u1ec1 m\u1eb7t tr\u1ef1c quan c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn l\u1ed7i tri\u1ec3n khai c\u01a1 s\u1edf d\u1eef li\u1ec7u, khi b\u1ea3ng th\u1ef1c th\u1ec3 y\u1ebfu \u0111\u01b0\u1ee3c t\u1ea1o ra m\u00e0 kh\u00f4ng c\u00f3 c\u00e1c r\u00e0ng bu\u1ed9c kh\u00f3a ngo\u1ea1i c\u1ea7n thi\u1ebft \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o m\u1ed1i ph\u1ee5 thu\u1ed9c c\u1ee7a n\u00f3.<\/p>\n

    H\u1ec7 qu\u1ea3 c\u1ee7a vi\u1ec7c ph\u00e2n lo\u1ea1i sai<\/h3>\n

    Khi m\u1ed9t th\u1ef1c th\u1ec3 y\u1ebfu \u0111\u01b0\u1ee3c m\u00f4 h\u00ecnh h\u00f3a nh\u01b0 th\u1ef1c th\u1ec3 m\u1ea1nh, c\u01a1 s\u1edf d\u1eef li\u1ec7u c\u00f3 th\u1ec3 cho ph\u00e9p c\u00e1c b\u1ea3n ghi t\u1ed3n t\u1ea1i m\u00e0 kh\u00f4ng c\u00f3 cha. \u0110i\u1ec1u n\u00e0y t\u1ea1o ra d\u1eef li\u1ec7u b\u1ecb b\u1ecf r\u01a1i. Ng\u01b0\u1ee3c l\u1ea1i, m\u00f4 h\u00ecnh h\u00f3a m\u1ed9t th\u1ef1c th\u1ec3 m\u1ea1nh th\u00e0nh th\u1ef1c th\u1ec3 y\u1ebfu s\u1ebd bu\u1ed9c ph\u1ea3i ph\u1ee5 thu\u1ed9c kh\u00f4ng c\u1ea7n thi\u1ebft, c\u00f3 th\u1ec3 l\u00e0m h\u1ea1n ch\u1ebf kh\u1ea3 n\u0103ng s\u1eed d\u1ee5ng c\u1ee7a th\u1ef1c th\u1ec3 b\u00ean ngo\u00e0i b\u1ed1i c\u1ea3nh ch\u00ednh c\u1ee7a n\u00f3. R\u1ea5t quan tr\u1ecdng l\u00e0 ph\u1ea3i x\u00e1c \u0111\u1ecbnh xem m\u1ed9t \u0111\u1ed1i t\u01b0\u1ee3ng c\u00f3 th\u1ec3 t\u1ed3n t\u1ea1i \u0111\u1ed9c l\u1eadp hay kh\u00f4ng tr\u01b0\u1edbc khi g\u00e1n cho n\u00f3 tr\u1ea1ng th\u00e1i th\u1ef1c th\u1ec3 m\u1ea1nh.<\/p>\n

      \n
    • Ki\u1ec3m tra t\u00ednh \u0111\u1ed9c l\u1eadp:<\/strong> B\u1ea3n ghi n\u00e0y c\u00f3 th\u1ec3 t\u1ed3n t\u1ea1i m\u00e0 kh\u00f4ng c\u1ea7n li\u00ean k\u1ebft v\u1edbi b\u1ea3n ghi kh\u00e1c kh\u00f4ng?<\/li>\n
    • Ngu\u1ed3n \u0111\u1ecbnh danh:<\/strong> ID duy nh\u1ea5t \u0111\u1ebfn t\u1eeb th\u1ef1c th\u1ec3 \u0111\u00f3 hay t\u1eeb m\u1ed1i quan h\u1ec7?<\/li>\n
    • Ph\u1ee5 thu\u1ed9c v\u00e0o s\u1ef1 t\u1ed3n t\u1ea1i:<\/strong> Vi\u1ec7c x\u00f3a cha c\u00f3 t\u1ef1 \u0111\u1ed9ng x\u00f3a con kh\u00f4ng?<\/li>\n<\/ul>\n

      \ud83d\udd17 Cardinality v\u00e0 t\u00ednh t\u00f9y ch\u1ecdn c\u1ee7a m\u1ed1i quan h\u1ec7<\/h2>\n

      C\u00e1c m\u1ed1i quan h\u1ec7 x\u00e1c \u0111\u1ecbnh c\u00e1ch c\u00e1c th\u1ef1c th\u1ec3 t\u01b0\u01a1ng t\u00e1c v\u1edbi nhau. Cardinality x\u00e1c \u0111\u1ecbnh s\u1ed1 l\u01b0\u1ee3ng b\u1ea3n ghi c\u1ee7a m\u1ed9t th\u1ef1c th\u1ec3 c\u00f3 th\u1ec3 ho\u1eb7c ph\u1ea3i li\u00ean k\u1ebft v\u1edbi m\u1ed7i b\u1ea3n ghi c\u1ee7a th\u1ef1c th\u1ec3 kh\u00e1c. \u0110\u00e2y c\u00f3 l\u1ebd l\u00e0 khu v\u1ef1c g\u00e2y nh\u1ea7m l\u1eabn ph\u1ed5 bi\u1ebfn nh\u1ea5t do s\u1ef1 kh\u00e1c bi\u1ec7t trong phong c\u00e1ch k\u00fd hi\u1ec7u.<\/p>\n

      C\u00e1c k\u00fd hi\u1ec7u cardinality<\/h3>\n

      C\u00f3 nhi\u1ec1u c\u00e1ch kh\u00e1c nhau \u0111\u1ec3 bi\u1ec3u di\u1ec5n cardinality tr\u00ean s\u01a1 \u0111\u1ed3. M\u1ed9t s\u1ed1 d\u00f9ng nh\u00e3n v\u0103n b\u1ea3n nh\u01b0 ‘1’ ho\u1eb7c ‘N’, trong khi nh\u1eefng ng\u01b0\u1eddi kh\u00e1c d\u00f9ng k\u00fd hi\u1ec7u ch\u00e2n chim. Vi\u1ec7c tr\u1ed9n l\u1eabn c\u00e1c phong c\u00e1ch n\u00e0y ho\u1eb7c hi\u1ec3u sai k\u00fd hi\u1ec7u s\u1ebd d\u1eabn \u0111\u1ebfn kho\u1ea3ng tr\u1ed1ng logic trong l\u01b0\u1ee3c \u0111\u1ed3 v\u1eadt l\u00fd.<\/p>\n\n\n\n\n\n\n\n
      K\u00fd hi\u1ec7u \/ Nh\u00e3n<\/th>\n\u00dd ngh\u0129a<\/th>\nB\u1ed1i c\u1ea3nh v\u00ed d\u1ee5<\/th>\n<\/tr>\n
      1<\/td>\nCh\u00ednh x\u00e1c m\u1ed9t<\/td>\nM\u1ed9t ng\u01b0\u1eddi c\u00f3 \u0111\u00fang m\u1ed9t s\u1ed1 b\u1ea3o hi\u1ec3m x\u00e3 h\u1ed9i.<\/td>\n<\/tr>\n
      0..1<\/td>\nKh\u00f4ng ho\u1eb7c m\u1ed9t<\/td>\nM\u1ed9t ng\u01b0\u1eddi c\u00f3 th\u1ec3 kh\u00f4ng c\u00f3 t\u00ean \u0111\u1ec7m ho\u1eb7c c\u00f3 \u0111\u00fang m\u1ed9t t\u00ean \u0111\u1ec7m.<\/td>\n<\/tr>\n
      1..1<\/td>\nCh\u1ec9 m\u1ed9t duy nh\u1ea5t<\/td>\nM\u1ed9t d\u1ef1 \u00e1n ph\u1ea3i c\u00f3 \u0111\u00fang m\u1ed9t ng\u01b0\u1eddi qu\u1ea3n l\u00fd d\u1ef1 \u00e1n \u0111\u01b0\u1ee3c giao nhi\u1ec7m v\u1ee5.<\/td>\n<\/tr>\n
      0..N<\/td>\nKh\u00f4ng \u0111\u1ebfn nhi\u1ec1u<\/td>\nM\u1ed9t \u0111\u01a1n \u0111\u1eb7t h\u00e0ng c\u00f3 th\u1ec3 c\u00f3 kh\u00f4ng c\u00f3 ho\u1eb7c nhi\u1ec1u m\u1ee5c chi ti\u1ebft.<\/td>\n<\/tr>\n
      1..N<\/td>\nM\u1ed9t \u0111\u1ebfn nhi\u1ec1u<\/td>\nM\u1ed9t ph\u00f2ng ban ph\u1ea3i c\u00f3 \u00edt nh\u1ea5t m\u1ed9t nh\u00e2n vi\u00ean ho\u1eb7c nhi\u1ec1u h\u01a1n.<\/td>\n<\/tr>\n<\/table>\n

      T\u00ednh t\u00f9y ch\u1ecdn v\u00e0 kh\u1ea3 n\u0103ng r\u1ed7ng<\/h3>\n

      T\u00ednh t\u00f9y ch\u1ecdn \u0111\u1ec1 c\u1eadp \u0111\u1ebfn vi\u1ec7c m\u1ed9t m\u1ed1i quan h\u1ec7 l\u00e0 b\u1eaft bu\u1ed9c hay t\u00f9y ch\u1ecdn. \u0110i\u1ec1u n\u00e0y \u1ea3nh h\u01b0\u1edfng tr\u1ef1c ti\u1ebfp \u0111\u1ebfn \u0111\u1ecbnh ngh\u0129a kh\u00f3a ngo\u1ea1i trong b\u1ea3ng c\u01a1 s\u1edf d\u1eef li\u1ec7u. N\u1ebfu m\u1ed1i quan h\u1ec7 l\u00e0 b\u1eaft bu\u1ed9c, c\u1ed9t kh\u00f3a ngo\u1ea1i kh\u00f4ng \u0111\u01b0\u1ee3c ph\u00e9p r\u1ed7ng. N\u1ebfu l\u00e0 t\u00f9y ch\u1ecdn, c\u1ed9t \u0111\u00f3 c\u00f3 th\u1ec3 r\u1ed7ng.<\/p>\n

      S\u1ef1 nh\u1ea7m l\u1eabn th\u01b0\u1eddng x\u1ea3y ra khi s\u01a1 \u0111\u1ed3 th\u1ec3 hi\u1ec7n \u0111\u01b0\u1eddng li\u1ec1n so v\u1edbi \u0111\u01b0\u1eddng n\u00e9t \u0111\u1ee9t. Kh\u00f4ng c\u00f3 ch\u00fa th\u00edch r\u00f5 r\u00e0ng, c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n c\u00f3 th\u1ec3 nh\u1ea7m t\u01b0\u1edfng m\u1ed1i quan h\u1ec7 b\u1eaft bu\u1ed9c trong khi th\u1ef1c t\u1ebf kh\u00f4ng t\u1ed3n t\u1ea1i, d\u1eabn \u0111\u1ebfn vi ph\u1ea1m r\u00e0ng bu\u1ed9c khi nh\u1eadp d\u1eef li\u1ec7u. R\u1ea5t quan tr\u1ecdng l\u00e0 ph\u1ea3i ghi ch\u00fa r\u00f5 ngh\u0129a c\u1ee7a c\u00e1c ki\u1ec3u \u0111\u01b0\u1eddng n\u00e9t trong t\u00e0i li\u1ec7u m\u00f4 h\u00ecnh.<\/p>\n

        \n
      • M\u1ed1i quan h\u1ec7 b\u1eaft bu\u1ed9c:<\/strong> B\u1ea3n ghi con ph\u1ea3i t\u1ed3n t\u1ea1i \u0111\u1ec3 b\u1ea3n ghi cha \u0111\u01b0\u1ee3c coi l\u00e0 h\u1ee3p l\u1ec7.<\/li>\n
      • M\u1ed1i quan h\u1ec7 t\u00f9y ch\u1ecdn:<\/strong> B\u1ea3n ghi con c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c t\u1ea1o m\u00e0 kh\u00f4ng c\u1ea7n b\u1ea3n ghi cha, ho\u1eb7c b\u1ea3n ghi cha c\u00f3 th\u1ec3 t\u1ed3n t\u1ea1i m\u00e0 kh\u00f4ng c\u1ea7n b\u1ea3n ghi con.<\/li>\n
      • R\u00e0ng bu\u1ed9c kh\u00f3a ngo\u1ea1i:<\/strong> Ph\u1ea3i \u0111\u01b0\u1ee3c thi\u1ebft l\u1eadp th\u00e0nh KH\u00d4NG R\u1ed6NG<\/code> cho b\u1eaft bu\u1ed9c, R\u1ed6NG<\/code> \u0111\u01b0\u1ee3c ph\u00e9p cho t\u00f9y ch\u1ecdn.<\/li>\n<\/ul>\n

        \ud83d\udd11 Thu\u1ed9c t\u00ednh v\u00e0 nh\u1eadn di\u1ec7n kh\u00f3a<\/h2>\n

        Thu\u1ed9c t\u00ednh l\u00e0 c\u00e1c \u0111\u1eb7c \u0111i\u1ec3m c\u1ee7a m\u1ed9t th\u1ef1c th\u1ec3. M\u1eb7c d\u00f9 c\u00f3 v\u1ebb \u0111\u01a1n gi\u1ea3n, nh\u01b0ng vi\u1ec7c ph\u00e2n lo\u1ea1i thu\u1ed9c t\u00ednh th\u00e0nh kh\u00f3a ch\u00ednh, kh\u00f3a ngo\u1ea1i v\u00e0 thu\u1ed9c t\u00ednh \u0111\u01a1n gi\u1ea3n th\u01b0\u1eddng g\u00e2y ra l\u1ed7i ph\u1ed5 bi\u1ebfn trong chu\u1ea9n h\u00f3a v\u00e0 hi\u1ec7u su\u1ea5t truy v\u1ea5n.<\/p>\n

        Kh\u00f3a ch\u00ednh so v\u1edbi kh\u00f3a ngo\u1ea1i<\/h3>\n

        Kh\u00f3a ch\u00ednh (PK) x\u00e1c \u0111\u1ecbnh duy nh\u1ea5t m\u1ed9t h\u00e0ng. Kh\u00f3a ngo\u1ea1i (FK) li\u00ean k\u1ebft m\u1ed9t h\u00e0ng v\u1edbi b\u1ea3ng cha. S\u1ef1 nh\u1ea7m l\u1eabn x\u1ea3y ra khi s\u1eed d\u1ee5ng kh\u00f3a t\u1ef1 nhi\u00ean thay v\u00ec kh\u00f3a gi\u1ea3 t\u1ea1o, ho\u1eb7c khi kh\u00f3a ch\u00ednh kh\u00f4ng \u0111\u01b0\u1ee3c \u0111\u1ecbnh ngh\u0129a nh\u1ea5t qu\u00e1n tr\u00ean to\u00e0n s\u01a1 \u0111\u1ed3.<\/p>\n

          \n
        • Kh\u00f3a t\u1ef1 nhi\u00ean:<\/strong>M\u1ed9t kh\u00f3a t\u1ed3n t\u1ea1i t\u1ef1 nhi\u00ean trong d\u1eef li\u1ec7u, v\u00ed d\u1ee5 nh\u01b0 S\u1ed1 B\u1ea3o hi\u1ec3m X\u00e3 h\u1ed9i ho\u1eb7c \u0110\u1ecba ch\u1ec9 Email. Nh\u1eefng kh\u00f3a n\u00e0y c\u00f3 th\u1ec3 thay \u0111\u1ed5i, d\u1eabn \u0111\u1ebfn c\u00e1c v\u1ea5n \u0111\u1ec1 v\u1ec1 t\u00ednh to\u00e0n v\u1eb9n.<\/li>\n
        • Kh\u00f3a gi\u1ea3 t\u1ea1o:<\/strong>M\u1ed9t kh\u00f3a nh\u00e2n t\u1ea1o \u0111\u01b0\u1ee3c h\u1ec7 th\u1ed1ng t\u1ea1o ra, v\u00ed d\u1ee5 nh\u01b0 m\u1ed9t s\u1ed1 nguy\u00ean t\u1ef1 t\u0103ng d\u1ea7n. Nh\u1eefng kh\u00f3a n\u00e0y th\u01b0\u1eddng \u0111\u01b0\u1ee3c \u01b0u ti\u00ean v\u00ec t\u00ednh \u1ed5n \u0111\u1ecbnh.<\/li>\n<\/ul>\n

          Kh\u00f3a k\u1ebft h\u1ee3p<\/h3>\n

          Kh\u00f3a k\u1ebft h\u1ee3p bao g\u1ed3m hai ho\u1eb7c nhi\u1ec1u c\u1ed9t, khi k\u1ebft h\u1ee3p l\u1ea1i s\u1ebd x\u00e1c \u0111\u1ecbnh duy nh\u1ea5t m\u1ed9t b\u1ea3n ghi. \u0110i\u1ec1u n\u00e0y ph\u1ed5 bi\u1ebfn trong c\u00e1c b\u1ea3ng li\u00ean k\u1ebft d\u00f9ng \u0111\u1ec3 gi\u1ea3i quy\u1ebft m\u1ed1i quan h\u1ec7 nhi\u1ec1u-\u0111a. S\u1ef1 nh\u1ea7m l\u1eabn \u1edf \u0111\u00e2y n\u1eb1m \u1edf th\u1ee9 t\u1ef1 c\u00e1c c\u1ed9t v\u00e0 b\u1ea3ng n\u00e0o gi\u1eef kh\u00f3a.<\/p>\n

          N\u1ebfu th\u1ee9 t\u1ef1 c\u00e1c c\u1ed9t trong kh\u00f3a k\u1ebft h\u1ee3p kh\u00f4ng \u0111\u01b0\u1ee3c duy tr\u00ec nh\u1ea5t qu\u00e1n gi\u1eefa c\u00e1c b\u1ea3ng li\u00ean quan, c\u00e1c ph\u00e9p n\u1ed1i (join) s\u1ebd th\u1ea5t b\u1ea1i ho\u1eb7c y\u00eau c\u1ea7u chuy\u1ec3n \u0111\u1ed5i ph\u1ee9c t\u1ea1p. Vi\u1ec7c ghi ch\u00fa ch\u00ednh x\u00e1c th\u1ee9 t\u1ef1 c\u1ed9t trong \u0111\u1ecbnh ngh\u0129a kh\u00f3a ch\u00ednh l\u00e0 r\u1ea5t quan tr\u1ecdng.<\/p>\n

          \ud83d\udd01 M\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy<\/h2>\n

          M\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy x\u1ea3y ra khi m\u1ed9t th\u1ef1c th\u1ec3 li\u00ean k\u1ebft v\u1edbi ch\u00ednh n\u00f3. \u0110i\u1ec1u n\u00e0y th\u01b0\u1eddng \u0111\u01b0\u1ee3c d\u00f9ng cho c\u00e1c c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p nh\u01b0 s\u01a1 \u0111\u1ed3 t\u1ed5 ch\u1ee9c ho\u1eb7c danh m\u1ee5c v\u1eadt li\u1ec7u. S\u1ef1 nh\u1ea7m l\u1eabn xu\u1ea5t ph\u00e1t t\u1eeb c\u00e1ch bi\u1ec3u di\u1ec5n tr\u1ef1c quan, v\u00ec \u0111\u01b0\u1eddng n\u1ed1i k\u1ebft n\u1ed1i th\u1ef1c th\u1ec3 v\u1edbi ch\u00ednh n\u00f3.<\/p>\n

          Kh\u00f4ng c\u00f3 nh\u00e3n r\u00f5 r\u00e0ng, th\u01b0\u1eddng kh\u00f3 x\u00e1c \u0111\u1ecbnh b\u00ean n\u00e0o trong m\u1ed1i quan h\u1ec7 \u0111\u1ea1i di\u1ec7n cho cha v\u00e0 b\u00ean n\u00e0o \u0111\u1ea1i di\u1ec7n cho con. V\u00ed d\u1ee5, trong b\u1ea3ng Nh\u00e2n vi\u00ean, m\u1ed9t nh\u00e2n vi\u00ean qu\u1ea3n l\u00fd m\u1ed9t nh\u00e2n vi\u00ean kh\u00e1c. M\u1ed1i quan h\u1ec7 ph\u1ea3i \u0111\u01b0\u1ee3c n\u00eau r\u00f5 r\u00e0ng r\u1eb1ng m\u1ed9t Nh\u00e2n vi\u00ean c\u00f3 th\u1ec3 l\u00e0 Qu\u1ea3n l\u00fd c\u1ee7a c\u00e1c Nh\u00e2n vi\u00ean kh\u00e1c.<\/p>\n

            \n
          • Tham chi\u1ebfu t\u1ef1 th\u00e2n:<\/strong>Kh\u00f3a ngo\u1ea1i trong b\u1ea3ng tr\u1ecf ng\u01b0\u1ee3c l\u1ea1i kh\u00f3a ch\u00ednh c\u1ee7a ch\u00ednh b\u1ea3ng \u0111\u00f3.<\/li>\n
          • X\u1eed l\u00fd gi\u00e1 tr\u1ecb r\u1ed7ng:<\/strong>C\u00e1c n\u00fat g\u1ed1c c\u1ee7a c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p th\u01b0\u1eddng c\u00f3 gi\u00e1 tr\u1ecb r\u1ed7ng trong c\u1ed9t ID qu\u1ea3n l\u00fd.<\/li>\n
          • H\u1ea1n ch\u1ebf v\u1ec1 \u0111\u1ed9 s\u00e2u:<\/strong>C\u00e1c truy v\u1ea5n \u0111\u1ec7 quy c\u00f3 th\u1ec3 tr\u1edf th\u00e0nh \u0111i\u1ec3m ngh\u1ebdn hi\u1ec7u su\u1ea5t n\u1ebfu c\u1ea5u tr\u00fac ph\u00e2n c\u1ea5p qu\u00e1 s\u00e2u.<\/li>\n<\/ul>\n

            \u26a0\ufe0f Nh\u1eefng sai l\u1ea7m ph\u1ed5 bi\u1ebfn trong m\u00f4 h\u00ecnh h\u00f3a<\/h2>\n

            Ngo\u00e0i c\u00e1c y\u1ebfu t\u1ed1 c\u1ee5 th\u1ec3, m\u1ed9t s\u1ed1 m\u1eabu c\u1ea5u tr\u00fac th\u01b0\u1eddng d\u1eabn \u0111\u1ebfn s\u1ef1 nh\u1ea7m l\u1eabn trong qu\u00e1 tr\u00ecnh tri\u1ec3n khai. Nh\u1eadn di\u1ec7n nh\u1eefng sai l\u1ea7m n\u00e0y s\u1edbm s\u1ebd gi\u00fap tr\u00e1nh \u0111\u01b0\u1ee3c c\u00e1c thao t\u00e1c di chuy\u1ec3n l\u01b0\u1ee3c \u0111\u1ed3 t\u1ed1n k\u00e9m.<\/p>\n

            1. Chu\u1ea9n h\u00f3a qu\u00e1 m\u1ee9c<\/h3>\n

            M\u1eb7c d\u00f9 chu\u1ea9n h\u00f3a gi\u00fap gi\u1ea3m s\u1ef1 tr\u00f9ng l\u1eb7p, nh\u01b0ng chu\u1ea9n h\u00f3a qu\u00e1 m\u1ee9c c\u00f3 th\u1ec3 khi\u1ebfn c\u00e1c truy v\u1ea5n tr\u1edf n\u00ean kh\u00f3 \u0111\u1ecdc v\u00e0 th\u1ef1c thi. T\u1ea1o m\u1ed9t b\u1ea3ng ri\u00eang bi\u1ec7t cho t\u1eebng thu\u1ed9c t\u00ednh c\u00f3 th\u1ec3 l\u00e0m ph\u00e2n m\u1ea3nh d\u1eef li\u1ec7u m\u1ed9t c\u00e1ch kh\u00f4ng c\u1ea7n thi\u1ebft. Vi\u1ec7c c\u00e2n b\u1eb1ng gi\u1eefa d\u1ea1ng chu\u1ea9n h\u00f3a th\u1ee9 ba (3NF) v\u1edbi hi\u1ec7u su\u1ea5t truy v\u1ea5n th\u1ef1c t\u1ebf l\u00e0 r\u1ea5t quan tr\u1ecdng.<\/p>\n

            2. M\u1ed1i quan h\u1ec7 nhi\u1ec1u-\u0111a m\u00e0 kh\u00f4ng c\u00f3 b\u1ea3ng li\u00ean k\u1ebft<\/h3>\n

            Trong c\u01a1 s\u1edf d\u1eef li\u1ec7u v\u1eadt l\u00fd, m\u1ed1i quan h\u1ec7 nhi\u1ec1u-\u0111a kh\u00f4ng th\u1ec3 t\u1ed3n t\u1ea1i tr\u1ef1c ti\u1ebfp. N\u00f3 ph\u1ea3i \u0111\u01b0\u1ee3c gi\u1ea3i quy\u1ebft th\u00e0nh hai m\u1ed1i quan h\u1ec7 m\u1ed9t-\u0111a b\u1eb1ng c\u00e1ch s\u1eed d\u1ee5ng b\u1ea3ng li\u00ean k\u1ebft (th\u1ef1c th\u1ec3 li\u00ean k\u1ebft). B\u1ecf qua b\u01b0\u1edbc n\u00e0y s\u1ebd d\u1eabn \u0111\u1ebfn m\u00f4 h\u00ecnh kh\u00f4ng th\u1ec3 tri\u1ec3n khai b\u1eb1ng SQL chu\u1ea9n.<\/p>\n

              \n
            • M\u00f4 h\u00ecnh logic so v\u1edbi m\u00f4 h\u00ecnh v\u1eadt l\u00fd:<\/strong>M\u00f4 h\u00ecnh logic c\u00f3 th\u1ec3 hi\u1ec3n th\u1ecb m\u1ed9t \u0111\u01b0\u1eddng th\u1eb3ng tr\u1ef1c ti\u1ebfp gi\u1eefa hai th\u1ef1c th\u1ec3 v\u1edbi c\u1ea5p \u0111\u1ed9 N:N.<\/li>\n
            • Tri\u1ec3n khai v\u1eadt l\u00fd:<\/strong>\u0110\u01b0\u1eddng n\u1ed1i n\u00e0y ph\u1ea3i \u0111\u01b0\u1ee3c chia t\u00e1ch b\u1eb1ng m\u1ed9t b\u1ea3ng m\u1edbi ch\u1ee9a c\u00e1c kh\u00f3a ngo\u1ea1i t\u1eeb c\u1ea3 hai ph\u00eda.<\/li>\n<\/ul>\n

              3. Quy \u01b0\u1edbc \u0111\u1eb7t t\u00ean kh\u00f4ng nh\u1ea5t qu\u00e1n<\/h3>\n

              S\u1eed d\u1ee5ng c\u00e1c phong c\u00e1ch \u0111\u1eb7t t\u00ean k\u1ebft h\u1ee3p (v\u00ed d\u1ee5 nh\u01b0 customer_id<\/code> so v\u1edbi CustomerID<\/code> so v\u1edbi customerId<\/code>) g\u00e2y nh\u1ea7m l\u1eabn cho c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n khi vi\u1ebft truy v\u1ea5n. M\u1ed9t quy \u01b0\u1edbc \u0111\u1eb7t t\u00ean chu\u1ea9n h\u00f3a n\u00ean \u0111\u01b0\u1ee3c thi\u1ebft l\u1eadp ngay t\u1eeb \u0111\u1ea7u d\u1ef1 \u00e1n.<\/p>\n

                \n
              • Ch\u1eef th\u01b0\u1eddng v\u1edbi d\u1ea5u g\u1ea1ch d\u01b0\u1edbi:<\/strong> order_line_items<\/code><\/li>\n
              • PascalCase:<\/strong> OrderLineItems<\/code><\/li>\n
              • CamelCase:<\/strong> orderLineItems<\/code><\/li>\n<\/ul>\n

                \ud83d\udee0\ufe0f Chi\u1ebfn l\u01b0\u1ee3c x\u00e1c minh<\/h2>\n

                \u0110\u1ec3 \u0111\u1ea3m b\u1ea3o s\u01a1 \u0111\u1ed3 ERD v\u1eabn ch\u00ednh x\u00e1c v\u00e0 c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng \u0111\u01b0\u1ee3c, c\u00e1c b\u01b0\u1edbc x\u00e1c minh c\u1ee5 th\u1ec3 c\u1ea7n \u0111\u01b0\u1ee3c th\u1ef1c hi\u1ec7n trong qu\u00e1 tr\u00ecnh xem x\u00e9t. Nh\u1eefng b\u01b0\u1edbc n\u00e0y gi\u00fap ph\u00e1t hi\u1ec7n c\u00e1c \u0111i\u1ec3m g\u00e2y nh\u1ea7m l\u1eabn tr\u01b0\u1edbc khi l\u01b0\u1ee3c \u0111\u1ed3 \u0111\u01b0\u1ee3c c\u1ed1 \u0111\u1ecbnh.<\/p>\n

                  \n
                • \u0110i\u1ec3m qua c\u00f9ng c\u00e1c b\u00ean li\u00ean quan:<\/strong> Xem x\u00e9t s\u01a1 \u0111\u1ed3 c\u00f9ng ng\u01b0\u1eddi d\u00f9ng kinh doanh \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o c\u00e1c m\u1ed1i quan h\u1ec7 ph\u00f9 h\u1ee3p v\u1edbi m\u00f4 h\u00ecnh t\u01b0 duy c\u1ee7a h\u1ecd v\u1ec1 quy tr\u00ecnh l\u00e0m vi\u1ec7c.<\/li>\n
                • X\u00e1c minh r\u00e0ng bu\u1ed9c:<\/strong> Ki\u1ec3m tra xem m\u1ed7i kh\u00f3a ngo\u1ea1i c\u00f3 tham chi\u1ebfu \u0111\u1ebfn kh\u00f3a ch\u00ednh t\u01b0\u01a1ng \u1ee9ng hay kh\u00f4ng.<\/li>\n
                • T\u00ednh nh\u1ea5t qu\u00e1n v\u1ec1 ki\u1ec3u d\u1eef li\u1ec7u:<\/strong> \u0110\u1ea3m b\u1ea3o r\u1eb1ng c\u00e1c thu\u1ed9c t\u00ednh \u0111\u01b0\u1ee3c \u0111\u1ecbnh ngh\u0129a l\u00e0 s\u1ed1 nguy\u00ean trong m\u1ed9t b\u1ea3ng kh\u00f4ng \u0111\u01b0\u1ee3c \u0111\u1ecbnh ngh\u0129a l\u00e0 chu\u1ed7i trong b\u1ea3ng kh\u00e1c.<\/li>\n
                • Tu\u00e2n th\u1ee7 bi\u1ec3u t\u01b0\u1ee3ng ch\u00fa th\u00edch:<\/strong> X\u00e1c minh r\u1eb1ng t\u1ea5t c\u1ea3 c\u00e1c bi\u1ec3u t\u01b0\u1ee3ng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng trong s\u01a1 \u0111\u1ed3 \u0111\u1ec1u kh\u1edbp v\u1edbi ch\u00fa th\u00edch ho\u1eb7c ti\u00eau chu\u1ea9n \u0111\u01b0\u1ee3c cung c\u1ea5p.<\/li>\n<\/ul>\n

                  \ud83d\udcdd T\u00f3m t\u1eaft c\u00e1c th\u1ef1c h\u00e0nh t\u1ed1t nh\u1ea5t<\/h2>\n

                  Duy tr\u00ec s\u1ef1 r\u00f5 r\u00e0ng trong s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 \u0111\u00f2i h\u1ecfi s\u1ef1 k\u1ef7 lu\u1eadt. B\u1eb1ng c\u00e1ch tu\u00e2n th\u1ee7 k\u00fd hi\u1ec7u chu\u1ea9n, x\u00e1c \u0111\u1ecbnh r\u00f5 r\u00e0ng t\u00ednh cardinality v\u00e0 ph\u00e2n bi\u1ec7t gi\u1eefa c\u00e1c lo\u1ea1i th\u1ef1c th\u1ec3, r\u1ee7i ro hi\u1ec3u nh\u1ea7m s\u1ebd gi\u1ea3m \u0111\u00e1ng k\u1ec3. M\u1ee5c ti\u00eau kh\u00f4ng ch\u1ec9 l\u00e0 v\u1ebd m\u1ed9t b\u1ee9c tranh, m\u00e0 l\u00e0 t\u1ea1o ra m\u1ed9t t\u00e0i li\u1ec7u m\u00f4 t\u1ea3 c\u00f3 th\u1ec3 chuy\u1ec3n \u0111\u1ed5i tr\u1ef1c ti\u1ebfp th\u00e0nh m\u1ed9t h\u1ec7 th\u1ed1ng c\u01a1 s\u1edf d\u1eef li\u1ec7u \u1ed5n \u0111\u1ecbnh v\u00e0 \u0111\u00e1ng tin c\u1eady.<\/p>\n

                  H\u00e3y nh\u1edb r\u1eb1ng s\u01a1 \u0111\u1ed3 l\u00e0 m\u1ed9t t\u00e0i li\u1ec7u s\u1ed1ng. Khi y\u00eau c\u1ea7u thay \u0111\u1ed5i, s\u01a1 \u0111\u1ed3 ERD c\u1ea7n \u0111\u01b0\u1ee3c c\u1eadp nh\u1eadt \u0111\u1ec3 ph\u1ea3n \u00e1nh nh\u1eefng thay \u0111\u1ed5i \u0111\u00f3. \u0110i\u1ec1u n\u00e0y \u0111\u1ea3m b\u1ea3o m\u00f4 h\u00ecnh d\u1eef li\u1ec7u v\u1eabn ti\u1ebfp t\u1ee5c ph\u1ee5c v\u1ee5 doanh nghi\u1ec7p m\u1ed9t c\u00e1ch ch\u00ednh x\u00e1c theo th\u1eddi gian. Vi\u1ec7c xem x\u00e9t \u0111\u1ecbnh k\u1ef3 v\u00e0 tu\u00e2n th\u1ee7 c\u00e1c h\u01b0\u1edbng d\u1eabn c\u1ea5u tr\u00fac \u0111\u01b0\u1ee3c n\u00eau trong b\u00e0i vi\u1ebft n\u00e0y s\u1ebd gi\u00fap c\u00e1c \u0111\u1ed9i ng\u0169 tr\u00e1nh \u0111\u01b0\u1ee3c nh\u1eefng sai l\u1ea7m ph\u1ed5 bi\u1ebfn khi\u1ebfn c\u00e1c d\u1ef1 \u00e1n c\u01a1 s\u1edf d\u1eef li\u1ec7u b\u1ecb \u0111\u00ecnh tr\u1ec7.<\/p>\n","protected":false},"excerpt":{"rendered":"

                  Thi\u1ebft k\u1ebf m\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 c\u01a1 s\u1edf d\u1eef li\u1ec7u v\u1eefng ch\u1eafc \u0111\u00f2i h\u1ecfi s\u1ef1 ch\u00ednh x\u00e1c. S\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 (ERD) \u0111\u00f3ng vai tr\u00f2 nh\u01b0 b\u1ea3n v\u1ebd thi\u1ebft…<\/p>\n","protected":false},"author":1,"featured_media":1632,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_title":"S\u1ef1 nh\u1ea7m l\u1eabn v\u1ec1 c\u00e1c th\u00e0nh ph\u1ea7n ERD: H\u01b0\u1edbng d\u1eabn v\u1ec1 Th\u1ef1c th\u1ec3, M\u1ed1i quan h\u1ec7, Thu\u1ed9c t\u00ednh \ud83e\udde9","_yoast_wpseo_metadesc":"Ph\u00e2n t\u00edch chi ti\u1ebft v\u1ec1 c\u00e1c th\u00e0nh ph\u1ea7n ERD g\u00e2y nh\u1ea7m l\u1eabn. 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H\u1ecdc v\u1ec1 t\u00ednh cardinality, kh\u00f3a v\u00e0 c\u00e1c th\u1ef1c th\u1ec3 y\u1ebfu \u0111\u1ec3 c\u1ea3i thi\u1ec7n \u0111\u1ed9 ch\u00ednh x\u00e1c trong m\u00f4 h\u00ecnh h\u00f3a c\u01a1 s\u1edf 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:\/\/www.viz-note.com\/vi\/erd-elements-confusion-breakdown\/\" \/>\n<meta property=\"og:locale\" content=\"vi_VN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"S\u1ef1 nh\u1ea7m l\u1eabn v\u1ec1 c\u00e1c th\u00e0nh ph\u1ea7n ERD: H\u01b0\u1edbng d\u1eabn v\u1ec1 Th\u1ef1c th\u1ec3, M\u1ed1i quan h\u1ec7, Thu\u1ed9c t\u00ednh \ud83e\udde9\" \/>\n<meta property=\"og:description\" content=\"Ph\u00e2n t\u00edch chi ti\u1ebft v\u1ec1 c\u00e1c th\u00e0nh ph\u1ea7n ERD g\u00e2y nh\u1ea7m l\u1eabn. 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