{"id":1691,"date":"2026-03-26T17:55:23","date_gmt":"2026-03-26T17:55:23","guid":{"rendered":"https:\/\/www.go-diagram.com\/vi\/resolving-many-to-many-relationships-erd-modeling\/"},"modified":"2026-03-26T17:55:23","modified_gmt":"2026-03-26T17:55:23","slug":"resolving-many-to-many-relationships-erd-modeling","status":"publish","type":"post","link":"https:\/\/www.go-diagram.com\/vi\/resolving-many-to-many-relationships-erd-modeling\/","title":{"rendered":"Gi\u1ea3i quy\u1ebft c\u00e1c m\u1ed1i quan h\u1ec7 Nhi\u1ec1u-\u0110a: C\u00e1c k\u1ef9 thu\u1eadt r\u00f5 r\u00e0ng cho m\u00f4 h\u00ecnh h\u00f3a s\u01a1 \u0111\u1ed3 th\u1ef1c th\u1ec3 – m\u1ed1i quan h\u1ec7"},"content":{"rendered":"

Trong b\u1ed1i c\u1ea3nh ki\u1ebfn tr\u00fac d\u1eef li\u1ec7u, \u00edt kh\u00e1i ni\u1ec7m n\u00e0o g\u00e2y nh\u1ea7m l\u1eabn nhi\u1ec1u h\u01a1n m\u1ed1i quan h\u1ec7 Nhi\u1ec1u-\u0110a. Khi thi\u1ebft k\u1ebf s\u01a1 \u0111\u1ed3 th\u1ef1c th\u1ec3 – m\u1ed1i quan h\u1ec7 (ERD), vi\u1ec7c g\u1eb7p ph\u1ea3i t\u00ecnh hu\u1ed1ng m\u1ed9t th\u1ef1c th\u1ec3 k\u1ebft n\u1ed1i v\u1edbi nhi\u1ec1u b\u1ea3n ghi c\u1ee7a th\u1ef1c th\u1ec3 kh\u00e1c v\u00e0 ng\u01b0\u1ee3c l\u1ea1i, \u0111\u00f2i h\u1ecfi m\u1ed9t c\u00e1ch ti\u1ebfp c\u1eadn c\u1ea5u tr\u00fac c\u1ee5 th\u1ec3. C\u00e1c h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u quan h\u1ec7 kh\u00f4ng h\u1ed7 tr\u1ee3 tr\u1ef1c ti\u1ebfp c\u00e1c m\u1ed1i quan h\u1ec7 Nhi\u1ec1u-\u0110a. Ch\u00fang c\u1ea7n m\u1ed9t c\u1ea5u tr\u00fac trung gian \u0111\u1ec3 duy tr\u00ec t\u00ednh to\u00e0n v\u1eb9n d\u1eef li\u1ec7u v\u00e0 \u0111\u1ea3m b\u1ea3o truy v\u1ea5n hi\u1ec7u qu\u1ea3. H\u01b0\u1edbng d\u1eabn n\u00e0y kh\u00e1m ph\u00e1 c\u00e1c ph\u01b0\u01a1ng ph\u00e1p chu\u1ea9n x\u00e1c \u0111\u1ec3 gi\u1ea3i quy\u1ebft nh\u1eefng m\u1ed1i quan h\u1ec7 n\u00e0y, \u0111\u1ea3m b\u1ea3o m\u00f4 h\u00ecnh d\u1eef li\u1ec7u c\u1ee7a b\u1ea1n lu\u00f4n v\u1eefng ch\u1eafc, m\u1edf r\u1ed9ng \u0111\u01b0\u1ee3c v\u00e0 \u0111\u01b0\u1ee3c chu\u1ea9n h\u00f3a.<\/p>\n

D\u00f9 b\u1ea1n \u0111ang thi\u1ebft k\u1ebf h\u1ec7 th\u1ed1ng cho h\u1ed3 s\u01a1 h\u1ecdc t\u1eadp, qu\u1ea3n l\u00fd t\u1ed3n kho hay quy\u1ec1n truy c\u1eadp ng\u01b0\u1eddi d\u00f9ng, c\u00e1c nguy\u00ean t\u1eafc gi\u1ea3i quy\u1ebft c\u00e1c c\u1ea5p \u0111\u1ed9 quan h\u1ec7 n\u00e0y v\u1eabn lu\u00f4n kh\u00f4ng \u0111\u1ed5i. Hi\u1ec3u r\u00f5 c\u01a1 ch\u1ebf n\u1ec1n t\u1ea3ng s\u1ebd ng\u0103n ng\u1eeba c\u00e1c l\u1ed7i ph\u00e1t sinh trong t\u01b0\u01a1ng lai v\u00e0 \u0111\u01a1n gi\u1ea3n h\u00f3a vi\u1ec7c b\u1ea3o tr\u00ec. Ch\u00fang ta s\u1ebd \u0111i xa h\u01a1n c\u00e1c \u0111\u1ecbnh ngh\u0129a b\u1ec1 m\u1eb7t \u0111\u1ec3 xem x\u00e9t c\u00e1c y\u00eau c\u1ea7u c\u1ea5u tr\u00fac, quy t\u1eafc chu\u1ea9n h\u00f3a v\u00e0 chi\u1ebfn l\u01b0\u1ee3c tri\u1ec3n khai \u0111\u1ecbnh ngh\u0129a n\u00ean m\u00f4 h\u00ecnh h\u00f3a d\u1eef li\u1ec7u chuy\u00ean nghi\u1ec7p.<\/p>\n

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

\ud83d\udd0d Hi\u1ec3u v\u1ec1 c\u1ea5p \u0111\u1ed9 quan h\u1ec7 trong ERD<\/h2>\n

C\u1ea5p \u0111\u1ed9 quan h\u1ec7 x\u00e1c \u0111\u1ecbnh m\u1ed1i quan h\u1ec7 s\u1ed1 l\u01b0\u1ee3ng gi\u1eefa c\u00e1c th\u1ef1c th\u1ec3 trong c\u01a1 s\u1edf d\u1eef li\u1ec7u. N\u00f3 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. Trong k\u00fd hi\u1ec7u ERD, \u0111i\u1ec1u n\u00e0y th\u01b0\u1eddng \u0111\u01b0\u1ee3c bi\u1ec3u di\u1ec5n b\u1eb1ng c\u00e1c \u0111\u01b0\u1eddng n\u1ed1i gi\u1eefa c\u00e1c th\u1ef1c th\u1ec3, v\u1edbi h\u00ecnh ch\u00e2n chim (crow\u2019s feet) ch\u1ec9 ph\u00eda “nhi\u1ec1u” v\u00e0 c\u00e1c \u0111\u01b0\u1eddng th\u1eb3ng ho\u1eb7c d\u1ea5u g\u1ea1ch \u0111\u01a1n ch\u1ec9 ph\u00eda “m\u1ed9t”.<\/p>\n

C\u00f3 ba c\u1ea5p \u0111\u1ed9 quan h\u1ec7 ch\u00ednh:<\/p>\n

    \n
  • M\u1ed9t-\u0110\u1ed1i-M\u1ed9t (1:1):<\/strong> M\u1ed9t b\u1ea3n ghi duy nh\u1ea5t trong Th\u1ef1c th\u1ec3 A li\u00ean k\u1ebft v\u1edbi m\u1ed9t b\u1ea3n ghi duy nh\u1ea5t trong Th\u1ef1c th\u1ec3 B. V\u00ed d\u1ee5: M\u1ed9t ng\u01b0\u1eddi v\u00e0 h\u1ed9 chi\u1ebfu c\u1ee7a h\u1ecd.<\/li>\n
  • M\u1ed9t-\u0110\u1ed1i-Nhi\u1ec1u (1:M):<\/strong> M\u1ed9t b\u1ea3n ghi trong Th\u1ef1c th\u1ec3 A li\u00ean k\u1ebft v\u1edbi nhi\u1ec1u b\u1ea3n ghi trong Th\u1ef1c th\u1ec3 B. V\u00ed d\u1ee5: M\u1ed9t kh\u00e1ch h\u00e0ng \u0111\u1eb7t nhi\u1ec1u \u0111\u01a1n h\u00e0ng.<\/li>\n
  • Nhi\u1ec1u-\u0110\u1ed1i-Nhi\u1ec1u (M:N):<\/strong> Nhi\u1ec1u b\u1ea3n ghi trong Th\u1ef1c th\u1ec3 A li\u00ean k\u1ebft v\u1edbi nhi\u1ec1u b\u1ea3n ghi trong Th\u1ef1c th\u1ec3 B. V\u00ed d\u1ee5: Sinh vi\u00ean \u0111\u0103ng k\u00fd nhi\u1ec1u kh\u00f3a h\u1ecdc, v\u00e0 m\u1ed7i kh\u00f3a h\u1ecdc ch\u1ee9a nhi\u1ec1u sinh vi\u00ean.<\/li>\n<\/ul>\n

    Trong khi c\u00e1c m\u1ed1i quan h\u1ec7 1:1 v\u00e0 1:M d\u1ec5 d\u00e0ng tri\u1ec3n khai trong l\u01b0\u1ee3c \u0111\u1ed3 c\u01a1 s\u1edf d\u1eef li\u1ec7u v\u1eadt l\u00fd, m\u1ed1i quan h\u1ec7 M:N l\u1ea1i \u0111\u1eb7t ra th\u00e1ch th\u1ee9c \u0111\u1eb7c bi\u1ec7t. L\u00fd thuy\u1ebft quan h\u1ec7 quy \u0111\u1ecbnh r\u1eb1ng m\u1ed9t \u00f4 trong b\u1ea3ng ch\u1ec9 \u0111\u01b0\u1ee3c ch\u1ee9a gi\u00e1 tr\u1ecb nguy\u00ean t\u1eed. M\u1ed9t li\u00ean k\u1ebft tr\u1ef1c ti\u1ebfp gi\u1eefa hai b\u1ea3ng, n\u01a1i m\u1ed9t h\u00e0ng duy nh\u1ea5t trong B\u1ea3ng A c\u00f3 th\u1ec3 tham chi\u1ebfu \u0111\u1ebfn nhi\u1ec1u h\u00e0ng trong B\u1ea3ng B, vi ph\u1ea1m nguy\u00ean t\u1eafc n\u00e0y \u1edf t\u1ea7ng v\u1eadt l\u00fd.<\/p>\n

    \ud83d\udeab T\u1ea1i sao c\u00e1c m\u1ed1i quan h\u1ec7 Nhi\u1ec1u-\u0110a tr\u1ef1c ti\u1ebfp th\u1ea5t b\u1ea1i trong m\u00f4 h\u00ecnh quan h\u1ec7<\/h2>\n

    M\u00f4 h\u00ecnh quan h\u1ec7, \u0111\u01b0\u1ee3c thi\u1ebft l\u1eadp b\u1edfi E.F. Codd, d\u1ef1a tr\u00ean kh\u00e1i ni\u1ec7m c\u00e1c quan h\u1ec7 (b\u1ea3ng), trong \u0111\u00f3 m\u1ed7i c\u1ed9t \u0111\u1ea1i di\u1ec7n cho m\u1ed9t thu\u1ed9c t\u00ednh c\u1ee5 th\u1ec3 v\u00e0 m\u1ed7i h\u00e0ng \u0111\u1ea1i di\u1ec7n cho m\u1ed9t b\u1ea3n ghi duy nh\u1ea5t. C\u00f3 hai l\u00fd do ch\u00ednh khi\u1ebfn li\u00ean k\u1ebft Nhi\u1ec1u-\u0110a tr\u1ef1c ti\u1ebfp l\u00e0 kh\u00f4ng th\u1ec3 trong c\u01a1 s\u1edf d\u1eef li\u1ec7u quan h\u1ec7 ti\u00eau chu\u1ea9n:<\/p>\n

      \n
    • Thi\u1ebfu h\u1ed7 tr\u1ee3 t\u00edch h\u1ee3p:<\/strong>C\u00e1c \u0111\u1ed9ng c\u01a1 c\u01a1 s\u1edf d\u1eef li\u1ec7u kh\u00f4ng cho ph\u00e9p m\u1ed9t c\u1ed9t kh\u00f3a ngo\u1ea1i l\u01b0u nhi\u1ec1u gi\u00e1 tr\u1ecb. Kh\u00f3a ngo\u1ea1i ph\u1ea3i tr\u1ecf \u0111\u1ebfn m\u1ed9t kh\u00f3a ch\u00ednh duy nh\u1ea5t trong b\u1ea3ng kh\u00e1c. N\u00f3 kh\u00f4ng th\u1ec3 tr\u1ecf \u0111\u1ebfn m\u1ed9t danh s\u00e1ch c\u00e1c kh\u00f3a.<\/li>\n
    • L\u1ed7i ch\u00e8n v\u00e0 x\u00f3a:<\/strong> N\u1ebfu b\u1ea1n c\u1ed1 g\u1eafng l\u01b0u tr\u1eef nhi\u1ec1u ID trong m\u1ed9t \u00f4 duy nh\u1ea5t (v\u00ed d\u1ee5: \u201cStudent_ID: 101, 102, 103\u201d), b\u1ea1n s\u1ebd vi ph\u1ea1m d\u1ea1ng chu\u1ea9n th\u1ee9 nh\u1ea5t (1NF). \u0110i\u1ec1u n\u00e0y khi\u1ebfn vi\u1ec7c truy v\u1ea5n, c\u1eadp nh\u1eadt v\u00e0 x\u00f3a c\u00e1c m\u1ed1i quan h\u1ec7 c\u1ee5 th\u1ec3 tr\u1edf n\u00ean t\u1ed1n k\u00e9m v\u1ec1 m\u1eb7t t\u00ednh to\u00e1n v\u00e0 d\u1ec5 x\u1ea3y ra l\u1ed7i.<\/li>\n<\/ul>\n

      Do \u0111\u00f3, \u0111\u1ec3 l\u01b0u tr\u1eef d\u1eef li\u1ec7u n\u00e0y m\u1ed9t c\u00e1ch hi\u1ec7u qu\u1ea3, m\u1ed1i quan h\u1ec7 b\u1ea3n th\u00e2n ph\u1ea3i \u0111\u01b0\u1ee3c x\u1eed l\u00fd nh\u01b0 m\u1ed9t th\u1ef1c th\u1ec3. Bi\u1ebfn \u0111\u1ed5i n\u00e0y l\u00e0 k\u1ef9 thu\u1eadt c\u1ed1t l\u00f5i \u0111\u1ec3 gi\u1ea3i quy\u1ebft \u0111\u1ed9 ph\u1ee9c t\u1ea1p.<\/p>\n

      \ud83e\uddf1 K\u1ef9 thu\u1eadt 1: Th\u1ef1c th\u1ec3 li\u00ean k\u1ebft (B\u1ea3ng giao nhau)<\/h2>\n

      Gi\u1ea3i ph\u00e1p ti\u00eau chu\u1ea9n \u0111\u1ec3 gi\u1ea3i quy\u1ebft m\u1ed1i quan h\u1ec7 Nhi\u1ec1u-\u0110a l\u00e0 t\u1ea1o ra m\u1ed9t th\u1ef1c th\u1ec3 li\u00ean k\u1ebft, th\u01b0\u1eddng \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 b\u1ea3ng giao nhau ho\u1eb7c b\u1ea3ng c\u1ea7u n\u1ed1i. B\u1ea3ng n\u00e0y n\u1eb1m v\u1eadt l\u00fd gi\u1eefa hai th\u1ef1c th\u1ec3 ch\u00ednh v\u00e0 chia m\u1ed1i k\u1ebft n\u1ed1i tr\u1ef1c ti\u1ebfp th\u00e0nh hai m\u1ed1i quan h\u1ec7 M\u1ed9t-\u0110\u1ed1i-Nhi\u1ec1u.<\/p>\n

      Khi b\u1ea1n gi\u1edbi thi\u1ec7u b\u1ea3ng giao nhau, m\u1ed1i quan h\u1ec7 M:N ban \u0111\u1ea7u \u0111\u01b0\u1ee3c ph\u00e2n r\u00e3 th\u00e0nh:<\/p>\n

        \n
      • M\u1ed1i quan h\u1ec7 M\u1ed9t-\u0110\u1ed1i-Nhi\u1ec1u gi\u1eefa Th\u1ef1c th\u1ec3 A v\u00e0 B\u1ea3ng giao nhau.<\/li>\n
      • M\u1ed1i quan h\u1ec7 M\u1ed9t-\u0110\u1ed1i-Nhi\u1ec1u gi\u1eefa Th\u1ef1c th\u1ec3 B v\u00e0 B\u1ea3ng giao nhau.<\/li>\n<\/ul>\n

        C\u1ea5u tr\u00fac c\u1ee7a B\u1ea3ng giao nhau:<\/strong><\/p>\n

          \n
        • Kh\u00f3a ngo\u1ea1i:<\/strong> N\u00f3 ph\u1ea3i ch\u1ee9a \u00edt nh\u1ea5t hai c\u1ed9t kh\u00f3a ngo\u1ea1i. M\u1ed9t tham chi\u1ebfu \u0111\u1ebfn kh\u00f3a ch\u00ednh c\u1ee7a Th\u1ef1c th\u1ec3 A, v\u00e0 c\u1ed9t kia tham chi\u1ebfu \u0111\u1ebfn kh\u00f3a ch\u00ednh c\u1ee7a Th\u1ef1c th\u1ec3 B.<\/li>\n
        • Kh\u00f3a ch\u00ednh k\u1ebft h\u1ee3p:<\/strong> Th\u01b0\u1eddng th\u00ec s\u1ef1 k\u1ebft h\u1ee3p c\u1ee7a hai kh\u00f3a ngo\u1ea1i n\u00e0y \u0111\u00f3ng vai tr\u00f2 l\u00e0 kh\u00f3a ch\u00ednh cho b\u1ea3ng giao nhau. \u0110i\u1ec1u n\u00e0y \u0111\u1ea3m b\u1ea3o r\u1eb1ng m\u1ed9t c\u1eb7p th\u1ef1c th\u1ec3 c\u1ee5 th\u1ec3 kh\u00f4ng th\u1ec3 \u0111\u01b0\u1ee3c li\u00ean k\u1ebft nhi\u1ec1u h\u01a1n m\u1ed9t l\u1ea7n, tr\u1eeb khi m\u1ed1i quan h\u1ec7 v\u1ed1n d\u0129 l\u00e0 \u0111a gi\u00e1 tr\u1ecb.<\/li>\n
        • Kh\u00f3a thay th\u1ebf:<\/strong>Trong m\u1ed9t s\u1ed1 tr\u01b0\u1eddng h\u1ee3p, m\u1ed9t ID t\u1ef1 t\u0103ng duy nh\u1ea5t \u0111\u01b0\u1ee3c th\u00eam v\u00e0o b\u1ea3ng giao nhau. \u0110i\u1ec1u n\u00e0y h\u1eefu \u00edch n\u1ebfu m\u1ed1i quan h\u1ec7 c\u00f3 th\u1ec3 c\u00f3 nhi\u1ec1u b\u1ea3n ghi kh\u00e1c nhau v\u1edbi c\u00e1c thu\u1ed9c t\u00ednh kh\u00e1c nhau (v\u00ed d\u1ee5: m\u1ed9t sinh vi\u00ean c\u00f3 th\u1ec3 \u0111\u0103ng k\u00fd m\u1ed9t kh\u00f3a h\u1ecdc nhi\u1ec1u l\u1ea7n v\u1edbi c\u00e1c \u0111i\u1ec3m s\u1ed1 kh\u00e1c nhau trong c\u00e1c n\u0103m kh\u00e1c nhau).<\/li>\n<\/ul>\n

          V\u00ed d\u1ee5 t\u00ecnh hu\u1ed1ng:<\/strong><\/p>\n

          X\u00e9t m\u1ed9t h\u1ec7 th\u1ed1ng th\u01b0 vi\u1ec7n. M\u1ed9t S\u00e1ch<\/strong>c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c m\u01b0\u1ee3n b\u1edfi nhi\u1ec1u Ng\u01b0\u1eddi m\u01b0\u1ee3n<\/strong>. M\u1ed9t Ng\u01b0\u1eddi m\u01b0\u1ee3n<\/strong>c\u00f3 th\u1ec3 m\u01b0\u1ee3n nhi\u1ec1u S\u00e1ch<\/strong>.<\/p>\n

            \n
          • Kh\u00f4ng gi\u1ea3i quy\u1ebft: B\u1ea1n kh\u00f4ng th\u1ec3 li\u00ean k\u1ebft m\u1ed9t h\u00e0ng s\u00e1ch v\u1edbi nhi\u1ec1u h\u00e0ng ng\u01b0\u1eddi m\u01b0\u1ee3n tr\u1ef1c ti\u1ebfp.<\/li>\n
          • V\u1edbi gi\u1ea3i ph\u00e1p: T\u1ea1o m\u1ed9t b\u1ea3ng L\u1ecbch_s\u1eed_m\u01b0\u1ee3n<\/strong> b\u1ea3ng.<\/li>\n
          • B\u1ea3ng L\u1ecbch_s\u1eed_m\u01b0\u1ee3n<\/strong>ch\u1ee9a Book_ID<\/code>v\u00e0 Patron_ID<\/code>.<\/li>\n<\/ul>\n

            C\u1ea5u tr\u00fac n\u00e0y cho ph\u00e9p c\u01a1 s\u1edf d\u1eef li\u1ec7u theo d\u00f5i ch\u00ednh x\u00e1c ng\u01b0\u1eddi m\u01b0\u1ee3n n\u00e0o \u0111ang c\u00f3 cu\u1ed1n s\u00e1ch n\u00e0o v\u00e0o b\u1ea5t k\u1ef3 th\u1eddi \u0111i\u1ec3m n\u00e0o m\u00e0 kh\u00f4ng c\u1ea7n sao ch\u00e9p d\u1eef li\u1ec7u s\u00e1ch ho\u1eb7c ng\u01b0\u1eddi m\u01b0\u1ee3n.<\/p>\n

            \ud83d\udcdd K\u1ef9 thu\u1eadt 2: X\u1eed l\u00fd thu\u1ed9c t\u00ednh tr\u00ean m\u1ed1i quan h\u1ec7<\/h2>\n

            S\u1ef1 kh\u00e1c bi\u1ec7t quan tr\u1ecdng trong m\u00f4 h\u00ecnh h\u00f3a ERD l\u00e0 m\u1ed1i quan h\u1ec7 gi\u1eefa c\u00e1c th\u1ef1c th\u1ec3 c\u00f3 mang theo d\u1eef li\u1ec7u ri\u00eang hay kh\u00f4ng. Trong m\u1ed9t li\u00ean k\u1ebft \u0111\u01a1n gi\u1ea3n, m\u1ed1i quan h\u1ec7 t\u1ed3n t\u1ea1i hay kh\u00f4ng t\u1ed3n t\u1ea1i. Tuy nhi\u00ean, trong nhi\u1ec1u t\u00ecnh hu\u1ed1ng th\u1ef1c t\u1ebf, ch\u00ednh m\u1ed1i quan h\u1ec7 \u0111\u00f3 l\u1ea1i c\u00f3 c\u00e1c thu\u1ed9c t\u00ednh.<\/p>\n

            V\u00ed d\u1ee5, trong m\u1ed9t D\u1ef1 \u00e1n<\/strong>v\u00e0 Nh\u00e2n vi\u00ean<\/strong> t\u00ecnh hu\u1ed1ng, m\u1ed9t nh\u00e2n vi\u00ean c\u00f3 th\u1ec3 l\u00e0m vi\u1ec7c tr\u00ean nhi\u1ec1u d\u1ef1 \u00e1n, v\u00e0 m\u1ed9t d\u1ef1 \u00e1n c\u00f3 nhi\u1ec1u nh\u00e2n vi\u00ean. Nh\u01b0ng m\u1ed1i quan h\u1ec7 c\u00f3 th\u1ec3 bao g\u1ed3m:<\/p>\n

              \n
            • Vai tr\u00f2:<\/strong>Nh\u00e2n vi\u00ean n\u00e0y c\u00f3 ph\u1ea3i l\u00e0 nh\u00e0 ph\u00e1t tri\u1ec3n, nh\u00e0 thi\u1ebft k\u1ebf hay qu\u1ea3n l\u00fd trong d\u1ef1 \u00e1n c\u1ee5 th\u1ec3 n\u00e0y kh\u00f4ng?<\/li>\n
            • S\u1ed1 gi\u1edd \u0111\u01b0\u1ee3c ph\u00e2n b\u1ed5:<\/strong>S\u1ed1 gi\u1edd m\u1ed7i tu\u1ea7n \u0111\u01b0\u1ee3c giao cho d\u1ef1 \u00e1n n\u00e0y l\u00e0 bao nhi\u00eau?<\/li>\n
            • Ng\u00e0y b\u1eaft \u0111\u1ea7u:<\/strong>Phi\u00ean giao nhi\u1ec7m v\u1ee5 n\u00e0y b\u1eaft \u0111\u1ea7u khi n\u00e0o?<\/li>\n<\/ul>\n

              N\u1ebfu b\u1ea1n coi m\u1ed1i quan h\u1ec7 ch\u1ec9 \u0111\u01a1n thu\u1ea7n l\u00e0 m\u1ed9t c\u1edd nh\u1ecb ph\u00e2n, b\u1ea1n s\u1ebd m\u1ea5t \u0111i d\u1eef li\u1ec7u thi\u1ebft y\u1ebfu n\u00e0y. B\u1ea3ng giao nhau tr\u1edf th\u00e0nh n\u01a1i l\u00fd t\u01b0\u1edfng \u0111\u1ec3 l\u01b0u tr\u1eef c\u00e1c thu\u1ed9c t\u00ednh n\u00e0y.<\/p>\n

              Quy t\u1eafc tri\u1ec3n khai:<\/strong><\/p>\n

                \n
              • Kh\u00f4ng l\u01b0u tr\u1eef c\u00e1c thu\u1ed9c t\u00ednh m\u1ed1i quan h\u1ec7 trong c\u00e1c th\u1ef1c th\u1ec3 cha. Ch\u00fang kh\u00f4ng thu\u1ed9c v\u1ec1 D\u1ef1 \u00e1n ri\u00eang l\u1ebb, c\u0169ng kh\u00f4ng thu\u1ed9c v\u1ec1 Nh\u00e2n vi\u00ean ri\u00eang l\u1ebb.<\/li>\n
              • \u0110\u1eb7t t\u1ea5t c\u1ea3 d\u1eef li\u1ec7u c\u1ee5 th\u1ec3 cho m\u1ed1i quan h\u1ec7 v\u00e0o b\u1ea3ng giao nhau.<\/li>\n
              • \u0110\u1ea3m b\u1ea3o b\u1ea3ng giao nhau c\u00f3 m\u1ed9t \u0111\u1ecbnh danh duy nh\u1ea5t (h\u1ee3p th\u00e0nh ho\u1eb7c gi\u1ea3 t\u1ea1o) \u0111\u1ec3 cho ph\u00e9p c\u1eadp nh\u1eadt c\u00e1c thu\u1ed9c t\u00ednh n\u00e0y m\u00e0 kh\u00f4ng \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn c\u00e1c th\u1ef1c th\u1ec3 cha.<\/li>\n<\/ul>\n

                C\u00e1ch ti\u1ebfp c\u1eadn n\u00e0y \u0111\u1ea3m b\u1ea3o chu\u1ea9n h\u00f3a d\u1eef li\u1ec7u. N\u1ebfu b\u1ea1n th\u00eam m\u1ed9t c\u1ed9tVai tr\u00f2<\/code> v\u00e0o b\u1ea3ngNh\u00e2n vi\u00ean<\/strong>th\u00ec s\u1ebd t\u1ea1o ra s\u1ef1 tr\u00f9ng l\u1eb7p n\u1ebfu nh\u00e2n vi\u00ean c\u00f3 nhi\u1ec1u vai tr\u00f2 kh\u00e1c nhau tr\u00ean c\u00e1c d\u1ef1 \u00e1n kh\u00e1c nhau. B\u1ea3ng giao nhau t\u00e1ch bi\u1ec7t s\u1ef1 thay \u0111\u1ed5i n\u00e0y.<\/p>\n

                \u2696\ufe0f K\u1ef9 thu\u1eadt 3: Chu\u1ea9n h\u00f3a v\u00e0 to\u00e0n v\u1eb9n d\u1eef li\u1ec7u<\/h2>\n

                Gi\u1ea3i quy\u1ebft c\u00e1c m\u1ed1i quan h\u1ec7 M:N kh\u00f4ng ch\u1ec9 \u0111\u01a1n thu\u1ea7n l\u00e0 li\u00ean k\u1ebft c\u00e1c b\u1ea3ng; \u0111\u00f3 l\u00e0 tu\u00e2n th\u1ee7 c\u00e1c nguy\u00ean t\u1eafc chu\u1ea9n h\u00f3a \u0111\u1ec3 ng\u0103n ng\u1eeba c\u00e1c b\u1ea5t th\u01b0\u1eddng d\u1eef li\u1ec7u. D\u1ea1ng chu\u1ea9n h\u00f3a th\u1ee9 ba (3NF) l\u00e0 m\u1ee5c ti\u00eau ti\u00eau chu\u1ea9n cho h\u1ea7u h\u1ebft c\u00e1c h\u1ec7 th\u1ed1ng giao d\u1ecbch.<\/p>\n

                Y\u00eau c\u1ea7u D\u1ea1ng chu\u1ea9n h\u00f3a th\u1ee9 ba (3NF):<\/strong><\/p>\n

                  \n
                • B\u1ea3ng ph\u1ea3i \u1edf d\u1ea1ng chu\u1ea9n h\u00f3a th\u1ee9 hai (2NF).<\/li>\n
                • T\u1ea5t c\u1ea3 c\u00e1c thu\u1ed9c t\u00ednh kh\u00f4ng ph\u1ea3i kh\u00f3a ph\u1ea3i ph\u1ee5 thu\u1ed9c duy nh\u1ea5t v\u00e0o kh\u00f3a ch\u00ednh.<\/li>\n<\/ul>\n

                  B\u1eb1ng c\u00e1ch t\u1ea1o b\u1ea3ng giao nhau, b\u1ea1n \u0111\u1ea3m b\u1ea3o d\u1eef li\u1ec7u m\u1ed1i quan h\u1ec7 ph\u1ee5 thu\u1ed9c v\u00e0o kh\u00f3a h\u1ee3p th\u00e0nh c\u1ee7a b\u1ea3ng giao nhau, ch\u1ee9 kh\u00f4ng ph\u1ee5 thu\u1ed9c v\u00e0o c\u00e1c kh\u00f3a th\u1ef1c th\u1ec3 ri\u00eang l\u1ebb. \u0110i\u1ec1u n\u00e0y lo\u1ea1i b\u1ecf c\u00e1c ph\u1ee5 thu\u1ed9c b\u1eafc c\u1ea7u.<\/p>\n

                  To\u00e0n v\u1eb9n tham chi\u1ebfu:<\/strong><\/p>\n

                  C\u00e1c r\u00e0ng bu\u1ed9c kh\u00f3a ngo\u1ea1i l\u00e0 thi\u1ebft y\u1ebfu trong b\u1ea3ng giao nhau. Ch\u00fang th\u1ef1c thi c\u00e1c quy t\u1eafc sau:<\/p>\n

                    \n
                  • M\u1ed9tBook_ID<\/code> trong nh\u1eadt k\u00fd m\u01b0\u1ee3n s\u00e1ch ph\u1ea3i t\u1ed3n t\u1ea1i trong b\u1ea3ngS\u00e1ch<\/strong>b\u1ea3ng.<\/li>\n
                  • M\u1ed9t Patron_ID<\/code> trong nh\u1eadt k\u00fd m\u01b0\u1ee3n ph\u1ea3i t\u1ed3n t\u1ea1i trong b\u1ea3ng Patrons<\/strong> b\u1ea3ng.<\/li>\n<\/ul>\n

                    \u0110i\u1ec1u n\u00e0y ng\u0103n ch\u1eb7n c\u00e1c b\u1ea3n ghi b\u1ecb t\u00e1ch r\u1eddi. B\u1ea1n kh\u00f4ng th\u1ec3 ghi s\u1ef1 ki\u1ec7n m\u01b0\u1ee3n cho m\u1ed9t cu\u1ed1n s\u00e1ch kh\u00f4ng t\u1ed3n t\u1ea1i trong danh m\u1ee5c. C\u00e1c h\u1ec7 \u0111\u1ed9ng c\u01a1 c\u01a1 s\u1edf d\u1eef li\u1ec7u th\u1ef1c thi \u0111i\u1ec1u n\u00e0y th\u00f4ng qua h\u00e0nh \u0111\u1ed9ng CASCADE<\/code> ho\u1eb7c RESTRICT<\/code> khi x\u00f3a.<\/p>\n

                    \ud83d\udcca So s\u00e1nh c\u00e1c lo\u1ea1i m\u1ed1i quan h\u1ec7<\/h2>\n

                    Vi\u1ec7c tr\u1ef1c quan h\u00f3a s\u1ef1 kh\u00e1c bi\u1ec7t gi\u1eefa c\u00e1c lo\u1ea1i m\u1ed1i quan h\u1ec7 gi\u00fap l\u1ef1a ch\u1ecdn chi\u1ebfn l\u01b0\u1ee3c m\u00f4 h\u00ecnh h\u00f3a ph\u00f9 h\u1ee3p. B\u1ea3ng d\u01b0\u1edbi \u0111\u00e2y t\u00f3m t\u1eaft c\u00e1c y\u00eau c\u1ea7u c\u1ea5u tr\u00fac v\u00e0 \u0111\u1ed9 ph\u1ee9c t\u1ea1p tri\u1ec3n khai.<\/p>\n\n\n\n\n\n\n\n
                    Lo\u1ea1i m\u1ed1i quan h\u1ec7<\/th>\nTri\u1ec3n khai v\u1eadt l\u00fd<\/th>\nV\u1ecb tr\u00ed kh\u00f3a ch\u00ednh<\/th>\n\u0110\u1ed9 ph\u1ee9c t\u1ea1p<\/th>\n<\/tr>\n<\/thead>\n
                    M\u1ed9t-\u0111\u1ed1i-m\u1ed9t (1:1)<\/td>\nKh\u00f3a ngo\u1ea1i trong m\u1ed9t b\u1ea3ng<\/td>\nB\u1ea5t k\u1ef3 b\u1ea3ng n\u00e0o<\/td>\nTh\u1ea5p<\/td>\n<\/tr>\n
                    M\u1ed9t-\u0111\u1ed1i-nhi\u1ec1u (1:M)<\/td>\nKh\u00f3a ngo\u1ea1i trong b\u1ea3ng \u201cnhi\u1ec1u\u201d<\/td>\nB\u1ea3ng ch\u00ednh<\/td>\nTrung b\u00ecnh<\/td>\n<\/tr>\n
                    Nhi\u1ec1u-\u0111\u1ed1i-nhi\u1ec1u (M:N)<\/td>\nB\u1ea3ng li\u00ean k\u1ebft ri\u00eang bi\u1ec7t<\/td>\nB\u1ea3ng li\u00ean k\u1ebft (h\u1ee3p th\u00e0nh)<\/td>\nCao<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

                    Nh\u01b0 \u0111\u00e3 th\u1ea5y, m\u1ed1i quan h\u1ec7 M:N \u0111\u00f2i h\u1ecfi chi ph\u00ed c\u1ea5u tr\u00fac l\u1edbn nh\u1ea5t. Tuy nhi\u00ean, chi ph\u00ed n\u00e0y l\u00e0 c\u1ea7n thi\u1ebft \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o t\u00ednh to\u00e0n v\u1eb9n d\u1eef li\u1ec7u. Chi ph\u00ed c\u1ee7a m\u1ed9t ph\u00e9p n\u1ed1i th\u00eam trong truy v\u1ea5n th\u01b0\u1eddng b\u1ecb v\u01b0\u1ee3t qua b\u1edfi chi ph\u00ed do s\u1ef1 b\u1ea5t nh\u1ea5t d\u1eef li\u1ec7u trong m\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 \u0111\u01b0\u1ee3c m\u00f4 h\u00ecnh h\u00f3a k\u00e9m.<\/p>\n

                    \ud83d\ude80 Xem x\u00e9t v\u1ec1 hi\u1ec7u su\u1ea5t<\/h2>\n

                    Vi\u1ec7c th\u00eam m\u1ed9t b\u1ea3ng giao nhau s\u1ebd t\u1ea1o ra m\u1ed9t l\u1edbp gi\u00e1n ti\u1ebfp trong truy v\u1ea5n c\u1ee7a b\u1ea1n. Khi truy xu\u1ea5t d\u1eef li\u1ec7u, b\u1ea1n ph\u1ea3i k\u1ebft h\u1ee3p ba b\u1ea3ng thay v\u00ec hai b\u1ea3ng. Trong c\u00e1c h\u1ec7 th\u1ed1ng c\u00f3 kh\u1ed1i l\u01b0\u1ee3ng l\u1edbn, \u0111i\u1ec1u n\u00e0y c\u00f3 th\u1ec3 \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn hi\u1ec7u su\u1ea5t n\u1ebfu kh\u00f4ng \u0111\u01b0\u1ee3c qu\u1ea3n l\u00fd \u0111\u00fang c\u00e1ch.<\/p>\n

                      \n
                    • Ch\u1ec9 m\u1ee5c:<\/strong>M\u1ed7i kh\u00f3a ngo\u1ea1i trong b\u1ea3ng giao nhau \u0111\u1ec1u n\u00ean \u0111\u01b0\u1ee3c ch\u1ec9 m\u1ee5c. \u0110i\u1ec1u n\u00e0y gi\u00fap \u0111\u1ed9ng c\u01a1 c\u01a1 s\u1edf d\u1eef li\u1ec7u nhanh ch\u00f3ng t\u00ecm ki\u1ebfm c\u00e1c h\u00e0ng cho m\u1ed9t th\u1ef1c th\u1ec3 c\u1ee5 th\u1ec3 m\u00e0 kh\u00f4ng c\u1ea7n qu\u00e9t to\u00e0n b\u1ed9 b\u1ea3ng giao nhau.<\/li>\n
                    • Ch\u1ec9 m\u1ee5c k\u1ebft h\u1ee3p:<\/strong>Trong m\u1ed9t s\u1ed1 tr\u01b0\u1eddng h\u1ee3p, vi\u1ec7c t\u1ea1o ch\u1ec9 m\u1ee5c tr\u00ean t\u1ed5 h\u1ee3p c\u1ee7a c\u1ea3 hai kh\u00f3a ngo\u1ea1i s\u1ebd hi\u1ec7u qu\u1ea3 h\u01a1n so v\u1edbi vi\u1ec7c t\u1ea1o c\u00e1c ch\u1ec9 m\u1ee5c ri\u00eang bi\u1ec7t. \u0110i\u1ec1u n\u00e0y h\u1ed7 tr\u1ee3 c\u00e1c truy v\u1ea5n l\u1ecdc theo c\u1ea3 hai th\u1ef1c th\u1ec3 c\u00f9ng l\u00fac.<\/li>\n
                    • \u0110\u1ecdc so v\u1edbi Ghi:<\/strong>B\u1ea3ng giao nhau th\u01b0\u1eddng c\u00f3 ho\u1ea1t \u0111\u1ed9ng ghi nhi\u1ec1u n\u1ebfu c\u00e1c m\u1ed1i quan h\u1ec7 l\u00e0 \u0111\u1ed9ng. Ch\u00fang th\u01b0\u1eddng c\u00f3 ho\u1ea1t \u0111\u1ed9ng \u0111\u1ecdc nhi\u1ec1u khi t\u1ea1o b\u00e1o c\u00e1o. \u0110\u1ea3m b\u1ea3o chi\u1ebfn l\u01b0\u1ee3c ch\u1ec9 m\u1ee5c c\u1ee7a b\u1ea1n h\u1ed7 tr\u1ee3 m\u1eabu thao t\u00e1c ch\u1ee7 \u0111\u1ea1o trong \u1ee9ng d\u1ee5ng c\u1ee7a b\u1ea1n.<\/li>\n<\/ul>\n

                      \u26a0\ufe0f Nh\u1eefng sai l\u1ea7m ph\u1ed5 bi\u1ebfn v\u00e0 gi\u1ea3i ph\u00e1p<\/h2>\n

                      Ngay c\u1ea3 nh\u1eefng ng\u01b0\u1eddi m\u00f4 h\u00ecnh h\u00f3a c\u00f3 kinh nghi\u1ec7m c\u0169ng m\u1eafc sai l\u1ea7m khi gi\u1ea3i quy\u1ebft c\u00e1c m\u1ed1i quan h\u1ec7 b\u1eadc. Nh\u1eadn th\u1ee9c v\u1ec1 nh\u1eefng l\u1ed7i ph\u1ed5 bi\u1ebfn c\u00f3 th\u1ec3 gi\u00fap ti\u1ebft ki\u1ec7m th\u1eddi gian t\u00e1i c\u1ea5u tr\u00fac \u0111\u00e1ng k\u1ec3 sau n\u00e0y.<\/p>\n

                      1. Sai l\u1ea7m ‘M\u1ed9t c\u1ed9t’<\/h3>\n

                      C\u1ed1 g\u1eafng l\u01b0u tr\u1eef nhi\u1ec1u ID trong m\u1ed9t c\u1ed9t duy nh\u1ea5t b\u1eb1ng c\u00e1ch s\u1eed d\u1ee5ng c\u00e1c gi\u00e1 tr\u1ecb ph\u00e2n c\u00e1ch b\u1eb1ng d\u1ea5u ph\u1ea9y (v\u00ed d\u1ee5: \u201c1, 2, 3\u201d). \u0110i\u1ec1u n\u00e0y vi ph\u1ea1m c\u00e1c nguy\u00ean t\u1eafc c\u01a1 s\u1edf d\u1eef li\u1ec7u v\u00e0 khi\u1ebfn vi\u1ec7c truy v\u1ea5n tr\u1edf n\u00ean kh\u00f4ng th\u1ec3 th\u1ef1c hi\u1ec7n \u0111\u01b0\u1ee3c m\u00e0 kh\u00f4ng d\u00f9ng h\u00e0m ph\u00e2n t\u00edch chu\u1ed7i. Lu\u00f4n s\u1eed d\u1ee5ng m\u1ed9t h\u00e0ng ri\u00eang bi\u1ec7t cho m\u1ed7i tr\u01b0\u1eddng h\u1ee3p m\u1ed1i quan h\u1ec7.<\/p>\n

                      2. Thu\u1ed9c t\u00ednh tr\u00f9ng l\u1eb7p<\/h3>\n

                      Sao ch\u00e9p c\u00e1c thu\u1ed9c t\u00ednh t\u1eeb c\u00e1c th\u1ef1c th\u1ec3 cha v\u00e0o b\u1ea3ng giao nhau m\u1ed9t c\u00e1ch kh\u00f4ng c\u1ea7n thi\u1ebft. N\u1ebfu m\u1ed9t thu\u1ed9c t\u00ednh thu\u1ed9c v\u1ec1 th\u1ef1c th\u1ec3 (v\u00ed d\u1ee5: T\u00ean sinh vi\u00ean), th\u00ec n\u00f3 ph\u1ea3i n\u1eb1m trong b\u1ea3ng Sinh vi\u00ean, ch\u1ee9 kh\u00f4ng ph\u1ea3i trong b\u1ea3ng \u0110\u0103ng k\u00fd. Ch\u1ec9 \u0111\u1eb7t d\u1eef li\u1ec7u m\u00f4 t\u1ea3 ch\u00ednh m\u1ed1i quan h\u1ec7 \u0111\u00f3.<\/p>\n

                      3. B\u1ecf qua t\u00ednh kh\u1ea3 d\u1ee5ng c\u1ee7a gi\u00e1 tr\u1ecb null<\/h3>\n

                      \u0110\u1ecbnh ngh\u0129a c\u00e1c kh\u00f3a ngo\u1ea1i l\u00e0 c\u00f3 th\u1ec3 null khi ch\u00fang ph\u1ea3i l\u00e0 b\u1eaft bu\u1ed9c. N\u1ebfu m\u1ed9t m\u1ed1i quan h\u1ec7 l\u00e0 b\u1eaft bu\u1ed9c (v\u00ed d\u1ee5: m\u1ed9t \u0110\u01a1n h\u00e0ng ph\u1ea3i c\u00f3 Kh\u00e1ch h\u00e0ng), th\u00ec kh\u00f3a ngo\u1ea1i kh\u00f4ng \u0111\u01b0\u1ee3c ph\u00e9p c\u00f3 gi\u00e1 tr\u1ecb null. \u0110i\u1ec1u n\u00e0y \u0111\u1ea3m b\u1ea3o c\u00e1c quy t\u1eafc kinh doanh \u0111\u01b0\u1ee3c \u00e1p d\u1ee5ng \u1edf c\u1ea5p \u0111\u1ed9 c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/p>\n

                      4. Tham chi\u1ebfu v\u00f2ng l\u1eb7p<\/h3>\n

                      T\u1ea1o m\u1ed9t b\u1ea3ng giao nhau tham chi\u1ebfu l\u1ea1i ch\u00ednh n\u00f3 m\u1ed9t c\u00e1ch kh\u00f4ng c\u1ea7n thi\u1ebft. \u0110\u1ea3m b\u1ea3o b\u1ea3ng giao nhau ch\u1ec9 k\u1ebft n\u1ed1i hai th\u1ef1c th\u1ec3 ri\u00eang bi\u1ec7t tham gia v\u00e0o m\u1ed1i quan h\u1ec7. Tr\u00e1nh t\u1ea1o c\u00e1c v\u00f2ng l\u1eb7p kh\u00f4ng ph\u1ee5c v\u1ee5 m\u1ee5c \u0111\u00edch ch\u1ee9c n\u0103ng n\u00e0o.<\/p>\n

                      \ud83c\udfa8 C\u00e1c nguy\u00ean t\u1eafc t\u1ed1t nh\u1ea5t v\u1ec1 bi\u1ec3u di\u1ec5n tr\u1ef1c quan<\/h2>\n

                      Khi t\u00e0i li\u1ec7u h\u00f3a s\u01a1 \u0111\u1ed3 ERD c\u1ee7a b\u1ea1n, s\u1ef1 r\u00f5 r\u00e0ng l\u00e0 \u0111i\u1ec1u t\u1ed1i quan tr\u1ecdng. Bi\u1ec3u di\u1ec5n tr\u1ef1c quan ph\u1ea3i ngay l\u1eadp t\u1ee9c truy\u1ec1n \u0111\u1ea1t c\u1ea5u tr\u00fac \u0111\u00e3 \u0111\u01b0\u1ee3c gi\u1ea3i quy\u1ebft cho b\u1ea5t k\u1ef3 ai \u0111\u1ecdc s\u01a1 \u0111\u1ed3.<\/p>\n

                        \n
                      • \u0110\u1eb7t nh\u00e3n cho b\u1ea3ng giao nhau:<\/strong>\u0110\u1eb7t t\u00ean b\u1ea3ng m\u1ed9t c\u00e1ch m\u00f4 t\u1ea3. Thay v\u00ec \u201cTable3\u201d, h\u00e3y d\u00f9ng \u201cSinh_Vien_Khoa_Hoc_Dang_Ky\u201d.<\/li>\n
                      • Ch\u1ec9 r\u00f5 b\u1eadc m\u1ed1i quan h\u1ec7:<\/strong>R\u00f5 r\u00e0ng \u0111\u00e1nh d\u1ea5u c\u00e1c \u0111\u01b0\u1eddng n\u1ed1i b\u1ea3ng giao nhau v\u1edbi c\u00e1c th\u1ef1c th\u1ec3 cha. S\u1eed d\u1ee5ng k\u00fd hi\u1ec7u ch\u00e2n chim \u1edf ph\u00eda b\u1ea3ng giao nhau \u0111\u1ec3 th\u1ec3 hi\u1ec7n m\u1ed1i quan h\u1ec7 ‘nhi\u1ec1u’ theo quan \u0111i\u1ec3m c\u1ee7a th\u1ef1c th\u1ec3 cha.<\/li>\n
                      • Hi\u1ec7n c\u00e1c thu\u1ed9c t\u00ednh:<\/strong>N\u1ebfu b\u1ea3ng giao nhau c\u00f3 c\u00e1c thu\u1ed9c t\u00ednh (nh\u01b0 \u201c\u0110i\u1ec3m\u201d ho\u1eb7c \u201cNg\u00e0y\u201d), h\u00e3y li\u1ec7t k\u00ea ch\u00fang r\u00f5 r\u00e0ng trong s\u01a1 \u0111\u1ed3. \u0110i\u1ec1u n\u00e0y nh\u1ea5n m\u1ea1nh r\u1eb1ng m\u1ed1i quan h\u1ec7 kh\u00f4ng ch\u1ec9 \u0111\u01a1n thu\u1ea7n l\u00e0 m\u1ed9t li\u00ean k\u1ebft.<\/li>\n
                      • S\u1eed d\u1ee5ng c\u00e1c ki\u1ec3u \u0111\u01b0\u1eddng kh\u00e1c nhau:<\/strong>M\u1ed9t s\u1ed1 c\u00f4ng c\u1ee5 m\u00f4 h\u00ecnh h\u00f3a cho ph\u00e9p d\u00f9ng \u0111\u01b0\u1eddng n\u00e9t \u0111\u1ee9t cho c\u00e1c m\u1ed1i quan h\u1ec7 t\u00f9y ch\u1ecdn v\u00e0 \u0111\u01b0\u1eddng n\u00e9t li\u1ec1n cho c\u00e1c m\u1ed1i quan h\u1ec7 b\u1eaft bu\u1ed9c. S\u1ef1 nh\u1ea5t qu\u00e1n \u1edf \u0111\u00e2y gi\u00fap d\u1ec5 hi\u1ec3u h\u01a1n.<\/li>\n<\/ul>\n

                        \ud83d\udd04 M\u1ed1i quan h\u1ec7 \u0111\u1ec7 quy v\u00e0 M:N<\/h2>\n

                        Th\u1ec9nh tho\u1ea3ng, m\u1ed9t m\u1ed1i quan h\u1ec7 nhi\u1ec1u-\u0111a t\u1ed3n t\u1ea1i trong m\u1ed9t th\u1ef1c th\u1ec3 duy nh\u1ea5t. V\u00ed d\u1ee5, m\u1ed9t Nh\u00e2n vi\u00ean<\/strong> c\u00f3 th\u1ec3 qu\u1ea3n l\u00fd nhi\u1ec1u ng\u01b0\u1eddi kh\u00e1c Nh\u00e2n vi\u00ean<\/strong>, v\u00e0 nh\u1eefng nh\u00e2n vi\u00ean n\u00e0y c\u00f3 th\u1ec3 qu\u1ea3n l\u00fd ng\u01b0\u1eddi kh\u00e1c. \u0110\u00e2y l\u00e0 m\u1ed9t m\u1ed1i quan h\u1ec7 M:N \u0111\u1ec7 quy.<\/p>\n

                        Vi\u1ec7c gi\u1ea3i quy\u1ebft v\u1eabn gi\u1ed1ng nh\u01b0 m\u1ed1i quan h\u1ec7 M:N ti\u00eau chu\u1ea9n. B\u1ea1n v\u1eabn c\u1ea7n t\u1ea1o m\u1ed9t b\u1ea3ng li\u00ean k\u1ebft, nh\u01b0ng c\u1ea3 hai kh\u00f3a ngo\u1ea1i trong b\u1ea3ng n\u00e0y \u0111\u1ec1u tham chi\u1ebfu \u0111\u1ebfn kh\u00f3a ch\u00ednh c\u1ee7a c\u00f9ng m\u1ed9t th\u1ef1c th\u1ec3.<\/p>\n

                          \n
                        • Th\u1ef1c th\u1ec3:<\/strong> Nh\u00e2n vi\u00ean<\/li>\n
                        • B\u1ea3ng li\u00ean k\u1ebft:<\/strong>Qu\u1ea3n l\u00fd_Nh\u00e2n_vi\u00ean<\/li>\n
                        • FK1:<\/strong>ID_Tr\u01b0\u1edfng_b\u1ed9_ph\u1eadn (Tham chi\u1ebfu \u0111\u1ebfn Nh\u00e2n vi\u00ean)<\/li>\n
                        • FK2:<\/strong>ID_Ph\u1ee5_thu\u1ed9c (Tham chi\u1ebfu \u0111\u1ebfn Nh\u00e2n vi\u00ean)<\/li>\n<\/ul>\n

                          C\u1ea5u tr\u00fac n\u00e0y cho ph\u00e9p x\u00e2y d\u1ef1ng c\u00e1c c\u1ea5u tr\u00fac t\u1ed5 ch\u1ee9c ph\u1ee9c t\u1ea1p m\u00e0 kh\u00f4ng vi ph\u1ea1m c\u00e1c quy t\u1eafc chu\u1ea9n h\u00f3a. N\u00f3 cho ph\u00e9p th\u1ef1c hi\u1ec7n c\u00e1c truy v\u1ea5n \u0111\u1ec3 \u0111i qua nhi\u1ec1u c\u1ea5p \u0111\u1ed9 s\u00e2u trong qu\u1ea3n l\u00fd.<\/p>\n

                          \ud83d\udee1\ufe0f C\u00e1c r\u00e0ng bu\u1ed9c d\u1eef li\u1ec7u v\u00e0 quy t\u1eafc kinh doanh<\/h2>\n

                          C\u00e1c r\u00e0ng bu\u1ed9c k\u1ef9 thu\u1eadt l\u00e0 ch\u01b0a \u0111\u1ee7; c\u00e1c quy t\u1eafc kinh doanh ph\u1ea3i \u0111\u01b0\u1ee3c th\u1ef1c thi. B\u1ea3ng li\u00ean k\u1ebft cung c\u1ea5p m\u1ed9t v\u1ecb tr\u00ed t\u1ef1 nhi\u00ean \u0111\u1ec3 \u00e1p d\u1ee5ng c\u00e1c quy t\u1eafc n\u00e0y.<\/p>\n

                            \n
                          • R\u00e0ng bu\u1ed9c duy nh\u1ea5t:<\/strong> \u0110\u1ea3m b\u1ea3o r\u1eb1ng m\u1ed9t m\u1ed1i quan h\u1ec7 c\u1ee5 th\u1ec3 kh\u00f4ng th\u1ec3 \u0111\u01b0\u1ee3c t\u1ea1o hai l\u1ea7n tr\u1eeb khi c\u00f3 \u00fd \u0111\u1ecbnh. V\u00ed d\u1ee5, m\u1ed9t sinh vi\u00ean kh\u00f4ng n\u00ean \u0111\u0103ng k\u00fd c\u00f9ng m\u1ed9t l\u1edbp h\u1ecdc trong c\u00f9ng m\u1ed9t h\u1ecdc k\u1ef3 hai l\u1ea7n. M\u1ed9t r\u00e0ng bu\u1ed9c duy nh\u1ea5t tr\u00ean t\u1ed5 h\u1ee3p Student_ID v\u00e0 Course_ID s\u1ebd th\u1ef1c thi \u0111i\u1ec1u n\u00e0y.<\/li>\n
                          • R\u00e0ng bu\u1ed9c ki\u1ec3m tra:<\/strong> X\u00e1c th\u1ef1c d\u1eef li\u1ec7u s\u1ed1. V\u00ed d\u1ee5, \u201cS\u1ed1 gi\u1edd \u0111\u01b0\u1ee3c ph\u00e2n b\u1ed5\u201d trong b\u1ea3ng li\u00ean k\u1ebft d\u1ef1 \u00e1n ph\u1ea3i l\u1edbn h\u01a1n 0 v\u00e0 nh\u1ecf h\u01a1n 40.<\/li>\n
                          • B\u1ed9 k\u00edch ho\u1ea1t:<\/strong> Trong c\u00e1c h\u1ec7 th\u1ed1ng ph\u1ee9c t\u1ea1p, c\u00f3 th\u1ec3 c\u1ea7n s\u1eed d\u1ee5ng b\u1ed9 k\u00edch ho\u1ea1t \u0111\u1ec3 c\u1eadp nh\u1eadt c\u00e1c b\u1ea3ng t\u00f3m t\u1eaft. N\u1ebfu b\u1ea3ng li\u00ean k\u1ebft thay \u0111\u1ed5i, b\u1ea3ng t\u00f3m t\u1eaft trong th\u1ef1c th\u1ec3 cha (v\u00ed d\u1ee5: \u201cT\u1ed5ng_s\u1ed1_d\u1ef1_\u00e1n_theo_m\u1ed7i_nh\u00e2n_vi\u00ean\u201d) c\u00f3 th\u1ec3 c\u1ea7n \u0111\u01b0\u1ee3c c\u1eadp nh\u1eadt t\u1ef1 \u0111\u1ed9ng.<\/li>\n<\/ul>\n

                            \ud83d\udcc8 S\u1ef1 ph\u00e1t tri\u1ec3n c\u1ee7a m\u00f4 h\u00ecnh<\/h2>\n

                            C\u00e1c m\u00f4 h\u00ecnh ph\u00e1t tri\u1ec3n theo s\u1ef1 thay \u0111\u1ed5i y\u00eau c\u1ea7u. M\u1ed9t m\u1ed1i quan h\u1ec7 ban \u0111\u1ea7u l\u00e0 nhi\u1ec1u-\u0111\u1ebfn-nhi\u1ec1u c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c \u0111\u01a1n gi\u1ea3n h\u00f3a th\u00e0nh m\u1ed9t-\u0111\u1ebfn-nhi\u1ec1u n\u1ebfu quy t\u1eafc kinh doanh thay \u0111\u1ed5i. V\u00ed d\u1ee5, n\u1ebfu ch\u00ednh s\u00e1ch thay \u0111\u1ed5i sao cho m\u1ed9t sinh vi\u00ean ch\u1ec9 \u0111\u01b0\u1ee3c \u0111\u0103ng k\u00fd m\u1ed9t kh\u00f3a h\u1ecdc t\u1ea1i m\u1ed9t th\u1eddi \u0111i\u1ec3m, b\u1ea3ng li\u00ean k\u1ebft c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c h\u1ee3p nh\u1ea5t tr\u1edf l\u1ea1i v\u00e0o b\u1ea3ng sinh vi\u00ean.<\/p>\n

                            Tuy nhi\u00ean, b\u1eaft \u0111\u1ea7u b\u1eb1ng b\u1ea3ng li\u00ean k\u1ebft th\u01b0\u1eddng an to\u00e0n h\u01a1n. N\u00f3 \u0111\u00e1p \u1ee9ng \u0111\u01b0\u1ee3c m\u1ee9c \u0111\u1ed9 linh ho\u1ea1t t\u1ed1i \u0111a. N\u1ebfu y\u00eau c\u1ea7u thay \u0111\u1ed5i sau n\u00e0y \u0111\u1ec3 cho ph\u00e9p \u0111\u0103ng k\u00fd nhi\u1ec1u l\u1ea7n, l\u01b0\u1ee3c \u0111\u1ed3 \u0111\u00e3 s\u1eb5n s\u00e0ng. N\u1ebfu b\u1ea1n b\u1eaft \u0111\u1ea7u b\u1eb1ng b\u1ea3ng \u0111\u00e3 h\u1ee3p nh\u1ea5t, b\u1ea1n s\u1ebd ph\u1ea3i t\u00e1i c\u1ea5u tr\u00fac sau n\u00e0y.<\/p>\n

                            \ud83d\udcdd T\u00f3m t\u1eaft nh\u1eefng \u0111i\u1ec3m ch\u00ednh<\/h2>\n

                            Gi\u1ea3i quy\u1ebft c\u00e1c m\u1ed1i quan h\u1ec7 nhi\u1ec1u-\u0111\u1ebfn-nhi\u1ec1u l\u00e0 k\u1ef9 n\u0103ng c\u01a1 b\u1ea3n trong thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u. N\u00f3 \u0111\u00f2i h\u1ecfi vi\u1ec7c t\u1ea1o ra m\u1ed9t c\u1ea5u tr\u00fac trung gian \u0111\u1ec3 duy tr\u00ec t\u00ednh to\u00e0n v\u1eb9n d\u1eef li\u1ec7u v\u00e0 h\u1ed7 tr\u1ee3 c\u00e1c truy v\u1ea5n hi\u1ec7u qu\u1ea3. B\u1ea3ng li\u00ean k\u1ebft l\u00e0 gi\u1ea3i ph\u00e1p ti\u00eau chu\u1ea9n, chia nh\u1ecf c\u00e1c m\u1ed1i quan h\u1ec7 ph\u1ee9c t\u1ea1p th\u00e0nh c\u00e1c li\u00ean k\u1ebft m\u1ed9t-\u0111\u1ebfn-nhi\u1ec1u d\u1ec5 qu\u1ea3n l\u00fd.<\/p>\n

                              \n
                            • Lu\u00f4n gi\u1ea3i quy\u1ebft m\u1ed1i quan h\u1ec7 M:N:<\/strong> Kh\u00f4ng bao gi\u1edd c\u1ed1 g\u1eafng l\u01b0u tr\u1eef nhi\u1ec1u kh\u00f3a ngo\u1ea1i trong m\u1ed9t c\u1ed9t duy nh\u1ea5t.<\/li>\n
                            • S\u1eed d\u1ee5ng kh\u00f3a h\u1ee3p th\u00e0nh:<\/strong> S\u1ef1 k\u1ebft h\u1ee3p c\u1ee7a c\u00e1c kh\u00f3a ngo\u1ea1i th\u01b0\u1eddng \u0111\u00f3ng vai tr\u00f2 l\u00e0 \u0111\u1ecbnh danh duy nh\u1ea5t cho m\u1ed1i quan h\u1ec7.<\/li>\n
                            • L\u01b0u tr\u1eef d\u1eef li\u1ec7u m\u1ed1i quan h\u1ec7:<\/strong>\u0110\u1eb7t c\u00e1c thu\u1ed9c t\u00ednh c\u1ee5 th\u1ec3 cho li\u00ean k\u1ebft v\u00e0o b\u1ea3ng giao nhau.<\/li>\n
                            • Ch\u1ec9 m\u1ee5c c\u00e1c kh\u00f3a ngo\u1ea1i:<\/strong>Hi\u1ec7u su\u1ea5t ph\u1ee5 thu\u1ed9c v\u00e0o vi\u1ec7c tra c\u1ee9u nhanh c\u00e1c h\u00e0ng trong b\u1ea3ng giao nhau.<\/li>\n
                            • Th\u1ef1c thi c\u00e1c r\u00e0ng bu\u1ed9c:<\/strong>S\u1eed d\u1ee5ng c\u00e1c r\u00e0ng bu\u1ed9c duy nh\u1ea5t v\u00e0 tham chi\u1ebfu kh\u00f3a ngo\u1ea1i \u0111\u1ec3 ng\u0103n d\u1eef li\u1ec7u kh\u00f4ng h\u1ee3p l\u1ec7.<\/li>\n<\/ul>\n

                              B\u1eb1ng c\u00e1ch tu\u00e2n theo c\u00e1c k\u1ef9 thu\u1eadt n\u00e0y, b\u1ea1n \u0111\u1ea3m b\u1ea3o r\u1eb1ng l\u01b0\u1ee3c \u0111\u1ed3 c\u01a1 s\u1edf d\u1eef li\u1ec7u c\u1ee7a b\u1ea1n c\u00f3 kh\u1ea3 n\u0103ng ch\u1ed1ng ch\u1ecbu v\u1edbi s\u1ef1 thay \u0111\u1ed5i v\u00e0 c\u00f3 th\u1ec3 x\u1eed l\u00fd c\u00e1c t\u01b0\u01a1ng t\u00e1c d\u1eef li\u1ec7u ph\u1ee9c t\u1ea1p. C\u00f4ng s\u1ee9c \u0111\u1ea7u t\u01b0 v\u00e0o m\u00f4 h\u00ecnh h\u00f3a \u0111\u00fang \u0111\u1eafn trong giai \u0111o\u1ea1n thi\u1ebft k\u1ebf s\u1ebd mang l\u1ea1i l\u1ee3i \u00edch v\u1ec1 kh\u1ea3 n\u0103ng b\u1ea3o tr\u00ec v\u00e0 hi\u1ec7u su\u1ea5t trong su\u1ed1t v\u00f2ng \u0111\u1eddi c\u1ee7a h\u1ec7 th\u1ed1ng.<\/p>\n","protected":false},"excerpt":{"rendered":"

                              Trong b\u1ed1i c\u1ea3nh ki\u1ebfn tr\u00fac d\u1eef li\u1ec7u, \u00edt kh\u00e1i ni\u1ec7m n\u00e0o g\u00e2y nh\u1ea7m l\u1eabn nhi\u1ec1u h\u01a1n m\u1ed1i quan h\u1ec7 Nhi\u1ec1u-\u0110a. Khi thi\u1ebft k\u1ebf s\u01a1 \u0111\u1ed3 th\u1ef1c th\u1ec3 – m\u1ed1i quan…<\/p>\n","protected":false},"author":1,"featured_media":1692,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_title":"Gi\u1ea3i quy\u1ebft c\u00e1c m\u1ed1i quan h\u1ec7 Nhi\u1ec1u-\u0110a trong m\u00f4 h\u00ecnh h\u00f3a ERD","_yoast_wpseo_metadesc":"H\u1ecdc c\u00e1c k\u1ef9 thu\u1eadt r\u00f5 r\u00e0ng \u0111\u1ec3 gi\u1ea3i quy\u1ebft c\u00e1c m\u1ed1i quan h\u1ec7 Nhi\u1ec1u-\u0110a trong m\u00f4 h\u00ecnh h\u00f3a ERD. 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