{"id":1625,"date":"2026-04-09T08:57:53","date_gmt":"2026-04-09T08:57:53","guid":{"rendered":"https:\/\/www.viz-note.com\/vi\/hidden-complexity-gap-junior-engineers-erd\/"},"modified":"2026-04-09T08:57:53","modified_gmt":"2026-04-09T08:57:53","slug":"hidden-complexity-gap-junior-engineers-erd","status":"publish","type":"post","link":"https:\/\/www.viz-note.com\/vi\/hidden-complexity-gap-junior-engineers-erd\/","title":{"rendered":"Kho\u1ea3ng c\u00e1ch ph\u1ee9c t\u1ea1p \u1ea9n gi\u1ea5u: Khi c\u00e1c k\u1ef9 s\u01b0 c\u1ea5p d\u01b0\u1edbi x\u00e2y d\u1ef1ng sai s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3"},"content":{"rendered":"

M\u00f4 h\u00ecnh h\u00f3a d\u1eef li\u1ec7u th\u01b0\u1eddng l\u00e0 n\u1ec1n t\u1ea3ng v\u00f4 h\u00ecnh c\u1ee7a b\u1ea5t k\u1ef3 \u1ee9ng d\u1ee5ng ph\u1ea7n m\u1ec1m n\u00e0o. Trong khi m\u00e3 ngu\u1ed3n th\u1ef1c thi logic kinh doanh \u0111\u01b0\u1ee3c ch\u00fa \u00fd nhi\u1ec1u, th\u00ec l\u01b0\u1ee3c \u0111\u1ed3 b\u00ean d\u01b0\u1edbi n\u00f3 quy\u1ebft \u0111\u1ecbnh hi\u1ec7u su\u1ea5t, kh\u1ea3 n\u0103ng m\u1edf r\u1ed9ng v\u00e0 kh\u1ea3 n\u0103ng b\u1ea3o tr\u00ec. \u0110\u1ed1i v\u1edbi nhi\u1ec1u k\u1ef9 s\u01b0 c\u1ea5p d\u01b0\u1edbi, s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 (ERD) l\u00e0 m\u1ed9t b\u00e0i t\u1eadp \u0111\u01a1n gi\u1ea3n g\u1ed3m vi\u1ec7c v\u1ebd c\u00e1c h\u00ecnh h\u1ed9p v\u00e0 n\u1ed1i c\u00e1c \u0111\u01b0\u1eddng th\u1eb3ng. Tuy nhi\u00ean, s\u1ef1 \u0111\u01a1n gi\u1ea3n n\u00e0y l\u00e0 sai l\u1ea7m. M\u1ed9t s\u01a1 \u0111\u1ed3 ERD \u0111\u01b0\u1ee3c x\u00e2y d\u1ef1ng k\u00e9m s\u1ebd t\u1ea1o ra n\u1ee3 k\u1ef9 thu\u1eadt ng\u00e0y c\u00e0ng gia t\u0103ng theo th\u1eddi gian, d\u1eabn \u0111\u1ebfn c\u00e1c truy v\u1ea5n ph\u1ee9c t\u1ea1p, v\u1ea5n \u0111\u1ec1 v\u1ec1 t\u00ednh to\u00e0n v\u1eb9n d\u1eef li\u1ec7u v\u00e0 c\u00e1c thao t\u00e1c di chuy\u1ec3n d\u1eef li\u1ec7u kh\u00f3 kh\u0103n.<\/p>\n

H\u01b0\u1edbng d\u1eabn n\u00e0y kh\u00e1m ph\u00e1 kho\u1ea3ng c\u00e1ch ph\u1ee9c t\u1ea1p \u1ea9n gi\u1ea5u. N\u00f3 x\u00e1c \u0111\u1ecbnh n\u01a1i x\u1ea3y ra s\u1ef1 thi\u1ebfu k\u1ebft n\u1ed1i gi\u1eefa ki\u1ebfn th\u1ee9c l\u00fd thuy\u1ebft v\u00e0 \u1ee9ng d\u1ee5ng th\u1ef1c ti\u1ec5n. B\u1eb1ng c\u00e1ch hi\u1ec3u r\u00f5 nh\u1eefng sai l\u1ea7m n\u00e0y, c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n c\u00f3 th\u1ec3 v\u01b0\u1ee3t qua vi\u1ec7c v\u1ebd s\u01a1 \u0111\u1ed3 c\u01a1 b\u1ea3n \u0111\u1ec3 ti\u1ebfn t\u1edbi t\u01b0 duy ki\u1ebfn tr\u00fac th\u1ef1c s\u1ef1.<\/p>\n

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

1. Hi\u1ec3u r\u00f5 n\u1ec1n t\u1ea3ng c\u1ee7a m\u00f4 h\u00ecnh h\u00f3a d\u1eef li\u1ec7u \ud83c\udfd7\ufe0f<\/h2>\n

Tr\u01b0\u1edbc khi \u0111i v\u00e0o c\u00e1c l\u1ed7i, \u0111i\u1ec1u quan tr\u1ecdng l\u00e0 ph\u1ea3i x\u00e1c \u0111\u1ecbnh r\u00f5 ERD th\u1ef1c s\u1ef1 \u0111\u1ea1i di\u1ec7n cho \u0111i\u1ec1u g\u00ec. N\u00f3 kh\u00f4ng ch\u1ec9 \u0111\u01a1n thu\u1ea7n l\u00e0 m\u1ed9t b\u1ea3n v\u1ebd; m\u00e0 l\u00e0 m\u1ed9t h\u1ee3p \u0111\u1ed3ng gi\u1eefa \u1ee9ng d\u1ee5ng v\u00e0 l\u1edbp l\u01b0u tr\u1eef. ERD tr\u1ef1c quan h\u00f3a c\u00e1c th\u1ef1c th\u1ec3 (b\u1ea3ng), thu\u1ed9c t\u00ednh (c\u1ed9t) v\u00e0 m\u1ed1i quan h\u1ec7 (kh\u00f3a ngo\u1ea1i).<\/p>\n

Khi m\u1ed9t k\u1ef9 s\u01b0 coi \u0111\u00e2y l\u00e0 m\u1ed9t t\u00e0i s\u1ea3n t\u0129nh \u0111\u01b0\u1ee3c t\u1ea1o ra m\u1ed9t l\u1ea7n r\u1ed3i b\u1ecf qu\u00ean, h\u1ecd s\u1ebd b\u1ecf l\u1ee1 b\u1ea3n ch\u1ea5t \u0111\u1ed9ng c\u1ee7a d\u1eef li\u1ec7u. C\u00e1c m\u00f4 h\u00ecnh d\u1eef li\u1ec7u thay \u0111\u1ed5i theo s\u1ef1 thay \u0111\u1ed5i y\u00eau c\u1ea7u kinh doanh. M\u1ed9t k\u1ef9 s\u01b0 c\u1ea5p d\u01b0\u1edbi c\u00f3 th\u1ec3 ch\u1ec9 t\u1eadp trung v\u00e0o t\u00ednh n\u0103ng ngay l\u1eadp t\u1ee9c, ch\u1eb3ng h\u1ea1n nh\u01b0 l\u01b0u t\u00ean ng\u01b0\u1eddi d\u00f9ng, trong khi b\u1ecf qua c\u00e1ch ng\u01b0\u1eddi d\u00f9ng \u0111\u00f3 t\u01b0\u01a1ng t\u00e1c v\u1edbi c\u00e1c th\u1ef1c th\u1ec3 kh\u00e1c nh\u01b0 \u0111\u01a1n h\u00e0ng, \u0111\u0103ng k\u00fd ho\u1eb7c nh\u1eadt k\u00fd.<\/p>\n

    \n
  • Th\u1ef1c th\u1ec3:<\/strong> Ch\u00fang \u0111\u1ea1i di\u1ec7n cho c\u00e1c \u0111\u1ed1i t\u01b0\u1ee3ng ho\u1eb7c kh\u00e1i ni\u1ec7m trong th\u1ebf gi\u1edbi th\u1ef1c (v\u00ed d\u1ee5: Kh\u00e1ch h\u00e0ng, S\u1ea3n ph\u1ea9m, H\u00f3a \u0111\u01a1n).<\/li>\n
  • Thu\u1ed9c t\u00ednh:<\/strong> Ch\u00fang l\u00e0 c\u00e1c thu\u1ed9c t\u00ednh \u0111\u1ecbnh ngh\u0129a th\u1ef1c th\u1ec3 (v\u00ed d\u1ee5: Email, Gi\u00e1, Ng\u00e0y).<\/li>\n
  • M\u1ed1i quan h\u1ec7:<\/strong> Ch\u00fang x\u00e1c \u0111\u1ecbnh c\u00e1ch c\u00e1c th\u1ef1c th\u1ec3 t\u01b0\u01a1ng t\u00e1c v\u1edbi nhau (v\u00ed d\u1ee5: M\u1ed9t-nhi\u1ec1u, Nhi\u1ec1u-nhi\u1ec1u).<\/li>\n<\/ul>\n

    M\u1ed9t m\u00f4 h\u00ecnh v\u1eefng ch\u1eafc c\u1ea7n t\u00ednh \u0111\u1ebfn s\u1ef1 ph\u00e1t tri\u1ec3n trong t\u01b0\u01a1ng lai. N\u00f3 d\u1ef1 \u0111o\u00e1n c\u00e1ch m\u1ed9t ‘Kh\u00e1ch h\u00e0ng’ c\u00f3 th\u1ec3 tr\u1edf th\u00e0nh ‘Ng\u01b0\u1eddi d\u00f9ng’ ho\u1eb7c c\u00e1ch m\u1ed9t ‘S\u1ea3n ph\u1ea9m’ c\u00f3 th\u1ec3 c\u1ea7n c\u00e1c bi\u1ebfn th\u1ec3. S\u01a1 \u0111\u1ed3 ban \u0111\u1ea7u c\u1ea7n \u0111\u1ee7 linh ho\u1ea1t \u0111\u1ec3 ch\u1ea5p nh\u1eadn nh\u1eefng thay \u0111\u1ed5i n\u00e0y m\u00e0 kh\u00f4ng c\u1ea7n ph\u1ea3i x\u00e2y d\u1ef1ng l\u1ea1i ho\u00e0n to\u00e0n.<\/p>\n

    2. B\u1eaby c\u1ea5p \u0111\u1ed9: Hi\u1ec3u sai m\u1ed1i quan h\u1ec7 \ud83d\udd04<\/h2>\n

    C\u1ea5p \u0111\u1ed9 (Cardinality) l\u00e0 ngu\u1ed3n g\u1ed1c ph\u1ed5 bi\u1ebfn nh\u1ea5t c\u1ee7a s\u1ef1 th\u1ea5t b\u1ea1i v\u1ec1 c\u1ea5u tr\u00fac trong thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u. N\u00f3 x\u00e1c \u0111\u1ecbnh m\u1ed1i quan h\u1ec7 s\u1ed1 l\u01b0\u1ee3ng gi\u1eefa c\u00e1c th\u1ec3 hi\u1ec7n c\u1ee7a c\u00e1c th\u1ef1c th\u1ec3. Vi\u1ec7c hi\u1ec3u sai \u0111i\u1ec1u n\u00e0y d\u1eabn \u0111\u1ebfn l\u01b0u tr\u1eef k\u00e9m hi\u1ec7u qu\u1ea3 v\u00e0 logic k\u1ebft n\u1ed1i ph\u1ee9c t\u1ea1p.<\/p>\n

    C\u00e1c t\u00ecnh hu\u1ed1ng c\u1ea5p \u0111\u1ed9 ph\u1ed5 bi\u1ebfn<\/h3>\n

    C\u00e1c k\u1ef9 s\u01b0 th\u01b0\u1eddng m\u1eb7c \u0111\u1ecbnh v\u00e0o m\u1ed1i quan h\u1ec7 r\u00f5 r\u00e0ng nh\u1ea5t m\u00e0 kh\u00f4ng c\u00e2n nh\u1eafc c\u00e1c tr\u01b0\u1eddng h\u1ee3p bi\u00ean. H\u00e3y xem x\u00e9t c\u00e1c t\u00ecnh hu\u1ed1ng sau \u0111\u00e2y, n\u01a1i c\u00e1c gi\u1ea3 \u0111\u1ecbnh d\u1eabn \u0111\u1ebfn sai s\u00f3t:<\/p>\n

      \n
    • M\u1ed9t-nh\u1ea5t (1:1):<\/strong>Th\u01b0\u1eddng b\u1ecb l\u1ea1m d\u1ee5ng. N\u1ebfu hai th\u1ef1c th\u1ec3 c\u00f3 m\u1ed1i quan h\u1ec7 1:1, ch\u00fang th\u01b0\u1eddng n\u00ean \u0111\u01b0\u1ee3c g\u1ed9p th\u00e0nh m\u1ed9t b\u1ea3ng duy nh\u1ea5t \u0111\u1ec3 gi\u1ea3m chi ph\u00ed k\u1ebft n\u1ed1i, tr\u1eeb khi y\u00eau c\u1ea7u t\u00e1ch bi\u1ec7t b\u1ea3o m\u1eadt nghi\u00eam ng\u1eb7t.<\/li>\n
    • M\u1ed9t-nhi\u1ec1u (1:N):<\/strong>M\u1ed1i quan h\u1ec7 ph\u1ed5 bi\u1ebfn nh\u1ea5t. M\u1ed9t b\u1ea3n ghi Cha li\u00ean k\u1ebft v\u1edbi nhi\u1ec1u b\u1ea3n ghi Con. Kh\u00f3a ngo\u1ea1i ph\u1ea3i n\u1eb1m \u1edf ph\u00eda Con.<\/li>\n
    • Nhi\u1ec1u-nhi\u1ec1u (M:N):<\/strong>\u0110\u00e2y ch\u00ednh l\u00e0 n\u01a1i kho\u1ea3ng c\u00e1ch ph\u1ee9c t\u1ea1p m\u1edf r\u1ed9ng ra. M\u1ed1i quan h\u1ec7 M:N tr\u1ef1c ti\u1ebfp l\u00e0 kh\u00f4ng th\u1ec3 v\u1ec1 m\u1eb7t v\u1eadt l\u00fd trong m\u00f4 h\u00ecnh quan h\u1ec7 m\u00e0 kh\u00f4ng c\u00f3 m\u1ed9t b\u1ea3ng trung gian.<\/li>\n<\/ul>\n

      B\u1ea3ng: L\u1ed7i tri\u1ec3n khai c\u1ea5p \u0111\u1ed9<\/h3>\n\n\n\n\n\n\n\n
      T\u00ecnh hu\u1ed1ng<\/th>\nC\u00e1ch ti\u1ebfp c\u1eadn sai<\/th>\nC\u00e1ch ti\u1ebfp c\u1eadn \u0111\u00fang<\/th>\n<\/tr>\n<\/thead>\n
      Sinh vi\u00ean v\u00e0 Kh\u00f3a h\u1ecdc<\/td>\nTh\u00eam c\u1ed9t “CourseID” v\u00e0o b\u1ea3ng “Sinh vi\u00ean”<\/td>\nT\u1ea1o b\u1ea3ng li\u00ean k\u1ebft “Student_Course”<\/td>\n<\/tr>\n
      \u0110\u01a1n h\u00e0ng v\u00e0 s\u1ea3n ph\u1ea9m<\/td>\nCh\u00e8n chi ti\u1ebft s\u1ea3n ph\u1ea9m tr\u1ef1c ti\u1ebfp v\u00e0o b\u1ea3ng \u0110\u01a1n h\u00e0ng<\/td>\nLi\u00ean k\u1ebft th\u00f4ng qua b\u1ea3ng OrderItems<\/td>\n<\/tr>\n
      Nh\u00e2n vi\u00ean v\u00e0 ph\u00f2ng ban<\/td>\nCho ph\u00e9p m\u1ed9t nh\u00e2n vi\u00ean thu\u1ed9c v\u1ec1 nhi\u1ec1u ph\u00f2ng ban m\u00e0 kh\u00f4ng c\u1ea7n b\u1ea3ng li\u00ean k\u1ebft<\/td>\nT\u00e1ch bi\u1ec7t m\u1ed1i quan h\u1ec7 \u00e1nh x\u1ea1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

      Khi c\u00e1c k\u1ef9 s\u01b0 c\u1ed1 g\u1eafng \u00e9p m\u1ed9t m\u1ed1i quan h\u1ec7 Nhi\u1ec1u-\u0111\u1ebfn-Nhi\u1ec1u v\u00e0o m\u1ed9t b\u1ea3ng duy nh\u1ea5t b\u1eb1ng c\u00e1ch l\u1eb7p l\u1ea1i d\u1eef li\u1ec7u, h\u1ecd s\u1ebd t\u1ea1o ra s\u1ef1 tr\u00f9ng l\u1eb7p. N\u1ebfu gi\u00e1 s\u1ea3n ph\u1ea9m thay \u0111\u1ed5i, n\u00f3 ph\u1ea3i \u0111\u01b0\u1ee3c c\u1eadp nh\u1eadt trong m\u1ecdi b\u1ea3n ghi \u0111\u01a1n h\u00e0ng m\u00e0 s\u1ea3n ph\u1ea9m \u0111\u00f3 xu\u1ea5t hi\u1ec7n. \u0110i\u1ec1u n\u00e0y vi ph\u1ea1m c\u00e1c nguy\u00ean t\u1eafc chu\u1ea9n h\u00f3a v\u00e0 t\u1ea1o ra nh\u1eefng r\u1eafc r\u1ed1i trong b\u1ea3o tr\u00ec.<\/p>\n

      3. Nh\u1eefng hi\u1ec3u l\u1ea7m v\u1ec1 chu\u1ea9n h\u00f3a v\u00e0 c\u00e1c ki\u1ec3m tra th\u1ef1c t\u1ebf \ud83d\udcc9<\/h2>\n

      Chu\u1ea9n h\u00f3a l\u00e0 m\u1ed9t kh\u00e1i ni\u1ec7m ti\u00eau chu\u1ea9n \u0111\u01b0\u1ee3c gi\u1ea3ng d\u1ea1y trong m\u00f4i tr\u01b0\u1eddng h\u1ecdc thu\u1eadt. M\u1ee5c ti\u00eau l\u00e0 gi\u1ea3m thi\u1ec3u s\u1ef1 tr\u00f9ng l\u1eb7p d\u1eef li\u1ec7u v\u00e0 c\u1ea3i thi\u1ec7n t\u00ednh to\u00e0n v\u1eb9n. Tuy nhi\u00ean, c\u00e1c k\u1ef9 s\u01b0 tr\u1ebb th\u01b0\u1eddng chu\u1ea9n h\u00f3a \u0111\u1ebfn m\u1ee9c c\u1ef1c \u0111oan (\u0111\u1ebfn 5NF) m\u00e0 kh\u00f4ng c\u00e2n nh\u1eafc \u0111\u1ebfn c\u00e1c th\u1ecfa thu\u1eadn v\u1ec1 hi\u1ec7u su\u1ea5t.<\/p>\n

      V\u0169ng l\u1ea7y c\u1ee7a vi\u1ec7c chu\u1ea9n h\u00f3a qu\u00e1 m\u1ee9c<\/h3>\n

      M\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 chu\u1ea9n h\u00f3a qu\u00e1 m\u1ee9c chia d\u1eef li\u1ec7u th\u00e0nh qu\u00e1 nhi\u1ec1u b\u1ea3ng. D\u00f9 \u0111i\u1ec1u n\u00e0y \u0111\u1ea3m b\u1ea3o t\u00ednh nh\u1ea5t qu\u00e1n, nh\u01b0ng l\u1ea1i bu\u1ed9c \u1ee9ng d\u1ee5ng ph\u1ea3i th\u1ef1c hi\u1ec7n qu\u00e1 nhi\u1ec1u thao t\u00e1c n\u1ed1i (join). M\u1ed7i thao t\u00e1c n\u1ed1i \u0111\u1ec1u l\u00e0m t\u0103ng chi ph\u00ed t\u00ednh to\u00e1n. Trong c\u00e1c h\u1ec7 th\u1ed1ng c\u00f3 l\u01b0u l\u01b0\u1ee3ng cao, \u0111i\u1ec1u n\u00e0y c\u00f3 th\u1ec3 tr\u1edf th\u00e0nh \u0111i\u1ec3m ngh\u1ebdn.<\/p>\n

        \n
      • 1NF (D\u1ea1ng chu\u1ea9n th\u1ee9 nh\u1ea5t):<\/strong>Gi\u00e1 tr\u1ecb nguy\u00ean t\u1eed. Kh\u00f4ng c\u00f3 danh s\u00e1ch trong m\u1ed9t \u00f4 duy nh\u1ea5t.<\/li>\n
      • 2NF (D\u1ea1ng chu\u1ea9n th\u1ee9 hai):<\/strong>Kh\u00f4ng c\u00f3 ph\u1ee5 thu\u1ed9c ri\u00eang ph\u1ea7n. T\u1ea5t c\u1ea3 c\u00e1c thu\u1ed9c t\u00ednh kh\u00f4ng kh\u00f3a ph\u1ea3i ph\u1ee5 thu\u1ed9c v\u00e0o to\u00e0n b\u1ed9 kh\u00f3a ch\u00ednh.<\/li>\n
      • 3NF (D\u1ea1ng chu\u1ea9n th\u1ee9 ba):<\/strong>Kh\u00f4ng c\u00f3 ph\u1ee5 thu\u1ed9c b\u1eafc c\u1ea7u. C\u00e1c thu\u1ed9c t\u00ednh kh\u00f4ng \u0111\u01b0\u1ee3c ph\u1ee5 thu\u1ed9c v\u00e0o c\u00e1c thu\u1ed9c t\u00ednh kh\u00f4ng kh\u00f3a kh\u00e1c.<\/li>\n<\/ul>\n

        M\u1ed9t sai l\u1ea7m ph\u1ed5 bi\u1ebfn l\u00e0 cho r\u1eb1ng 3NF lu\u00f4n l\u00e0 m\u1ee5c ti\u00eau. Trong m\u1ed9t s\u1ed1 tr\u01b0\u1eddng h\u1ee3p, vi\u1ec7c kh\u00f4ng chu\u1ea9n h\u00f3a l\u00e0 m\u1ed9t l\u1ef1a ch\u1ecdn thi\u1ebft k\u1ebf c\u00f3 ch\u1ee7 \u00fd. V\u00ed d\u1ee5, l\u01b0u tr\u1eef \u201cT\u1ed5ng s\u1ed1 ti\u1ec1n \u0111\u01a1n h\u00e0ng\u201d tr\u1ef1c ti\u1ebfp tr\u00ean b\u1ea3ng \u0110\u01a1n h\u00e0ng gi\u00fap tr\u00e1nh vi\u1ec7c t\u00ednh t\u1ed5ng c\u00e1c m\u1ee5c m\u1ed7i khi hi\u1ec3n th\u1ecb \u0111\u01a1n h\u00e0ng. \u0110i\u1ec1u n\u00e0y \u0111\u1ed5i l\u1ea5y hi\u1ec7u su\u1ea5t ghi cho hi\u1ec7u su\u1ea5t \u0111\u1ecdc.<\/p>\n

        B\u1ea3ng: Chu\u1ea9n h\u00f3a so v\u1edbi kh\u00f4ng chu\u1ea9n h\u00f3a<\/h3>\n\n\n\n\n\n\n\n\n
        Y\u1ebfu t\u1ed1<\/th>\nChu\u1ea9n h\u00f3a (3NF)<\/th>\nKh\u00f4ng chu\u1ea9n h\u00f3a<\/th>\n<\/tr>\n<\/thead>\n
        S\u1ef1 tr\u00f9ng l\u1eb7p d\u1eef li\u1ec7u<\/td>\nTh\u1ea5p<\/td>\nCao<\/td>\n<\/tr>\n
        T\u1ed1c \u0111\u1ed9 ghi<\/td>\nNhanh<\/td>\nCh\u1eadm h\u01a1n<\/td>\n<\/tr>\n
        T\u1ed1c \u0111\u1ed9 \u0111\u1ecdc<\/td>\nCh\u1eadm h\u01a1n (Nhi\u1ec1u thao t\u00e1c n\u1ed1i h\u01a1n)<\/td>\nNhanh<\/td>\n<\/tr>\n
        \u0110\u1ed9 to\u00e0n v\u1eb9n d\u1eef li\u1ec7u<\/td>\nCao<\/td>\nTh\u1ea5p h\u01a1n (Y\u00eau c\u1ea7u logic)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

        Quy\u1ebft \u0111\u1ecbnh lo\u1ea1i b\u1ecf chu\u1ea9n h\u00f3a ph\u1ea3i d\u1ef1a tr\u00ean d\u1eef li\u1ec7u. N\u00f3 kh\u00f4ng n\u00ean x\u1ea3y ra m\u1ed9t c\u00e1ch t\u00f9y ti\u1ec7n. C\u00e1c k\u1ef9 s\u01b0 c\u1ea7n ph\u00e2n t\u00edch hi\u1ec7u su\u1ea5t truy v\u1ea5n tr\u01b0\u1edbc khi h\u1ee3p nh\u1ea5t c\u00e1c b\u1ea3ng. Tu\u00e2n theo quy t\u1eafc chu\u1ea9n h\u00f3a m\u1ed9t c\u00e1ch m\u00f9 qu\u00e1ng m\u00e0 kh\u00f4ng c\u00f3 b\u1ed1i c\u1ea3nh s\u1ebd d\u1eabn \u0111\u1ebfn c\u00e1c h\u1ec7 th\u1ed1ng nh\u1ea5t qu\u00e1n nh\u01b0ng ch\u1eadm ch\u1ea1p.<\/p>\n

        4. Quy \u01b0\u1edbc \u0111\u1eb7t t\u00ean v\u00e0 \u0111\u1ed9 r\u00f5 ngh\u0129a \ud83c\udff7\ufe0f<\/h2>\n

        T\u00ean l\u01b0\u1ee3c \u0111\u1ed3 l\u00e0 t\u1eeb v\u1ef1ng c\u1ee7a c\u01a1 s\u1edf d\u1eef li\u1ec7u. N\u1ebfu t\u1eeb v\u1ef1ng m\u01a1 h\u1ed3, h\u1ec7 th\u1ed1ng s\u1ebd tr\u1edf n\u00ean kh\u00f3 hi\u1ec3u \u0111\u1ed1i v\u1edbi c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n t\u01b0\u01a1ng lai. \u0110\u00e2y l\u00e0 m\u1ed9t v\u1ea5n \u0111\u1ec1 ph\u1ed5 bi\u1ebfn khi s\u1ef1 ch\u00ednh x\u00e1c k\u1ef9 thu\u1eadt b\u1ecb hy sinh \u0111\u1ec3 ti\u1ebft ki\u1ec7m ch\u1eef.<\/p>\n

        M\u1ed9t tr\u01b0\u1eddng \u0111\u01b0\u1ee3c \u0111\u1eb7t t\u00ean l\u00e0 tr\u1ea1ng th\u00e1i<\/code> l\u00e0 nguy hi\u1ec3m. N\u00f3 c\u00f3 ngh\u0129a l\u00e0 g\u00ec? C\u00f3 ph\u1ea3i l\u00e0 t\u00e0i kho\u1ea3n \u0111ang ho\u1ea1t \u0111\u1ed9ng? M\u1ed9t kho\u1ea3n thanh to\u00e1n \u0111ang ch\u1edd x\u1eed l\u00fd? M\u1ed9t b\u1ea3n ghi \u0111\u00e3 b\u1ecb x\u00f3a? Kh\u00f4ng c\u00f3 b\u1ed1i c\u1ea3nh, \u00fd ngh\u0129a s\u1ebd b\u1ecb m\u1ea5t. T\u01b0\u01a1ng t\u1ef1, vi\u1ec7c s\u1eed d\u1ee5ng t\u00ean s\u1ed1 nhi\u1ec1u cho c\u00e1c b\u1ea3ng (v\u00ed d\u1ee5 nh\u01b0 Ng\u01b0\u1eddi d\u00f9ng<\/code>) thay v\u00ec s\u1ed1 \u00edt (v\u00ed d\u1ee5 nh\u01b0 Ng\u01b0\u1eddi d\u00f9ng<\/code>) s\u1ebd t\u1ea1o ra s\u1ef1 kh\u00f4ng nh\u1ea5t qu\u00e1n.<\/p>\n

          \n
        • Nh\u1ea5t qu\u00e1n:<\/strong> N\u1ebfu m\u1ed9t b\u1ea3ng s\u1eed d\u1ee5ng snake_case<\/code>, t\u1ea5t c\u1ea3 \u0111\u1ec1u ph\u1ea3i s\u1eed d\u1ee5ng snake_case<\/code>.<\/li>\n
        • M\u00f4 t\u1ea3 r\u00f5 r\u00e0ng:<\/strong> S\u1eed d\u1ee5ng t\u00ean m\u00f4 t\u1ea3 d\u1eef li\u1ec7u, ch\u1ee9 kh\u00f4ng ch\u1ec9 \u0111\u1ecbnh d\u1ea1ng. Tr\u00e1nh c\u00e1c thu\u1eadt ng\u1eef chung nh\u01b0 b\u1ea3ng1<\/code> ho\u1eb7c d\u1eef li\u1ec7u<\/code>.<\/li>\n
        • B\u1ed1i c\u1ea3nh:<\/strong> Bao g\u1ed3m t\u00ean th\u1ef1c th\u1ec3 trong kh\u00f3a quan h\u1ec7 n\u1ebfu c\u00f3 s\u1ef1 m\u01a1 h\u1ed3. S\u1eed d\u1ee5ng user_id<\/code> thay v\u00ec ch\u1ec9 id<\/code> khi c\u00f3 th\u1ec3.<\/li>\n<\/ul>\n

          X\u00e9t t\u00ecnh hu\u1ed1ng c\u1ee7a m\u1ed9t h\u1ec7 th\u1ed1ng c\u00f3 nhi\u1ec1u lo\u1ea1i ng\u01b0\u1eddi d\u00f9ng: Qu\u1ea3n tr\u1ecb vi\u00ean, Kh\u00e1ch h\u00e0ng v\u00e0 Nh\u00e0 cung c\u1ea5p. M\u1ed9t b\u1ea3ng duy nh\u1ea5t c\u00f3 t\u00ean l\u00e0Ng\u01b0\u1eddi d\u00f9ng<\/code> c\u00f3 th\u1ec3 ch\u1ee9a m\u1ed9t c\u1ed9tvai tr\u00f2<\/code> c\u1ed9t. \u0110\u00e2y l\u00e0 m\u1ed9t ‘b\u1ea3ng Ch\u00faa’. M\u1ed9t c\u00e1ch ti\u1ebfp c\u1eadn t\u1ed1t h\u01a1n l\u00e0 s\u1eed d\u1ee5ng c\u00e1c b\u1ea3ng ri\u00eang bi\u1ec7t ho\u1eb7c chi\u1ebfn l\u01b0\u1ee3c k\u1ebf th\u1eeba r\u00f5 r\u00e0ng. S\u1ef1 ph\u00e2n bi\u1ec7t n\u00e0y tr\u1edf n\u00ean quan tr\u1ecdng khi quy\u1ec1n h\u1ea1n v\u00e0 quy t\u1eafc truy c\u1eadp d\u1eef li\u1ec7u kh\u00e1c bi\u1ec7t \u0111\u00e1ng k\u1ec3 gi\u1eefa c\u00e1c vai tr\u00f2.<\/p>\n

          5. B\u1ecf qua logic kinh doanh trong thi\u1ebft k\u1ebf k\u1ef9 thu\u1eadt \ud83e\udde0<\/h2>\n

          Kho\u1ea3ng c\u00e1ch l\u1edbn nh\u1ea5t gi\u1eefa k\u1ef9 s\u01b0 c\u1ea5p th\u1ea5p v\u00e0 c\u1ea5p cao l\u00e0 s\u1ef1 hi\u1ec3u bi\u1ebft v\u1ec1 logic kinh doanh. M\u1ed9t k\u1ef9 s\u01b0 c\u1ea5p th\u1ea5p c\u00f3 th\u1ec3 x\u00e2y d\u1ef1ng m\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 ph\u00f9 h\u1ee3p ho\u00e0n h\u1ea3o v\u1edbi y\u00eau c\u1ea7u m\u00e3 hi\u1ec7n t\u1ea1i nh\u01b0ng s\u1ebd th\u1ea5t b\u1ea1i khi quy t\u1eafc kinh doanh thay \u0111\u1ed5i.<\/p>\n

          Sai l\u1ea7m v\u1ec1 thao t\u00e1c x\u00f3a m\u1ec1m<\/h3>\n

          Nhi\u1ec1u nh\u00e0 ph\u00e1t tri\u1ec3n \u0111\u01a1n gi\u1ea3n th\u00eam m\u1ed9t c\u1ed9tdeleted_at<\/code> v\u00e0o m\u1ed9t b\u1ea3ng. \u0110i\u1ec1u n\u00e0y ho\u1ea1t \u0111\u1ed9ng t\u1ed1t v\u1edbi c\u00e1c tr\u01b0\u1eddng h\u1ee3p \u0111\u01a1n gi\u1ea3n. Tuy nhi\u00ean, n\u1ebfu m\u1ed9t ng\u01b0\u1eddi d\u00f9ng b\u1ecb x\u00f3a, c\u00e1c nh\u1eadt k\u00fd li\u00ean quan \u0111\u1ebfn h\u1ecd c\u00f3 n\u00ean b\u1ecb x\u00f3a kh\u00f4ng? C\u00e1c h\u1ed3 s\u01a1 t\u00e0i ch\u00ednh c\u1ee7a h\u1ecd c\u00f3 n\u00ean \u0111\u01b0\u1ee3c gi\u1eef l\u1ea1i \u0111\u1ec3 tu\u00e2n th\u1ee7 ki\u1ec3m to\u00e1n? L\u01b0\u1ee3c \u0111\u1ed3 ERD n\u00ean ph\u1ea3n \u00e1nh nh\u1eefng r\u00e0ng bu\u1ed9c n\u00e0y th\u00f4ng qua c\u00e1c r\u00e0ng bu\u1ed9c v\u00e0 tr\u00ecnh k\u00edch ho\u1ea1t, ch\u1ee9 kh\u00f4ng ch\u1ec9 d\u1ef1a v\u00e0o m\u00e3 \u1ee9ng d\u1ee5ng.<\/p>\n

          V\u1ea5n \u0111\u1ec1 NULL<\/h3>\n

          Cho ph\u00e9p gi\u00e1 tr\u1ecb NULL th\u01b0\u1eddng l\u00e0 ngu\u1ed3n g\u1ed1c c\u1ee7a s\u1ef1 ph\u1ee9c t\u1ea1p \u1ea9n. Trong m\u1ed9t s\u1ed1 tr\u01b0\u1eddng h\u1ee3p, NULL mang \u00fd ngh\u0129a kh\u00e1c bi\u1ec7t v\u1ec1 m\u1eb7t ng\u1eef ngh\u0129a so v\u1edbi chu\u1ed7i r\u1ed7ng ho\u1eb7c s\u1ed1 0. N\u1ebfu m\u1ed9t tr\u01b0\u1eddng l\u00e0 t\u00f9y ch\u1ecdn, l\u01b0\u1ee3c \u0111\u1ed3 ERD n\u00ean ch\u1ec9 r\u00f5 \u0111i\u1ec1u n\u00e0y. Tuy nhi\u00ean, vi\u1ec7c d\u1ef1a v\u00e0o NULL \u0111\u1ec3 ki\u1ec3m so\u00e1t logic b\u1ecb khuy\u1ebfn c\u00e1o kh\u00f4ng n\u00ean l\u00e0m.<\/p>\n

            \n
          • T\u00ednh to\u00e0n v\u1eb9n tham chi\u1ebfu:<\/strong> Kh\u00f3a ngo\u1ea1i n\u00ean tr\u00e1nh NULL tr\u1eeb khi m\u1ed1i quan h\u1ec7 th\u1ef1c s\u1ef1 l\u00e0 t\u00f9y ch\u1ecdn.<\/li>\n
          • T\u00ednh to\u00e1n:<\/strong> C\u00e1c gi\u00e1 tr\u1ecb NULL lan truy\u1ec1n qua c\u00e1c ph\u00e9p t\u00ednh, d\u1eabn \u0111\u1ebfn k\u1ebft qu\u1ea3 l\u00e0 NULL. \u0110i\u1ec1u n\u00e0y c\u00f3 th\u1ec3 l\u00e0m h\u1ecfng c\u00e1c truy v\u1ea5n t\u1ed5ng h\u1ee3p.<\/li>\n
          • Ch\u1ec9 m\u1ee5c:<\/strong> C\u00e1ch x\u1eed l\u00fd NULL trong ch\u1ec9 m\u1ee5c kh\u00e1c nhau t\u00f9y theo h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u, c\u00f3 th\u1ec3 \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn hi\u1ec7u su\u1ea5t truy v\u1ea5n.<\/li>\n<\/ul>\n

            6. G\u00e1nh n\u1eb7ng b\u1ea3o tr\u00ec do thi\u1ebft k\u1ebf k\u00e9m \ud83d\udd27<\/h2>\n

            N\u1ee3 k\u1ef9 thu\u1eadt kh\u00f4ng ch\u1ec9 l\u00e0 v\u1ec1 m\u00e3 ch\u1eadm; \u0111\u00f3 l\u00e0 v\u1ec1 s\u1ef1 c\u1ee9ng nh\u1eafc v\u1ec1 c\u1ea5u tr\u00fac. M\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 ERD \u0111\u01b0\u1ee3c thi\u1ebft k\u1ebf k\u00e9m s\u1ebd khi\u1ebfn vi\u1ec7c thay \u0111\u1ed5i tr\u1edf n\u00ean \u0111au \u0111\u1edbn. Khi m\u1ed9t y\u00eau c\u1ea7u m\u1edbi xu\u1ea5t hi\u1ec7n, ch\u1eb3ng h\u1ea1n nh\u01b0 th\u00eam m\u1ed9t ‘\u0110\u1ecba ch\u1ec9 h\u00f3a \u0111\u01a1n’ ri\u00eang bi\u1ec7t v\u1edbi ‘\u0110\u1ecba ch\u1ec9 giao h\u00e0ng’, k\u1ef9 s\u01b0 ph\u1ea3i \u0111\u00e1nh gi\u00e1 xem l\u01b0\u1ee3c \u0111\u1ed3 hi\u1ec7n t\u1ea1i c\u00f3 h\u1ed7 tr\u1ee3 \u0111i\u1ec1u n\u00e0y hay kh\u00f4ng.<\/p>\n

            \u00c1c m\u1ed9ng chuy\u1ec3n \u0111\u1ed5i<\/h3>\n

            Thay \u0111\u1ed5i l\u01b0\u1ee3c \u0111\u1ed3 c\u1ee7a c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ea3n xu\u1ea5t c\u00f3 h\u00e0ng tri\u1ec7u b\u1ea3n ghi \u0111\u00f2i h\u1ecfi l\u00ean k\u1ebf ho\u1ea1ch c\u1ea9n tr\u1ecdng. N\u1ebfu l\u01b0\u1ee3c \u0111\u1ed3 ERD kh\u00f4ng \u0111\u01b0\u1ee3c thi\u1ebft k\u1ebf v\u1edbi t\u00ednh to\u00e1n chuy\u1ec3n \u0111\u1ed5i, vi\u1ec7c thay \u0111\u1ed5i ki\u1ec3u c\u1ed9t ho\u1eb7c t\u00e1ch b\u1ea3ng c\u00f3 th\u1ec3 l\u00e0m kh\u00f3a h\u1ec7 th\u1ed1ng trong nhi\u1ec1u gi\u1edd. Th\u1eddi gian ng\u1eebng ho\u1ea1t \u0111\u1ed9ng n\u00e0y \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn doanh thu v\u00e0 ni\u1ec1m tin c\u1ee7a ng\u01b0\u1eddi d\u00f9ng.<\/p>\n

            C\u00e1c chi\u1ebfn l\u01b0\u1ee3c \u0111\u1ec3 gi\u1ea3m thi\u1ec3u \u0111i\u1ec1u n\u00e0y bao g\u1ed3m:<\/p>\n

              \n
            • Ki\u1ec3m so\u00e1t phi\u00ean b\u1ea3n cho l\u01b0\u1ee3c \u0111\u1ed3:<\/strong>Xem c\u1ea5u tr\u00fac c\u01a1 s\u1edf d\u1eef li\u1ec7u nh\u01b0 m\u00e3 \u1ee9ng d\u1ee5ng.<\/li>\n
            • T\u00ednh t\u01b0\u01a1ng th\u00edch ng\u01b0\u1ee3c:<\/strong>Th\u00eam c\u1ed9t tr\u01b0\u1edbc khi x\u00f3a ch\u00fang. Gi\u1eef l\u1ea1i c\u00e1c c\u1ed9t c\u0169 cho \u0111\u1ebfn khi qu\u00e1 tr\u00ecnh chuy\u1ec3n \u0111\u1ed5i ho\u00e0n t\u1ea5t.<\/li>\n
            • T\u00e0i li\u1ec7u:<\/strong>ERD ph\u1ea3i l\u00e0 ngu\u1ed3n th\u00f4ng tin \u0111\u00e1ng tin c\u1eady. N\u1ebfu n\u00f3 kh\u00f4ng kh\u1edbp v\u1edbi c\u01a1 s\u1edf d\u1eef li\u1ec7u, th\u00ec c\u01a1 s\u1edf d\u1eef li\u1ec7u l\u00e0 sai.<\/li>\n<\/ul>\n

              7. Danh s\u00e1ch ki\u1ec3m tra th\u1ef1c t\u1ebf cho vi\u1ec7c x\u00e1c minh ERD \u2705<\/h2>\n

              \u0110\u1ec3 \u0111\u1ea3m b\u1ea3o thi\u1ebft k\u1ebf v\u1eefng ch\u1eafc, c\u00e1c k\u1ef9 s\u01b0 n\u00ean \u0111i qua danh s\u00e1ch ki\u1ec3m tra x\u00e1c minh tr\u01b0\u1edbc khi ho\u00e0n thi\u1ec7n s\u01a1 \u0111\u1ed3. Quy tr\u00ecnh n\u00e0y gi\u00fap ph\u00e1t hi\u1ec7n c\u00e1c l\u1ed7i logic tr\u01b0\u1edbc khi tri\u1ec3n khai b\u1eaft \u0111\u1ea7u.<\/p>\n

              X\u00e1c minh tr\u01b0\u1edbc khi tri\u1ec3n khai<\/h3>\n\n\n\n\n\n\n\n\n\n
              Ki\u1ec3m tra<\/th>\nC\u00e2u h\u1ecfi<\/th>\nTi\u00eau ch\u00ed v\u01b0\u1ee3t qua<\/th>\n<\/tr>\n<\/thead>\n
              Kh\u00f3a ch\u00ednh<\/td>\nM\u1ed7i b\u1ea3ng c\u00f3 m\u1ed9t \u0111\u1ecbnh danh duy nh\u1ea5t kh\u00f4ng?<\/td>\nC\u00f3, t\u1ef1 t\u0103ng ho\u1eb7c UUID<\/td>\n<\/tr>\n
              Kh\u00f3a ngo\u1ea1i<\/td>\nC\u00e1c m\u1ed1i quan h\u1ec7 c\u00f3 \u0111\u01b0\u1ee3c x\u00e1c \u0111\u1ecbnh r\u00f5 r\u00e0ng kh\u00f4ng?<\/td>\nC\u00f3, v\u1edbi quy t\u1eafc ON DELETE\/UPDATE<\/td>\n<\/tr>\n
              D\u01b0 th\u1eeba<\/td>\nC\u00f3 d\u1eef li\u1ec7u n\u00e0o \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef \u1edf nhi\u1ec1u n\u01a1i kh\u00f4ng?<\/td>\nKh\u00f4ng, tr\u1eeb khi vi\u1ec7c lo\u1ea1i b\u1ecf chu\u1ea9n h\u00f3a l\u00e0 c\u00f3 ch\u1ee7 \u00fd<\/td>\n<\/tr>\n
              Kh\u1ea3 n\u0103ng m\u1edf r\u1ed9ng<\/td>\nC\u00f3 th\u1ec3 x\u1eed l\u00fd \u0111\u01b0\u1ee3c 10 l\u1ea7n dung l\u01b0\u1ee3ng d\u1eef li\u1ec7u hi\u1ec7n t\u1ea1i kh\u00f4ng?<\/td>\nCh\u1ec9 m\u1ee5c t\u1ed3n t\u1ea1i tr\u00ean c\u00e1c kh\u00f3a ngo\u1ea1i<\/td>\n<\/tr>\n
              Kh\u1ea3 n\u0103ng \u0111\u1ecdc hi\u1ec3u<\/td>\nNg\u01b0\u1eddi m\u1edbi v\u00e0o c\u00f3 th\u1ec3 hi\u1ec3u lu\u1ed3ng trong 5 ph\u00fat kh\u00f4ng?<\/td>\nQuy t\u1eafc \u0111\u1eb7t t\u00ean r\u00f5 r\u00e0ng<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

              8. C\u00f4ng c\u1ee5 so v\u1edbi Kh\u00e1i ni\u1ec7m \ud83d\udee0\ufe0f<\/h2>\n

              D\u1ec5 d\u00e0ng d\u1ef1a v\u00e0o c\u00e1c t\u00ednh n\u0103ng c\u1ee7a m\u1ed9t c\u00f4ng c\u1ee5 c\u1ee5 th\u1ec3 \u0111\u1ec3 gi\u1ea3i quy\u1ebft c\u00e1c v\u1ea5n \u0111\u1ec1 thi\u1ebft k\u1ebf. Tuy nhi\u00ean, c\u00f4ng c\u1ee5 ch\u1ec9 l\u00e0 th\u1ee9 y\u1ebfu so v\u1edbi kh\u00e1i ni\u1ec7m. D\u00f9 s\u1eed d\u1ee5ng c\u00f4ng c\u1ee5 m\u00f4 h\u00ecnh h\u00f3a tr\u1ef1c quan hay vi\u1ebft tr\u1ef1c ti\u1ebfp c\u00e1c t\u1eadp l\u1ec7nh SQL, logic n\u1ec1n t\u1ea3ng v\u1eabn nh\u01b0 nhau.<\/p>\n

              M\u1ed9t s\u1ed1 k\u1ef9 s\u01b0 t\u1ea1o ra c\u00e1c s\u01a1 \u0111\u1ed3 tr\u00f4ng ho\u00e0n h\u1ea3o v\u1ec1 m\u1eb7t tr\u1ef1c quan nh\u01b0ng l\u1ea1i kh\u00f4ng th\u1ec3 th\u1ef1c hi\u1ec7n \u0111\u01b0\u1ee3c v\u1ec1 m\u1eb7t ng\u1eef ph\u00e1p trong c\u01a1 s\u1edf d\u1eef li\u1ec7u m\u1ee5c ti\u00eau. V\u00ed d\u1ee5, m\u1ed9t s\u1ed1 c\u00f4ng c\u1ee5 cho ph\u00e9p c\u00e1c ph\u1ee5 thu\u1ed9c v\u00f2ng trong l\u1edbp tr\u1ef1c quan, trong khi b\u1ed9 \u0111\u1ed9ng c\u01a1 c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd t\u1eeb ch\u1ed1i ch\u00fang. Tr\u1ecdng t\u00e2m ph\u1ea3i lu\u00f4n n\u1eb1m \u1edf c\u00e1c quy t\u1eafc to\u00e0n v\u1eb9n quan h\u1ec7 thay v\u00ec giao di\u1ec7n v\u1ebd s\u01a1 \u0111\u1ed3.<\/p>\n

                \n
              • T\u00ednh nh\u1ea5t qu\u00e1n tr\u1ef1c quan:<\/strong>S\u1eed d\u1ee5ng c\u00e1c k\u00fd hi\u1ec7u chu\u1ea9n cho c\u00e1c m\u1ed1i quan h\u1ec7 (k\u00fd hi\u1ec7u ch\u00e2n chim).<\/li>\n
              • X\u00e1c minh:<\/strong>Ch\u1ea1y l\u01b0\u1ee3c \u0111\u1ed3 tr\u00ean c\u01a1 s\u1edf d\u1eef li\u1ec7u th\u1eed nghi\u1ec7m \u0111\u1ec3 x\u00e1c minh c\u00e1c r\u00e0ng bu\u1ed9c.<\/li>\n
              • H\u1ee3p t\u00e1c:<\/strong>Xem x\u00e9t s\u01a1 \u0111\u1ed3 c\u00f9ng c\u00e1c b\u00ean li\u00ean quan hi\u1ec3u r\u00f5 v\u1ec1 l\u0129nh v\u1ef1c kinh doanh, ch\u1ee9 kh\u00f4ng ch\u1ec9 nh\u1eefng \u0111\u1ed3ng nghi\u1ec7p k\u1ef9 thu\u1eadt.<\/li>\n<\/ul>\n

                9. C\u00e1c t\u00ecnh hu\u1ed1ng th\u1ef1c t\u1ebf th\u1ea5t b\u1ea1i \u26a0\ufe0f<\/h2>\n

                Hi\u1ec3u \u0111\u01b0\u1ee3c c\u00e1c kh\u00e1i ni\u1ec7m tr\u1eebu t\u01b0\u1ee3ng l\u00e0 m\u1ed9t chuy\u1ec7n; nh\u01b0ng th\u1ea5y ch\u00fang th\u1ea5t b\u1ea1i trong th\u1ef1c t\u1ebf l\u1ea1i l\u00e0 chuy\u1ec7n kh\u00e1c. D\u01b0\u1edbi \u0111\u00e2y l\u00e0 nh\u1eefng t\u00ecnh hu\u1ed1ng ph\u1ed5 bi\u1ebfn khi thi\u1ebft k\u1ebf ERD k\u00e9m d\u1eabn \u0111\u1ebfn c\u00e1c v\u1ea5n \u0111\u1ec1 c\u1ee5 th\u1ec3.<\/p>\n

                T\u00ecnh hu\u1ed1ng A: V\u00f2ng l\u1eb7p v\u00f4 h\u1ea1n<\/h3>\n

                M\u1ed9t nh\u00e0 ph\u00e1t tri\u1ec3n t\u1ea1o ra m\u1ed1i quan h\u1ec7 gi\u1eefa Ng\u01b0\u1eddi d\u00f9ng<\/code> v\u00e0 C\u00e1c nh\u00f3m<\/code>trong \u0111\u00f3 m\u1ed9t ng\u01b0\u1eddi d\u00f9ng thu\u1ed9c v\u1ec1 m\u1ed9t nh\u00f3m, v\u00e0 m\u1ed9t nh\u00f3m do m\u1ed9t ng\u01b0\u1eddi d\u00f9ng \u0111i\u1ec1u ph\u1ed1i. N\u1ebfu kh\u00f3a ngo\u1ea1i tr\u1ecf \u0111\u1ebfn c\u00f9ng m\u1ed9t b\u1ea3ng m\u00e0 kh\u00f4ng c\u00f3 g\u1ed1c r\u00f5 r\u00e0ng, l\u1ed7i tham chi\u1ebfu v\u00f2ng s\u1ebd x\u1ea3y ra khi ch\u00e8n d\u1eef li\u1ec7u. S\u01a1 \u0111\u1ed3 ERD ph\u1ea3i ph\u00e2n bi\u1ec7t r\u00f5 r\u00e0ng gi\u1eefa c\u00e1c m\u1ed1i quan h\u1ec7 ‘Th\u00e0nh vi\u00ean’ v\u00e0 ‘Tr\u01b0\u1edfng nh\u00f3m’.<\/p>\n

                T\u00ecnh hu\u1ed1ng B: M\u1ea5t d\u1eef li\u1ec7u \u00e2m th\u1ea7m<\/h3>\n

                M\u1ed9t \u0110\u01a1n h\u00e0ng<\/code>b\u1ea3ng tham chi\u1ebfu \u0111\u1ebfn m\u1ed9t S\u1ea3n ph\u1ea9m<\/code>b\u1ea3ng. Kh\u00f3a ON DELETE<\/code>\u0111\u01b0\u1ee3c thi\u1ebft l\u1eadp th\u00e0nh CASCADE<\/code>. Khi m\u1ed9t s\u1ea3n ph\u1ea9m b\u1ecb x\u00f3a kh\u1ecfi danh m\u1ee5c, t\u1ea5t c\u1ea3 c\u00e1c \u0111\u01a1n h\u00e0ng li\u00ean quan \u0111\u1ec1u b\u1ecb x\u00f3a. \u0110i\u1ec1u n\u00e0y ph\u00e1 h\u1ee7y d\u1eef li\u1ec7u b\u00e1n h\u00e0ng l\u1ecbch s\u1eed. S\u01a1 \u0111\u1ed3 ERD n\u00ean x\u00e1c \u0111\u1ecbnh r\u00f5 h\u00e0nh \u0111\u1ed9ng tham chi\u1ebfu l\u00e0 RESTRICT<\/code> ho\u1eb7c SET NULL<\/code>t\u00f9y theo nhu c\u1ea7u kinh doanh.<\/p>\n

                T\u00ecnh hu\u1ed1ng C: T\u00ecm ki\u1ebfm ch\u1eadm<\/h3>\n

                M\u1ed9t b\u1ea3ng \u0111\u01b0\u1ee3c t\u1ea1o v\u1edbi c\u1ed9t name<\/code>c\u1ed9t. C\u00e1c k\u1ef9 s\u01b0 truy v\u1ea5n b\u1ea3ng n\u00e0y th\u01b0\u1eddng xuy\u00ean \u0111\u1ec3 t\u00ecm ng\u01b0\u1eddi d\u00f9ng theo t\u00ean. N\u1ebfu kh\u00f4ng c\u00f3 ch\u1ec9 m\u1ee5c \u0111\u01b0\u1ee3c x\u00e1c \u0111\u1ecbnh t\u1eeb giai \u0111o\u1ea1n thi\u1ebft k\u1ebf, c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd th\u1ef1c hi\u1ec7n qu\u00e9t to\u00e0n b\u1ed9 b\u1ea3ng. S\u01a1 \u0111\u1ed3 ERD n\u00ean ch\u1ec9 r\u00f5 c\u00e1c c\u1ed9t n\u00e0o l\u00e0 tr\u1ecdng t\u00e2m t\u00ecm ki\u1ebfm v\u00e0 c\u1ea7n \u0111\u01b0\u1ee3c ch\u1ec9 m\u1ee5c h\u00f3a.<\/p>\n

                10. Ti\u1ebfn h\u00f3a t\u1eeb t\u01b0 duy c\u1ea5p \u0111\u1ed9 junior sang c\u1ea5p \u0111\u1ed9 senior \ud83d\ude80<\/h2>\n

                S\u1ef1 chuy\u1ec3n \u0111\u1ed5i n\u00e0y bao g\u1ed3m vi\u1ec7c thay \u0111\u1ed5i tr\u1ecdng t\u00e2m t\u1eeb ‘N\u00f3 c\u00f3 ho\u1ea1t \u0111\u1ed9ng kh\u00f4ng?’ sang ‘N\u00f3 c\u00f3 m\u1edf r\u1ed9ng \u0111\u01b0\u1ee3c kh\u00f4ng?’ v\u00e0 ‘N\u00f3 c\u00f3 d\u1ec5 b\u1ea3o tr\u00ec kh\u00f4ng?’<\/p>\n

                  \n
                • S\u1ef1 mong \u0111\u1ee3i:<\/strong>D\u1ef1 \u0111o\u00e1n c\u00e1c y\u00eau c\u1ea7u t\u01b0\u01a1ng lai d\u1ef1a tr\u00ean xu h\u01b0\u1edbng ng\u00e0nh.<\/li>\n
                • Giao ti\u1ebfp:<\/strong>Chuy\u1ec3n \u0111\u1ed5i c\u00e1c r\u00e0ng bu\u1ed9c k\u1ef9 thu\u1eadt th\u00e0nh r\u1ee7i ro kinh doanh.<\/li>\n
                • Xem x\u00e9t l\u1ea1i:<\/strong>Kh\u00f4ng bao gi\u1edd cho r\u1eb1ng m\u1ed9t s\u01a1 \u0111\u1ed3 l\u00e0 \u0111\u00fang n\u1ebfu ch\u01b0a \u0111\u01b0\u1ee3c xem x\u00e9t b\u1edfi \u0111\u1ed3ng nghi\u1ec7p.<\/li>\n<\/ul>\n

                  C\u00e1c k\u1ef9 s\u01b0 c\u1ea5p th\u1ea5p th\u01b0\u1eddng l\u00e0m vi\u1ec7c m\u1ed9t m\u00ecnh. C\u00e1c k\u1ef9 s\u01b0 c\u1ea5p cao h\u1ee3p t\u00e1c v\u1edbi nhau. ERD l\u00e0 m\u1ed9t c\u00f4ng c\u1ee5 giao ti\u1ebfp. N\u00f3 n\u1ed1i li\u1ec1n kho\u1ea3ng c\u00e1ch gi\u1eefa c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n, qu\u1ea3n l\u00fd s\u1ea3n ph\u1ea9m v\u00e0 c\u00e1c b\u00ean li\u00ean quan. N\u1ebfu s\u01a1 \u0111\u1ed3 g\u00e2y hi\u1ec3u l\u1ea7m, c\u00e1c k\u1ef3 v\u1ecdng s\u1ebd kh\u00f4ng c\u00f2n \u0111\u1ed3ng nh\u1ea5t.<\/p>\n

                  Suy ngh\u0129 cu\u1ed1i c\u00f9ng v\u1ec1 t\u00ednh to\u00e0n v\u1eb9n d\u1eef li\u1ec7u \ud83c\udfaf<\/h2>\n

                  X\u00e2y d\u1ef1ng l\u01b0\u1ee3c \u0111\u1ed3 c\u01a1 s\u1edf d\u1eef li\u1ec7u kh\u00f4ng ph\u1ea3i l\u00e0 m\u1ed9t c\u00f4ng vi\u1ec7c m\u1ed9t l\u1ea7n duy nh\u1ea5t; \u0111\u00f3 l\u00e0 m\u1ed9t k\u1ef7 lu\u1eadt li\u00ean t\u1ee5c. Kho\u1ea3ng c\u00e1ch ph\u1ee9c t\u1ea1p t\u1ed3n t\u1ea1i v\u00ec m\u1ee9c \u0111\u1ed9 r\u1ee7i ro cao. M\u1ed9t l\u1ed7i trong m\u00e3 \u1ee9ng d\u1ee5ng c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c s\u1eeda ngay l\u1eadp t\u1ee9c. M\u1ed9t l\u1ed7i trong m\u00f4 h\u00ecnh d\u1eef li\u1ec7u th\u01b0\u1eddng \u0111\u00f2i h\u1ecfi di d\u1eddi d\u1eef li\u1ec7u, d\u1ecdn d\u1eb9p d\u1eef li\u1ec7u v\u00e0 th\u1eddi gian ng\u1eebng ho\u1ea1t \u0111\u1ed9ng.<\/p>\n

                  B\u1eb1ng c\u00e1ch tu\u00e2n th\u1ee7 nghi\u00eam ng\u1eb7t c\u00e1c nguy\u00ean t\u1eafc m\u00f4 h\u00ecnh h\u00f3a, hi\u1ec3u s\u00e2u s\u1eafc v\u1ec1 t\u00ednh cardinality v\u00e0 \u01b0u ti\u00ean logic kinh doanh h\u01a1n ti\u1ec7n l\u1ee3i, c\u00e1c k\u1ef9 s\u01b0 c\u00f3 th\u1ec3 thu h\u1eb9p kho\u1ea3ng c\u00e1ch. M\u1ee5c ti\u00eau kh\u00f4ng ph\u1ea3i l\u00e0 t\u1ea1o ra m\u1ed9t s\u01a1 \u0111\u1ed3 ho\u00e0n h\u1ea3o, m\u00e0 l\u00e0 t\u1ea1o ra m\u1ed9t n\u1ec1n t\u1ea3ng h\u1ed7 tr\u1ee3 s\u1ef1 ph\u00e1t tri\u1ec3n c\u1ee7a ph\u1ea7n m\u1ec1m. D\u1eef li\u1ec7u l\u00e0 t\u00e0i s\u1ea3n qu\u00fd gi\u00e1 nh\u1ea5t m\u00e0 m\u1ed9t \u1ee9ng d\u1ee5ng s\u1edf h\u1eefu. B\u1ea3o v\u1ec7 c\u1ea5u tr\u00fac c\u1ee7a n\u00f3 l\u00e0 tr\u00e1ch nhi\u1ec7m c\u1ee7a m\u1ecdi k\u1ef9 s\u01b0 tham gia qu\u00e1 tr\u00ecnh x\u00e2y d\u1ef1ng.<\/p>\n

                  D\u00e0nh th\u1eddi gian \u0111\u1ec3 xem x\u00e9t l\u1ea1i s\u01a1 \u0111\u1ed3 c\u1ee7a b\u1ea1n. \u0110\u1eb7t c\u00e2u h\u1ecfi cho m\u1ecdi m\u1ed1i quan h\u1ec7. X\u00e1c minh t\u1eebng r\u00e0ng bu\u1ed9c. Th\u1eddi gian \u0111\u1ea7u t\u01b0 trong giai \u0111o\u1ea1n thi\u1ebft k\u1ebf s\u1ebd ti\u1ebft ki\u1ec7m h\u00e0ng th\u00e1ng c\u00f4ng s\u1ee9c trong giai \u0111o\u1ea1n b\u1ea3o tr\u00ec.<\/p>\n","protected":false},"excerpt":{"rendered":"

                  M\u00f4 h\u00ecnh h\u00f3a d\u1eef li\u1ec7u th\u01b0\u1eddng l\u00e0 n\u1ec1n t\u1ea3ng v\u00f4 h\u00ecnh c\u1ee7a b\u1ea5t k\u1ef3 \u1ee9ng d\u1ee5ng ph\u1ea7n m\u1ec1m n\u00e0o. Trong khi m\u00e3 ngu\u1ed3n th\u1ef1c thi logic kinh doanh \u0111\u01b0\u1ee3c ch\u00fa…<\/p>\n","protected":false},"author":1,"featured_media":1626,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_title":"Nh\u1eefng sai l\u1ea7m th\u01b0\u1eddng g\u1eb7p c\u1ee7a k\u1ef9 s\u01b0 c\u1ea5p th\u1ea5p khi v\u1ebd ERD: H\u01b0\u1edbng d\u1eabn to\u00e0n di\u1ec7n","_yoast_wpseo_metadesc":"Kh\u00e1m ph\u00e1 nh\u1eefng l\u1ed7i ph\u1ed5 bi\u1ebfn trong s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3. H\u1ecdc v\u1ec1 t\u00ednh cardinality, chu\u1ea9n h\u00f3a v\u00e0 nh\u1eefng \u0111i\u1ec3m sai s\u00f3t trong m\u00f4 h\u00ecnh h\u00f3a d\u1eef li\u1ec7u \u0111\u1ec3 c\u1ea3i thi\u1ec7n ki\u1ebfn tr\u00fac c\u01a1 s\u1edf d\u1eef li\u1ec7u c\u1ee7a b\u1ea1n.","fifu_image_url":"","fifu_image_alt":"","footnotes":""},"categories":[68],"tags":[89,92],"class_list":["post-1625","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-database-design","tag-academic","tag-erd"],"yoast_head":"\nNh\u1eefng sai l\u1ea7m th\u01b0\u1eddng g\u1eb7p c\u1ee7a k\u1ef9 s\u01b0 c\u1ea5p th\u1ea5p khi v\u1ebd ERD: H\u01b0\u1edbng d\u1eabn to\u00e0n di\u1ec7n<\/title>\n<meta name=\"description\" content=\"Kh\u00e1m ph\u00e1 nh\u1eefng l\u1ed7i ph\u1ed5 bi\u1ebfn trong s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3. 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