{"id":1563,"date":"2026-03-26T10:18:03","date_gmt":"2026-03-26T10:18:03","guid":{"rendered":"https:\/\/www.viz-read.com\/vi\/erd-explained-beginner-guide\/"},"modified":"2026-03-26T10:18:03","modified_gmt":"2026-03-26T10:18:03","slug":"erd-explained-beginner-guide","status":"publish","type":"post","link":"https:\/\/www.viz-read.com\/vi\/erd-explained-beginner-guide\/","title":{"rendered":"Gi\u1ea3i th\u00edch ERD: Con \u0111\u01b0\u1eddng r\u00f5 r\u00e0ng cho ng\u01b0\u1eddi m\u1edbi b\u1eaft \u0111\u1ea7u \u0111\u1ec3 th\u00e0nh th\u1ea1o thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u"},"content":{"rendered":"

T\u1ea1o ra m\u1ed9t c\u1ea5u tr\u00fac d\u1eef li\u1ec7u v\u1eefng ch\u1eafc l\u00e0 n\u1ec1n t\u1ea3ng cho b\u1ea5t k\u1ef3 \u1ee9ng d\u1ee5ng ph\u1ea7n m\u1ec1m \u0111\u00e1ng tin c\u1eady n\u00e0o. Khi b\u1ea1n b\u1eaft \u0111\u1ea7u x\u00e2y d\u1ef1ng c\u00e1c h\u1ec7 th\u1ed1ng l\u01b0u tr\u1eef th\u00f4ng tin, b\u1ea1n c\u1ea7n m\u1ed9t b\u1ea3n v\u1ebd thi\u1ebft k\u1ebf. B\u1ea3n v\u1ebd thi\u1ebft k\u1ebf \u0111\u00f3 ch\u00ednh l\u00e0 s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3, th\u01b0\u1eddng \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 ERD. Bi\u1ec3u \u0111\u1ed3 tr\u1ef1c quan n\u00e0y cho ph\u00e9p c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n v\u00e0 c\u00e1c b\u00ean li\u00ean quan hi\u1ec3u c\u00e1ch d\u1eef li\u1ec7u k\u1ebft n\u1ed1i v\u1edbi nhau tr\u01b0\u1edbc khi vi\u1ebft b\u1ea5t k\u1ef3 d\u00f2ng m\u00e3 n\u00e0o. Kh\u00f4ng c\u00f3 giai \u0111o\u1ea1n l\u1eadp k\u1ebf ho\u1ea1ch n\u00e0y, c\u01a1 s\u1edf d\u1eef li\u1ec7u th\u01b0\u1eddng tr\u1edf n\u00ean l\u1ed9n x\u1ed9n, ch\u1eadm ch\u1ea1p v\u00e0 kh\u00f3 b\u1ea3o tr\u00ec. \ud83c\udfd7\ufe0f<\/p>\n

H\u01b0\u1edbng d\u1eabn n\u00e0y ph\u00e2n t\u00edch c\u00e1c nguy\u00ean t\u1eafc c\u1ed1t l\u00f5i trong thi\u1ebft k\u1ebf ERD. Ch\u00fang ta s\u1ebd kh\u00e1m ph\u00e1 c\u00e1c th\u00e0nh ph\u1ea7n thi\u1ebft y\u1ebfu, c\u00e1c quy t\u1eafc \u0111i\u1ec1u ch\u1ec9nh m\u1ed1i quan h\u1ec7 d\u1eef li\u1ec7u, v\u00e0 c\u00e1c b\u01b0\u1edbc logic c\u1ea7n thi\u1ebft \u0111\u1ec3 x\u00e2y d\u1ef1ng m\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 c\u00f3 th\u1ec3 m\u1edf r\u1ed9ng. D\u00f9 b\u1ea1n l\u00e0 sinh vi\u00ean, nh\u00e0 ph\u00e1t tri\u1ec3n c\u1ea5p th\u1ea5p hay qu\u1ea3n l\u00fd s\u1ea3n ph\u1ea9m, vi\u1ec7c hi\u1ec3u r\u00f5 c\u00e1c kh\u00e1i ni\u1ec7m n\u00e0y s\u1ebd \u0111\u1ea3m b\u1ea3o ki\u1ebfn tr\u00fac d\u1eef li\u1ec7u c\u1ee7a b\u1ea1n lu\u00f4n v\u1eefng ch\u1eafc theo th\u1eddi gian.<\/p>\n

\n
\"Chalkboard-style<\/figure>\n<\/div>\n

ERD th\u1ef1c s\u1ef1 l\u00e0 g\u00ec? \ud83e\udd14<\/h2>\n

S\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 l\u00e0 m\u1ed9t m\u00f4 h\u00ecnh c\u1ea5p cao \u0111\u01b0\u1ee3c d\u00f9ng \u0111\u1ec3 m\u00f4 t\u1ea3 c\u1ea5u tr\u00fac c\u1ee7a c\u01a1 s\u1edf d\u1eef li\u1ec7u. N\u00f3 x\u00e1c \u0111\u1ecbnh c\u00e1c th\u1ef1c th\u1ec3, \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\u00e0 c\u00e1c m\u1ed1i quan h\u1ec7 t\u1ed3n t\u1ea1i gi\u1eefa ch\u00fang. H\u00e3y h\u00ecnh dung n\u00f3 nh\u01b0 m\u1ed9t b\u1ea3n \u0111\u1ed3 cho d\u1eef li\u1ec7u c\u1ee7a b\u1ea1n. T\u01b0\u01a1ng t\u1ef1 nh\u01b0 b\u1ea3n \u0111\u1ed3 th\u00e0nh ph\u1ed1 hi\u1ec3n th\u1ecb c\u00e1c con \u0111\u01b0\u1eddng k\u1ebft n\u1ed1i c\u00e1c khu ph\u1ed1, ERD th\u1ec3 hi\u1ec7n c\u00e1c b\u1ea3ng k\u1ebft n\u1ed1i c\u00e1c \u0111i\u1ec3m d\u1eef li\u1ec7u c\u1ee5 th\u1ec3.<\/p>\n

M\u1ee5c ti\u00eau ch\u00ednh c\u1ee7a bi\u1ec3u \u0111\u1ed3 n\u00e0y l\u00e0 truy\u1ec1n \u0111\u1ea1t c\u1ea5u tr\u00fac logic c\u1ee7a c\u01a1 s\u1edf d\u1eef li\u1ec7u. N\u00f3 \u0111\u00f3ng vai tr\u00f2 nh\u01b0 m\u1ed9t ng\u00f4n ng\u1eef chung gi\u1eefa c\u00e1c \u0111\u1ed9i k\u1ef9 thu\u1eadt v\u00e0 c\u00e1c nh\u00e0 ph\u00e2n t\u00edch kinh doanh. B\u1eb1ng c\u00e1ch tr\u1ef1c quan h\u00f3a lu\u1ed3ng d\u1eef li\u1ec7u, b\u1ea1n c\u00f3 th\u1ec3 ph\u00e1t hi\u1ec7n s\u1edbm c\u00e1c v\u1ea5n \u0111\u1ec1 ti\u1ec1m \u1ea9n, ch\u1eb3ng h\u1ea1n nh\u01b0 d\u1eef li\u1ec7u tr\u00f9ng l\u1eb7p ho\u1eb7c c\u00e1c li\u00ean k\u1ebft b\u1ecb thi\u1ebfu. C\u00e1ch ti\u1ebfp c\u1eadn ch\u1ee7 \u0111\u1ed9ng n\u00e0y gi\u00fap ti\u1ebft ki\u1ec7m th\u1eddi gian \u0111\u00e1ng k\u1ec3 trong giai \u0111o\u1ea1n ph\u00e1t tri\u1ec3n.<\/p>\n

Nh\u1eefng l\u1ee3i \u00edch ch\u00ednh khi s\u1eed d\u1ee5ng ERD bao g\u1ed3m:<\/p>\n

    \n
  • R\u00f5 r\u00e0ng:<\/strong>Tr\u1ef1c quan h\u00f3a c\u00e1c c\u1ea5u tr\u00fac d\u1eef li\u1ec7u ph\u1ee9c t\u1ea1p gi\u00fap ch\u00fang d\u1ec5 hi\u1ec3u h\u01a1n.<\/li>\n
  • T\u00ednh nh\u1ea5t qu\u00e1n:<\/strong>\u0110\u1ea3m b\u1ea3o t\u1ea5t c\u1ea3 c\u00e1c th\u00e0nh vi\u00ean trong nh\u00f3m \u0111\u1ec1u th\u1ed1ng nh\u1ea5t v\u1ec1 c\u00e1ch \u0111\u1ecbnh ngh\u0129a d\u1eef li\u1ec7u.<\/li>\n
  • Hi\u1ec7u qu\u1ea3:<\/strong>Gi\u00fap t\u1ed1i \u01b0u hi\u1ec7u su\u1ea5t truy v\u1ea5n b\u1eb1ng c\u00e1ch gi\u1ea3m c\u00e1c ph\u00e9p n\u1ed1i kh\u00f4ng c\u1ea7n thi\u1ebft.<\/li>\n
  • T\u00e0i li\u1ec7u:<\/strong>Ho\u1ea1t \u0111\u1ed9ng nh\u01b0 m\u1ed9t h\u01b0\u1edbng d\u1eabn tham kh\u1ea3o cho vi\u1ec7c b\u1ea3o tr\u00ec trong t\u01b0\u01a1ng lai.<\/li>\n<\/ul>\n

    C\u00e1c th\u00e0nh ph\u1ea7n c\u1ed1t l\u00f5i c\u1ee7a l\u01b0\u1ee3c \u0111\u1ed3 c\u01a1 s\u1edf d\u1eef li\u1ec7u \ud83d\udd11<\/h2>\n

    \u0110\u1ec3 x\u00e2y d\u1ef1ng bi\u1ec3u \u0111\u1ed3 m\u1ed9t c\u00e1ch hi\u1ec7u qu\u1ea3, b\u1ea1n ph\u1ea3i hi\u1ec3u r\u00f5 c\u00e1c kh\u1ed1i x\u00e2y d\u1ef1ng c\u01a1 b\u1ea3n. M\u1ed7i bi\u1ec3u \u0111\u1ed3 \u0111\u1ec1u d\u1ef1a tr\u00ean ba y\u1ebfu t\u1ed1 ch\u00ednh: th\u1ef1c th\u1ec3, thu\u1ed9c t\u00ednh v\u00e0 m\u1ed1i quan h\u1ec7. N\u1eafm v\u1eefng nh\u1eefng ki\u1ebfn th\u1ee9c n\u1ec1n t\u1ea3ng n\u00e0y s\u1ebd cung c\u1ea5p khung c\u1ea7n thi\u1ebft cho b\u1ea5t k\u1ef3 d\u1ef1 \u00e1n c\u01a1 s\u1edf d\u1eef li\u1ec7u n\u00e0o.<\/p>\n

    1. Th\u1ef1c th\u1ec3: C\u00e1c b\u1ea3ng \ud83d\udce6<\/h3>\n

    M\u1ed9t th\u1ef1c th\u1ec3 \u0111\u1ea1i di\u1ec7n cho m\u1ed9t \u0111\u1ed1i t\u01b0\u1ee3ng, con ng\u01b0\u1eddi ho\u1eb7c kh\u00e1i ni\u1ec7m c\u1ee5 th\u1ec3 trong l\u0129nh v\u1ef1c kinh doanh. Trong c\u01a1 s\u1edf d\u1eef li\u1ec7u quan h\u1ec7, m\u1ed9t th\u1ef1c th\u1ec3 t\u01b0\u01a1ng \u1ee9ng v\u1edbi m\u1ed9t b\u1ea3ng. M\u1ed7i b\u1ea3ng l\u01b0u tr\u1eef th\u00f4ng tin duy nh\u1ea5t v\u1ec1 th\u1ef1c th\u1ec3 \u0111\u00f3. V\u00ed d\u1ee5, trong h\u1ec7 th\u1ed1ng th\u01b0 vi\u1ec7n, \u201cS\u00e1ch\u201d v\u00e0 \u201cTh\u00e0nh vi\u00ean\u201d l\u00e0 hai th\u1ef1c th\u1ec3 kh\u00e1c nhau.<\/p>\n

    C\u00e1c th\u1ef1c th\u1ec3 th\u01b0\u1eddng \u0111\u01b0\u1ee3c bi\u1ec3u di\u1ec5n b\u1eb1ng h\u00ecnh ch\u1eef nh\u1eadt trong bi\u1ec3u \u0111\u1ed3. Ch\u00fang n\u00ean \u0111\u01b0\u1ee3c \u0111\u1eb7t t\u00ean b\u1eb1ng danh t\u1eeb s\u1ed1 \u00edt \u0111\u1ec3 ch\u1ec9 c\u00e1c tr\u01b0\u1eddng h\u1ee3p c\u1ee5 th\u1ec3. Khi \u0111\u1ecbnh ngh\u0129a m\u1ed9t th\u1ef1c th\u1ec3, b\u1ea1n \u0111ang th\u1ef1c s\u1ef1 \u0111\u1ecbnh ngh\u0129a m\u1ed9t danh m\u1ee5c d\u1eef li\u1ec7u.<\/p>\n

      \n
    • Th\u1ef1c th\u1ec3 m\u1ea1nh:<\/strong> Ch\u00fang t\u1ed3n t\u1ea1i \u0111\u1ed9c l\u1eadp. B\u1ea3ng \u201cKh\u00e1ch h\u00e0ng\u201d v\u1eabn t\u1ed3n t\u1ea1i ngay c\u1ea3 khi kh\u00f4ng c\u00f3 c\u00e1c b\u1ea3ng kh\u00e1c.<\/li>\n
    • Th\u1ef1c th\u1ec3 y\u1ebfu:<\/strong> Ch\u00fang ph\u1ee5 thu\u1ed9c v\u00e0o m\u1ed9t th\u1ef1c th\u1ec3 kh\u00e1c \u0111\u1ec3 t\u1ed3n t\u1ea1i. M\u1ed9t \u201cChi ti\u1ebft \u0111\u01a1n h\u00e0ng\u201d c\u00f3 th\u1ec3 l\u00e0 th\u1ef1c th\u1ec3 y\u1ebfu v\u00ec n\u00f3 ph\u1ee5 thu\u1ed9c v\u00e0o \u201c\u0110\u01a1n h\u00e0ng\u201d \u0111\u1ec3 c\u00f3 \u00fd ngh\u0129a.<\/li>\n<\/ul>\n

      2. Thu\u1ed9c t\u00ednh: C\u00e1c c\u1ed9t \ud83d\udcdd<\/h3>\n

      Thu\u1ed9c t\u00ednh l\u00e0 c\u00e1c \u0111\u1eb7c t\u00ednh ho\u1eb7c \u0111\u1eb7c \u0111i\u1ec3m m\u00f4 t\u1ea3 m\u1ed9t th\u1ef1c th\u1ec3. Trong m\u1ed9t b\u1ea3ng c\u01a1 s\u1edf d\u1eef li\u1ec7u, nh\u1eefng thu\u1ed9c t\u00ednh n\u00e0y tr\u1edf th\u00e0nh c\u00e1c c\u1ed9t. V\u00ed d\u1ee5, m\u1ed9t th\u1ef1c th\u1ec3 \u201cKh\u00e1ch h\u00e0ng\u201d c\u00f3 th\u1ec3 c\u00f3 c\u00e1c thu\u1ed9c t\u00ednh nh\u01b0 T\u00ean, Email v\u00e0 S\u1ed1 \u0111i\u1ec7n tho\u1ea1i.<\/p>\n

      C\u00e1c thu\u1ed9c t\u00ednh c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c ph\u00e2n lo\u1ea1i th\u00e0nh nhi\u1ec1u lo\u1ea1i:<\/p>\n

        \n
      • Thu\u1ed9c t\u00ednh \u0111\u01a1n gi\u1ea3n:<\/strong> Kh\u00f4ng th\u1ec3 chia nh\u1ecf h\u01a1n n\u1eefa, ch\u1eb3ng h\u1ea1n nh\u01b0 Tu\u1ed5i ho\u1eb7c Ng\u00e0y sinh.<\/li>\n
      • Thu\u1ed9c t\u00ednh h\u1ee3p th\u00e0nh:<\/strong> C\u00f3 th\u1ec3 chia th\u00e0nh c\u00e1c ph\u1ea7n ph\u1ee5, ch\u1eb3ng h\u1ea1n nh\u01b0 \u0110\u1ecba ch\u1ec9 (\u0110\u01b0\u1eddng, Th\u00e0nh ph\u1ed1, M\u00e3 b\u01b0u ch\u00ednh).<\/li>\n
      • Thu\u1ed9c t\u00ednh nhi\u1ec1u gi\u00e1 tr\u1ecb:<\/strong> C\u00f3 th\u1ec3 ch\u1ee9a nhi\u1ec1u gi\u00e1 tr\u1ecb, ch\u1eb3ng h\u1ea1n nh\u01b0 K\u1ef9 n\u0103ng ho\u1eb7c S\u1ed1 \u0111i\u1ec7n tho\u1ea1i.<\/li>\n
      • Thu\u1ed9c t\u00ednh \u0111\u01b0\u1ee3c suy ra:<\/strong> \u0110\u01b0\u1ee3c t\u00ednh to\u00e1n t\u1eeb c\u00e1c thu\u1ed9c t\u00ednh kh\u00e1c, ch\u1eb3ng h\u1ea1n nh\u01b0 Tu\u1ed5i (\u0111\u01b0\u1ee3c suy ra t\u1eeb Ng\u00e0y sinh).<\/li>\n<\/ul>\n

        3. M\u1ed1i quan h\u1ec7: C\u00e1c k\u1ebft n\u1ed1i \ud83d\udd04<\/h3>\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. \u0110\u00e2y l\u00e0 ph\u1ea7n quan tr\u1ecdng nh\u1ea5t trong thi\u1ebft k\u1ebf v\u00ec n\u00f3 quy\u1ebft \u0111\u1ecbnh c\u00e1ch d\u1eef li\u1ec7u \u0111\u01b0\u1ee3c li\u00ean k\u1ebft. Trong s\u01a1 \u0111\u1ed3, c\u00e1c m\u1ed1i quan h\u1ec7 \u0111\u01b0\u1ee3c th\u1ec3 hi\u1ec7n b\u1eb1ng h\u00ecnh thoi ho\u1eb7c c\u00e1c \u0111\u01b0\u1eddng n\u1ed1i gi\u1eefa c\u00e1c th\u1ef1c th\u1ec3.<\/p>\n

        V\u00ed d\u1ee5, m\u1ed9t “Kh\u00e1ch h\u00e0ng” \u0111\u1eb7t m\u1ed9t “\u0110\u01a1n h\u00e0ng”. \u0110\u00e2y l\u00e0 m\u1ed9t m\u1ed1i quan h\u1ec7. C\u01a1 s\u1edf d\u1eef li\u1ec7u ph\u1ea3i th\u1ef1c thi c\u00e1c quy t\u1eafc \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o kh\u00e1ch h\u00e0ng t\u1ed3n t\u1ea1i tr\u01b0\u1edbc khi \u0111\u01a1n h\u00e0ng c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c g\u00e1n cho h\u1ecd. \u0110i\u1ec1u n\u00e0y ng\u0103n ng\u1eeba d\u1eef li\u1ec7u b\u1ecb t\u00e1ch r\u1eddi.<\/p>\n

        Hi\u1ec3u r\u00f5 v\u1ec1 Cardinality v\u00e0 Modality \ud83d\udccf<\/h2>\n

        Cardinality x\u00e1c \u0111\u1ecbnh m\u1ed1i quan h\u1ec7 s\u1ed1 l\u01b0\u1ee3ng gi\u1eefa c\u00e1c b\u1ea3n ghi trong hai b\u1ea3ng li\u00ean quan. N\u00f3 tr\u1ea3 l\u1eddi c\u00e2u h\u1ecfi: “S\u1ed1 l\u01b0\u1ee3ng b\u1ea3n ghi c\u1ee7a Th\u1ef1c th\u1ec3 A li\u00ean quan \u0111\u1ebfn bao nhi\u00eau b\u1ea3n ghi c\u1ee7a Th\u1ef1c th\u1ec3 B?”. Hi\u1ec3u r\u00f5 \u0111i\u1ec1u n\u00e0y gi\u00fap ng\u0103n ng\u1eeba c\u00e1c b\u1ea5t th\u01b0\u1eddng trong d\u1eef li\u1ec7u.<\/p>\n

        C\u00f3 ba lo\u1ea1i cardinality ch\u00ednh:<\/p>\n

          \n
        1. M\u1ed9t-\u0111\u1ed1i-m\u1ed9t (1:1):<\/strong> M\u1ed9t b\u1ea3n ghi trong B\u1ea3ng A li\u00ean quan \u0111\u1ebfn \u0111\u00fang m\u1ed9t b\u1ea3n ghi trong B\u1ea3ng B.<\/li>\n
        2. M\u1ed9t-\u0111\u1ed1i-nhi\u1ec1u (1:N):<\/strong> M\u1ed9t b\u1ea3n ghi trong B\u1ea3ng A li\u00ean quan \u0111\u1ebfn nhi\u1ec1u b\u1ea3n ghi trong B\u1ea3ng B.<\/li>\n
        3. Nhi\u1ec1u-\u0111\u1ed1i-nhi\u1ec1u (M:N):<\/strong> Nhi\u1ec1u b\u1ea3n ghi trong B\u1ea3ng A li\u00ean quan \u0111\u1ebfn nhi\u1ec1u b\u1ea3n ghi trong B\u1ea3ng B.<\/li>\n<\/ol>\n

          D\u01b0\u1edbi \u0111\u00e2y l\u00e0 m\u1ed9t b\u1ea3ng minh h\u1ecda c\u00e1c m\u1ed1i quan h\u1ec7 n\u00e0y v\u1edbi c\u00e1c v\u00ed d\u1ee5 th\u1ef1c t\u1ebf.<\/p>\n\n\n\n\n\n\n\n
          Lo\u1ea1i Cardinality<\/th>\nB\u1ed1i c\u1ea3nh v\u00ed d\u1ee5<\/th>\nTri\u1ec3n khai<\/th>\n<\/tr>\n<\/thead>\n
          M\u1ed9t-\u0111\u1ed1i-m\u1ed9t (1:1)<\/td>\nNh\u00e2n vi\u00ean \u0111\u1ebfn H\u1ed9 chi\u1ebfu<\/td>\nKh\u00f3a ngo\u1ea1i trong m\u1ed9t b\u1ea3ng<\/td>\n<\/tr>\n
          M\u1ed9t-\u0111\u1ed1i-nhi\u1ec1u (1:N)<\/td>\nPh\u00f2ng ban \u0111\u1ebfn Nh\u00e2n vi\u00ean<\/td>\nKh\u00f3a ngo\u1ea1i trong b\u1ea3ng “Nhi\u1ec1u”<\/td>\n<\/tr>\n
          Nhi\u1ec1u-\u0111\u1ed1i-nhi\u1ec1u (M:N)<\/td>\nSinh vi\u00ean \u0111\u1ebfn Kh\u00f3a h\u1ecdc<\/td>\nB\u1ea3ng n\u1ed1i trung gian<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

          T\u00ednh kh\u1ea3 d\u1ee5ng th\u00eam m\u1ed9t l\u1edbp chi ti\u1ebft kh\u00e1c. N\u00f3 x\u00e1c \u0111\u1ecbnh m\u1ed1i quan h\u1ec7 l\u00e0 b\u1eaft bu\u1ed9c hay t\u00f9y ch\u1ecdn. V\u00ed d\u1ee5, m\u1ed9t \u0111\u01a1n h\u00e0ng c\u00f3 th\u1ec3 t\u1ed3n t\u1ea1i m\u00e0 kh\u00f4ng c\u1ea7n kh\u00e1ch h\u00e0ng kh\u00f4ng? Th\u01b0\u1eddng th\u00ec kh\u00f4ng. \u0110\u00e2y l\u00e0 m\u1ed1i quan h\u1ec7 b\u1eaft bu\u1ed9c. Kh\u00e1ch h\u00e0ng c\u00f3 th\u1ec3 kh\u00f4ng c\u00f3 \u0111\u01a1n h\u00e0ng n\u00e0o kh\u00f4ng? C\u00f3, \u0111i\u1ec1u n\u00e0y l\u00e0 t\u00f9y ch\u1ecdn.<\/p>\n

          Kh\u00f3a: Ch\u1ea5t k\u1ebft d\u00ednh cho t\u00ednh to\u00e0n v\u1eb9n c\u1ee7a d\u1eef li\u1ec7u \ud83d\udd17<\/h2>\n

          Kh\u00f3a l\u00e0 c\u00e1c thu\u1ed9c t\u00ednh c\u1ee5 th\u1ec3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 x\u00e1c \u0111\u1ecbnh duy nh\u1ea5t c\u00e1c b\u1ea3n ghi ho\u1eb7c li\u00ean k\u1ebft c\u00e1c b\u1ea3ng v\u1edbi nhau. Ch\u00fang l\u00e0 c\u01a1 ch\u1ebf \u0111\u1ea3m b\u1ea3o c\u00e1c m\u1ed1i quan h\u1ec7 v\u00e0 duy tr\u00ec t\u00ednh to\u00e0n v\u1eb9n c\u1ee7a d\u1eef li\u1ec7u.<\/p>\n

          Kh\u00f3a ch\u00ednh<\/h3>\n

          Kh\u00f3a ch\u00ednh (PK) x\u00e1c \u0111\u1ecbnh duy nh\u1ea5t m\u1ed7i b\u1ea3n ghi trong m\u1ed9t b\u1ea3ng. Kh\u00f4ng c\u00f3 hai h\u00e0ng n\u00e0o c\u00f3 th\u1ec3 c\u00f3 c\u00f9ng gi\u00e1 tr\u1ecb kh\u00f3a ch\u00ednh. N\u00f3 kh\u00f4ng th\u1ec3 l\u00e0 null. C\u00e1c l\u1ef1a ch\u1ecdn ph\u1ed5 bi\u1ebfn bao g\u1ed3m c\u00e1c s\u1ed1 nguy\u00ean t\u1ef1 t\u0103ng ho\u1eb7c UUID. \u0110i\u1ec1u n\u00e0y \u0111\u1ea3m b\u1ea3o m\u1ed7i ph\u1ea7n d\u1eef li\u1ec7u \u0111\u1ec1u c\u00f3 m\u1ed9t \u0111\u1ecba ch\u1ec9 duy nh\u1ea5t.<\/p>\n

          Kh\u00f3a ngo\u1ea1i<\/h3>\n

          Kh\u00f3a ngo\u1ea1i (FK) l\u00e0 m\u1ed9t tr\u01b0\u1eddng trong m\u1ed9t b\u1ea3ng tham chi\u1ebfu \u0111\u1ebfn kh\u00f3a ch\u00ednh trong m\u1ed9t b\u1ea3ng kh\u00e1c. N\u00f3 thi\u1ebft l\u1eadp li\u00ean k\u1ebft gi\u1eefa hai b\u1ea3ng. Khi b\u1ea1n \u0111\u1ecbnh ngh\u0129a kh\u00f3a ngo\u1ea1i, h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u s\u1ebd th\u1ef1c thi t\u00ednh to\u00e0n v\u1eb9n tham chi\u1ebfu. \u0110i\u1ec1u n\u00e0y c\u00f3 ngh\u0129a l\u00e0 b\u1ea1n kh\u00f4ng th\u1ec3 th\u00eam m\u1ed9t b\u1ea3n ghi v\u1edbi gi\u00e1 tr\u1ecb kh\u00f3a ngo\u1ea1i kh\u00f4ng t\u1ed3n t\u1ea1i trong b\u1ea3ng cha.<\/p>\n

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

          \u0110\u00f4i khi, m\u1ed9t c\u1ed9t duy nh\u1ea5t kh\u00f4ng \u0111\u1ee7 \u0111\u1ec3 x\u00e1c \u0111\u1ecbnh duy nh\u1ea5t m\u1ed9t b\u1ea3n ghi. Kh\u00f3a k\u1ebft h\u1ee3p k\u1ebft h\u1ee3p hai ho\u1eb7c nhi\u1ec1u c\u1ed9t \u0111\u1ec3 t\u1ea1o th\u00e0nh m\u1ed9t \u0111\u1ecbnh danh duy nh\u1ea5t. \u0110i\u1ec1u n\u00e0y th\u01b0\u1eddng x\u1ea3y ra trong c\u00e1c b\u1ea3ng li\u00ean k\u1ebft cho c\u00e1c m\u1ed1i quan h\u1ec7 nhi\u1ec1u-\u0111a.<\/p>\n

          Chu\u1ea9n h\u00f3a: S\u1eafp x\u1ebfp d\u1eef li\u1ec7u c\u1ee7a b\u1ea1n \ud83e\uddf9<\/h2>\n

          Chu\u1ea9n h\u00f3a l\u00e0 qu\u00e1 tr\u00ecnh s\u1eafp x\u1ebfp d\u1eef li\u1ec7u nh\u1eb1m gi\u1ea3m thi\u1ec3u s\u1ef1 tr\u00f9ng l\u1eb7p v\u00e0 c\u1ea3i thi\u1ec7n t\u00ednh to\u00e0n v\u1eb9n. N\u00f3 bao g\u1ed3m vi\u1ec7c chia nh\u1ecf c\u00e1c b\u1ea3ng l\u1edbn th\u00e0nh c\u00e1c b\u1ea3ng nh\u1ecf h\u01a1n, c\u00f3 li\u00ean k\u1ebft logic v\u1edbi nhau. Vi\u1ec7c tu\u00e2n theo c\u00e1c quy t\u1eafc n\u00e0y gi\u00fap tr\u00e1nh c\u00e1c b\u1ea5t th\u01b0\u1eddng trong qu\u00e1 tr\u00ecnh c\u1eadp nh\u1eadt, ch\u00e8n ho\u1eb7c x\u00f3a d\u1eef li\u1ec7u.<\/p>\n

          C\u00f3 nhi\u1ec1u d\u1ea1ng chu\u1ea9n h\u00f3a, nh\u01b0ng ba d\u1ea1ng \u0111\u1ea7u ti\u00ean l\u00e0 nh\u1eefng d\u1ea1ng th\u01b0\u1eddng \u0111\u01b0\u1ee3c \u00e1p d\u1ee5ng nh\u1ea5t:<\/p>\n

            \n
          • D\u1ea1ng chu\u1ea9n h\u00f3a th\u1ee9 nh\u1ea5t (1NF):<\/strong>Lo\u1ea1i b\u1ecf c\u00e1c c\u1ed9t tr\u00f9ng l\u1eb7p t\u1eeb c\u00f9ng m\u1ed9t b\u1ea3ng. T\u1ea1o c\u00e1c b\u1ea3ng ri\u00eang bi\u1ec7t cho d\u1eef li\u1ec7u li\u00ean quan v\u00e0 x\u00e1c \u0111\u1ecbnh m\u1ed7i h\u00e0ng b\u1eb1ng kh\u00f3a ch\u00ednh.<\/li>\n
          • D\u1ea1ng chu\u1ea9n h\u00f3a th\u1ee9 hai (2NF):<\/strong>\u0110\u00e1p \u1ee9ng t\u1ea5t c\u1ea3 c\u00e1c y\u00eau c\u1ea7u c\u1ee7a 1NF. Lo\u1ea1i b\u1ecf c\u00e1c t\u1eadp con d\u1eef li\u1ec7u \u00e1p d\u1ee5ng cho nhi\u1ec1u h\u00e0ng trong m\u1ed9t b\u1ea3ng v\u00e0 di chuy\u1ec3n ch\u00fang v\u00e0o c\u00e1c b\u1ea3ng ri\u00eang bi\u1ec7t.<\/li>\n
          • D\u1ea1ng chu\u1ea9n h\u00f3a th\u1ee9 ba (3NF):<\/strong>\u0110\u00e1p \u1ee9ng t\u1ea5t c\u1ea3 c\u00e1c y\u00eau c\u1ea7u c\u1ee7a 2NF. Lo\u1ea1i b\u1ecf c\u00e1c c\u1ed9t kh\u00f4ng ph\u1ee5 thu\u1ed9c v\u00e0o kh\u00f3a ch\u00ednh.<\/li>\n<\/ul>\n

            M\u1eb7c d\u00f9 c\u00e1c d\u1ea1ng cao h\u01a1n t\u1ed3n t\u1ea1i (4NF, 5NF), \u0111\u1ea1t \u0111\u1ebfn 3NF th\u01b0\u1eddng l\u00e0 \u0111\u1ee7 cho ph\u1ea7n l\u1edbn \u1ee9ng d\u1ee5ng. Chu\u1ea9n h\u00f3a qu\u00e1 m\u1ee9c c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn c\u00e1c truy v\u1ea5n ph\u1ee9c t\u1ea1p y\u00eau c\u1ea7u nhi\u1ec1u ph\u00e9p n\u1ed1i, \u0111i\u1ec1u n\u00e0y c\u00f3 th\u1ec3 \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn hi\u1ec7u su\u1ea5t. C\u00e2n b\u1eb1ng l\u00e0 ch\u00eca kh\u00f3a.<\/p>\n

            C\u00e1c b\u01b0\u1edbc \u0111\u1ec3 t\u1ea1o s\u01a1 \u0111\u1ed3 ERD \ud83d\udee0\ufe0f<\/h2>\n

            Thi\u1ebft k\u1ebf m\u1ed9t s\u01a1 \u0111\u1ed3 l\u00e0 m\u1ed9t qu\u00e1 tr\u00ecnh c\u00f3 h\u1ec7 th\u1ed1ng. B\u1ea1n kh\u00f4ng b\u1eaft \u0111\u1ea7u b\u1eb1ng vi\u1ec7c v\u1ebd h\u00ecnh d\u1ea1ng; b\u1ea1n b\u1eaft \u0111\u1ea7u b\u1eb1ng vi\u1ec7c hi\u1ec3u r\u00f5 y\u00eau c\u1ea7u. L\u00e0m theo c\u00e1c b\u01b0\u1edbc sau \u0111\u1ec3 t\u1ea1o ra m\u1ed9t m\u00f4 h\u00ecnh \u0111\u00e1ng tin c\u1eady.<\/p>\n

            B\u01b0\u1edbc 1: X\u00e1c \u0111\u1ecbnh c\u00e1c th\u1ef1c th\u1ec3<\/h3>\n

            Xem x\u00e9t c\u00e1c y\u00eau c\u1ea7u kinh doanh. T\u00ecm c\u00e1c danh t\u1eeb trong m\u00f4 t\u1ea3 \u0111\u1ea1i di\u1ec7n cho c\u00e1c \u0111\u1ed1i t\u01b0\u1ee3ng ho\u1eb7c con ng\u01b0\u1eddi. N\u1ebfu y\u00eau c\u1ea7u n\u00f3i r\u1eb1ng \u201cTheo d\u00f5i m\u1ecdi l\u1ea7n \u0111\u0103ng nh\u1eadp c\u1ee7a ng\u01b0\u1eddi d\u00f9ng\u201d, th\u00ec th\u1ef1c th\u1ec3 l\u00e0 \u201cNg\u01b0\u1eddi d\u00f9ng\u201d ho\u1eb7c \u201c\u0110\u0103ng nh\u1eadp\u201d. Li\u1ec7t k\u00ea t\u1ea5t c\u1ea3 c\u00e1c th\u1ef1c th\u1ec3 ti\u1ec1m n\u0103ng.<\/p>\n

            B\u01b0\u1edbc 2: X\u00e1c \u0111\u1ecbnh thu\u1ed9c t\u00ednh<\/h3>\n

            V\u1edbi m\u1ed7i th\u1ef1c th\u1ec3, x\u00e1c \u0111\u1ecbnh th\u00f4ng tin n\u00e0o c\u1ea7n \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef. H\u1ecfi xem nh\u1eefng chi ti\u1ebft n\u00e0o l\u00e0 c\u1ea7n thi\u1ebft \u0111\u1ec3 m\u00f4 t\u1ea3 \u0111\u1ea7y \u0111\u1ee7 th\u1ef1c th\u1ec3. V\u1edbi th\u1ef1c th\u1ec3 \u201cNg\u01b0\u1eddi d\u00f9ng\u201d, b\u1ea1n c\u00f3 th\u1ec3 c\u1ea7n Username, M\u1eadt kh\u1ea9u v\u00e0 Email.<\/p>\n

            B\u01b0\u1edbc 3: X\u00e1c \u0111\u1ecbnh c\u00e1c m\u1ed1i quan h\u1ec7<\/h3>\n

            K\u1ebft n\u1ed1i c\u00e1c th\u1ef1c th\u1ec3 d\u1ef1a tr\u00ean c\u00e1ch ch\u00fang t\u01b0\u01a1ng t\u00e1c v\u1edbi nhau. H\u1ecfi xem c\u00e1c th\u1ef1c th\u1ec3 li\u00ean quan nh\u01b0 th\u1ebf n\u00e0o. M\u1ed9t ng\u01b0\u1eddi d\u00f9ng c\u00f3 th\u1ec3 c\u00f3 nhi\u1ec1u l\u1ea7n \u0111\u0103ng nh\u1eadp kh\u00f4ng? M\u1ed9t s\u1ea3n ph\u1ea9m c\u00f3 thu\u1ed9c v\u1ec1 m\u1ed9t danh m\u1ee5c kh\u00f4ng? V\u1ebd c\u00e1c \u0111\u01b0\u1eddng n\u1ed1i v\u00e0 x\u00e1c \u0111\u1ecbnh t\u00ednh b\u1ed9i s\u1ed1.<\/p>\n

            B\u01b0\u1edbc 4: G\u00e1n kh\u00f3a<\/h3>\n

            X\u00e1c \u0111\u1ecbnh kh\u00f3a ch\u00ednh cho m\u1ed7i th\u1ef1c th\u1ec3. Sau \u0111\u00f3, th\u00eam kh\u00f3a ngo\u1ea1i t\u1ea1i nh\u1eefng n\u01a1i c\u00f3 m\u1ed1i quan h\u1ec7. B\u01b0\u1edbc n\u00e0y bi\u1ebfn s\u01a1 \u0111\u1ed3 kh\u00e1i ni\u1ec7m th\u00e0nh m\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 logic s\u1eb5n s\u00e0ng cho tri\u1ec3n khai.<\/p>\n

            B\u01b0\u1edbc 5: Xem x\u00e9t v\u00e0 tinh ch\u1ec9nh<\/h3>\n

            \u0110i qua m\u00f4 h\u00ecnh c\u00f9ng c\u00e1c b\u00ean li\u00ean quan. Ki\u1ec3m tra xem c\u00f3 \u0111i\u1ec3m d\u1eef li\u1ec7u b\u1ecb thi\u1ebfu hay m\u1ed1i quan h\u1ec7 sai kh\u00f4ng. \u0110\u1ea3m b\u1ea3o thi\u1ebft k\u1ebf h\u1ed7 tr\u1ee3 c\u00e1c truy v\u1ea5n mong mu\u1ed1n. Tinh ch\u1ec9nh s\u01a1 \u0111\u1ed3 cho \u0111\u1ebfn khi \u0111\u00e1p \u1ee9ng t\u1ea5t c\u1ea3 nhu c\u1ea7u kinh doanh.<\/p>\n

            Nh\u1eefng sai l\u1ea7m ph\u1ed5 bi\u1ebfn c\u1ea7n tr\u00e1nh \u26a0\ufe0f<\/h2>\n

            Ngay c\u1ea3 nh\u1eefng nh\u00e0 thi\u1ebft k\u1ebf c\u00f3 kinh nghi\u1ec7m c\u0169ng m\u1eafc sai l\u1ea7m. Nh\u1eadn th\u1ee9c \u0111\u01b0\u1ee3c nh\u1eefng l\u1ed7i ph\u1ed5 bi\u1ebfn s\u1ebd gi\u00fap b\u1ea1n x\u00e2y d\u1ef1ng h\u1ec7 th\u1ed1ng s\u1ea1ch s\u1ebd h\u01a1n. D\u01b0\u1edbi \u0111\u00e2y l\u00e0 nh\u1eefng v\u1ea5n \u0111\u1ec1 c\u1ea7n l\u01b0u \u00fd trong giai \u0111o\u1ea1n thi\u1ebft k\u1ebf.<\/p>\n

              \n
            • M\u1ed1i quan h\u1ec7 b\u1ecb thi\u1ebfu:<\/strong> Vi\u1ec7c qu\u00ean k\u1ebft n\u1ed1i c\u00e1c b\u1ea3ng c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn c\u00e1c h\u00f2m d\u1eef li\u1ec7u c\u00f4 l\u1eadp, n\u01a1i th\u00f4ng tin kh\u00f4ng th\u1ec3 \u0111\u01b0\u1ee3c k\u1ebft h\u1ee3p.<\/li>\n
            • D\u1eef li\u1ec7u tr\u00f9ng l\u1eb7p:<\/strong>L\u01b0u tr\u1eef c\u00f9ng m\u1ed9t th\u00f4ng tin trong nhi\u1ec1u b\u1ea3ng l\u00e0m t\u0103ng dung l\u01b0\u1ee3ng l\u01b0u tr\u1eef v\u00e0 l\u00e0m t\u0103ng nguy c\u01a1 b\u1ea5t nh\u1ea5t.<\/li>\n
            • \u0110\u1ed9 cardinality sai:<\/strong>\u0110\u1eb7t m\u1ed1i quan h\u1ec7 l\u00e0 m\u1ed9t-nhi\u1ec1u khi th\u1ef1c t\u1ebf ph\u1ea3i l\u00e0 nhi\u1ec1u-nhi\u1ec1u s\u1ebd t\u1ea1o ra l\u1ed7i x\u00e1c th\u1ef1c.<\/li>\n
            • Xung \u0111\u1ed9t t\u00ean g\u1ecdi:<\/strong>S\u1eed d\u1ee5ng t\u00ean m\u01a1 h\u1ed3 nh\u01b0 \u201cData1\u201d hay \u201cTableA\u201d khi\u1ebfn s\u01a1 \u0111\u1ed3 tr\u1edf n\u00ean kh\u00f3 hi\u1ec3u v\u1ec1 sau.<\/li>\n
            • B\u1ecf qua kh\u1ea3 n\u0103ng null:<\/strong>Kh\u00f4ng ch\u1ec9 r\u00f5 m\u1ed9t c\u1ed9t c\u00f3 cho ph\u00e9p gi\u00e1 tr\u1ecb null hay kh\u00f4ng c\u00f3 th\u1ec3 g\u00e2y ra l\u1ed7i b\u1ea5t ng\u1edd trong qu\u00e1 tr\u00ecnh nh\u1eadp d\u1eef li\u1ec7u.<\/li>\n<\/ul>\n

              C\u00e1c k\u00fd hi\u1ec7u tr\u1ef1c quan \ud83c\udfa8<\/h2>\n

              C\u00e1c nh\u00f3m kh\u00e1c nhau s\u1eed d\u1ee5ng c\u00e1c phong c\u00e1ch kh\u00e1c nhau \u0111\u1ec3 v\u1ebd s\u01a1 \u0111\u1ed3 ERD. Hai chu\u1ea9n ph\u1ed5 bi\u1ebfn nh\u1ea5t l\u00e0 k\u00fd hi\u1ec7u Crow\u2019s Foot v\u00e0 k\u00fd hi\u1ec7u Chen.<\/p>\n

                \n
              • K\u00fd hi\u1ec7u Crow\u2019s Foot:<\/strong>S\u1eed d\u1ee5ng c\u00e1c \u0111\u01b0\u1eddng c\u00f3 \u0111\u1ea7u cu\u1ed1i c\u1ee5 th\u1ec3 \u0111\u1ec3 bi\u1ec3u th\u1ecb \u0111\u1ed9 cardinality. M\u1ed9t \u0111\u01b0\u1eddng \u0111\u01a1n ngh\u0129a l\u00e0 m\u1ed9t, \u0111\u01b0\u1eddng chia nh\u00e1nh ngh\u0129a l\u00e0 nhi\u1ec1u. K\u00fd hi\u1ec7u n\u00e0y \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng r\u1ed9ng r\u00e3i trong c\u00e1c c\u00f4ng c\u1ee5 hi\u1ec7n \u0111\u1ea1i.<\/li>\n
              • K\u00fd hi\u1ec7u Chen:<\/strong>S\u1eed d\u1ee5ng h\u00ecnh thoi cho m\u1ed1i quan h\u1ec7 v\u00e0 h\u00ecnh elip cho thu\u1ed9c t\u00ednh. K\u00fd hi\u1ec7u n\u00e0y chi ti\u1ebft h\u01a1n nh\u01b0ng c\u00f3 th\u1ec3 tr\u1edf n\u00ean l\u1ed9n x\u1ed9n trong c\u00e1c h\u1ec7 th\u1ed1ng ph\u1ee9c t\u1ea1p.<\/li>\n<\/ul>\n

                D\u00f9 s\u1eed d\u1ee5ng k\u00fd hi\u1ec7u n\u00e0o, s\u1ef1 r\u00f5 r\u00e0ng l\u00e0 \u0111i\u1ec1u t\u1ed1i quan tr\u1ecdng. S\u01a1 \u0111\u1ed3 ph\u1ea3i d\u1ec5 \u0111\u1ecdc \u0111\u1ed1i v\u1edbi b\u1ea5t k\u1ef3 ai tham gia d\u1ef1 \u00e1n, ch\u1ee9 kh\u00f4ng ch\u1ec9 ri\u00eang qu\u1ea3n tr\u1ecb vi\u00ean c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/p>\n

                T\u1eeb \u00fd t\u01b0\u1edfng \u0111\u1ebfn tri\u1ec3n khai th\u1ef1c t\u1ebf \ud83d\ude80<\/h2>\n

                Khi thi\u1ebft k\u1ebf logic \u0111\u00e3 ho\u00e0n t\u1ea5t, n\u00f3 ph\u1ea3i \u0111\u01b0\u1ee3c chuy\u1ec3n \u0111\u1ed5i th\u00e0nh c\u01a1 s\u1edf d\u1eef li\u1ec7u th\u1ef1c t\u1ebf. Qu\u00e1 tr\u00ecnh n\u00e0y bao g\u1ed3m vi\u1ec7c ch\u1ecdn ki\u1ec3u d\u1eef li\u1ec7u v\u00e0 t\u1ed1i \u01b0u h\u00f3a hi\u1ec7u su\u1ea5t.<\/p>\n

                Trong giai \u0111o\u1ea1n n\u00e0y, b\u1ea1n ch\u1ecdn ki\u1ec3u d\u1eef li\u1ec7u c\u1ee5 th\u1ec3 cho c\u00e1c thu\u1ed9c t\u00ednh c\u1ee7a m\u00ecnh. V\u00ed d\u1ee5, m\u1ed9t tr\u01b0\u1eddng ng\u00e0y th\u00e1ng n\u00ean d\u00f9ng ki\u1ec3u Date, ch\u1ee9 kh\u00f4ng ph\u1ea3i chu\u1ed7i. Tr\u01b0\u1eddng gi\u00e1 ti\u1ec1n n\u00ean d\u00f9ng ki\u1ec3u Decimal, ch\u1ee9 kh\u00f4ng ph\u1ea3i Integer, \u0111\u1ec3 x\u1eed l\u00fd c\u00e1c ph\u00e2n s\u1ed1. Nh\u1eefng l\u1ef1a ch\u1ecdn n\u00e0y \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn k\u00edch th\u01b0\u1edbc l\u01b0u tr\u1eef v\u00e0 t\u1ed1c \u0111\u1ed9 truy v\u1ea5n.<\/p>\n

                Vi\u1ec7c t\u1ea1o ch\u1ec9 m\u1ee5c c\u0169ng r\u1ea5t quan tr\u1ecdng. T\u1ea1o ch\u1ec9 m\u1ee5c cho c\u00e1c c\u1ed9t th\u01b0\u1eddng xuy\u00ean \u0111\u01b0\u1ee3c t\u00ecm ki\u1ebfm, \u0111\u1eb7c bi\u1ec7t l\u00e0 c\u00e1c kh\u00f3a ngo\u1ea1i, s\u1ebd l\u00e0m t\u0103ng t\u1ed1c \u0111\u1ed9 truy xu\u1ea5t. Tuy nhi\u00ean, qu\u00e1 nhi\u1ec1u ch\u1ec9 m\u1ee5c c\u00f3 th\u1ec3 l\u00e0m ch\u1eadm thao t\u00e1c ghi. H\u00e3y t\u00ecm ra s\u1ef1 c\u00e2n b\u1eb1ng ph\u00f9 h\u1ee3p v\u1edbi kh\u1ed1i l\u01b0\u1ee3ng c\u00f4ng vi\u1ec7c c\u1ee7a b\u1ea1n.<\/p>\n

                T\u1ea1i sao l\u1eadp k\u1ebf ho\u1ea1ch quan tr\u1ecdng h\u01a1n t\u1ed1c \u0111\u1ed9 \u23f3<\/h2>\n

                R\u1ea5t d\u1ec5 b\u1ecb c\u00e1m d\u1ed7 b\u1ecf qua giai \u0111o\u1ea1n thi\u1ebft k\u1ebf v\u00e0 b\u1eaft \u0111\u1ea7u vi\u1ebft m\u00e3 ngay l\u1eadp t\u1ee9c. Tuy nhi\u00ean, vi\u1ec7c thay \u0111\u1ed5i c\u1ea5u tr\u00fac c\u01a1 s\u1edf d\u1eef li\u1ec7u v\u1ec1 sau l\u00e0 r\u1ea5t t\u1ed1n k\u00e9m. X\u00f3a d\u1eef li\u1ec7u ho\u1eb7c thay \u0111\u1ed5i c\u1ed9t c\u00f3 th\u1ec3 l\u00e0m h\u1ecfng c\u00e1c \u1ee9ng d\u1ee5ng hi\u1ec7n c\u00f3.<\/p>\n

                M\u1ed9t s\u01a1 \u0111\u1ed3 ERD \u0111\u01b0\u1ee3c suy ngh\u0129 k\u1ef9 s\u1ebd ho\u1ea1t \u0111\u1ed9ng nh\u01b0 m\u1ed9t h\u1ee3p \u0111\u1ed3ng. N\u00f3 \u0111\u1ecbnh ngh\u0129a c\u00e1c quy t\u1eafc t\u01b0\u01a1ng t\u00e1c d\u1eef li\u1ec7u. N\u1ebfu b\u1ea1n tu\u00e2n th\u1ee7 k\u1ebf ho\u1ea1ch, qu\u00e1 tr\u00ecnh ph\u00e1t tri\u1ec3n s\u1ebd tr\u01a1n tru h\u01a1n. N\u1ebfu b\u1ea1n thay \u0111\u1ed5i m\u00e0 kh\u00f4ng c\u1eadp nh\u1eadt s\u01a1 \u0111\u1ed3, n\u1ee3 k\u1ef9 thu\u1eadt s\u1ebd t\u00edch t\u1ee5 nhanh ch\u00f3ng.<\/p>\n

                \u0110\u1ea7u t\u01b0 th\u1eddi gian v\u00e0o giai \u0111o\u1ea1n l\u1eadp k\u1ebf ho\u1ea1ch s\u1ebd gi\u1ea3m nhu c\u1ea7u t\u00e1i c\u1ea5u tr\u00fac. N\u00f3 \u0111\u1ea3m b\u1ea3o h\u1ec7 th\u1ed1ng c\u00f3 th\u1ec3 x\u1eed l\u00fd s\u1ef1 ph\u00e1t tri\u1ec3n trong t\u01b0\u01a1ng lai. M\u1ed9t thi\u1ebft k\u1ebf c\u00f3 th\u1ec3 m\u1edf r\u1ed9ng s\u1ebd h\u1ed7 tr\u1ee3 c\u00e1c t\u00ednh n\u0103ng m\u1edbi m\u00e0 kh\u00f4ng c\u1ea7n x\u00e2y d\u1ef1ng l\u1ea1i ho\u00e0n to\u00e0n.<\/p>\n

                Nh\u1eefng suy ngh\u0129 cu\u1ed1i c\u00f9ng v\u1ec1 ki\u1ebfn tr\u00fac d\u1eef li\u1ec7u \ud83c\udfc1<\/h2>\n

                Thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u l\u00e0 s\u1ef1 k\u1ebft h\u1ee3p gi\u1eefa l\u00fd tr\u00ed v\u00e0 t\u1ea7m nh\u00ecn xa. N\u00f3 \u0111\u00f2i h\u1ecfi hi\u1ec3u s\u00e2u s\u1eafc v\u1ec1 l\u0129nh v\u1ef1c kinh doanh. S\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 l\u00e0 c\u00f4ng c\u1ee5 n\u1ed1i li\u1ec1n kho\u1ea3ng c\u00e1ch gi\u1eefa c\u00e1c y\u00eau c\u1ea7u tr\u1eebu t\u01b0\u1ee3ng v\u00e0 m\u00e3 th\u1ef1c t\u1ebf.<\/p>\n

                B\u1eb1ng c\u00e1ch t\u1eadp trung v\u00e0o c\u00e1c th\u1ef1c th\u1ec3, thu\u1ed9c t\u00ednh v\u00e0 m\u1ed1i quan h\u1ec7, b\u1ea1n s\u1ebd t\u1ea1o ra m\u1ed9t c\u1ea5u tr\u00fac h\u1ed7 tr\u1ee3 qu\u1ea3n l\u00fd d\u1eef li\u1ec7u ch\u00ednh x\u00e1c v\u00e0 hi\u1ec7u qu\u1ea3. Tu\u00e2n th\u1ee7 c\u00e1c quy t\u1eafc chu\u1ea9n h\u00f3a \u0111\u1ea3m b\u1ea3o t\u00ednh to\u00e0n v\u1eb9n, trong khi c\u00e1c kh\u00f3a r\u00f5 r\u00e0ng duy tr\u00ec c\u00e1c k\u1ebft n\u1ed1i.<\/p>\n

                H\u00e3y nh\u1edb r\u1eb1ng \u0111\u00e2y l\u00e0 m\u1ed9t qu\u00e1 tr\u00ecnh l\u1eb7p l\u1ea1i. Khi y\u00eau c\u1ea7u thay \u0111\u1ed5i, s\u01a1 \u0111\u1ed3 c\u0169ng c\u1ea7n thay \u0111\u1ed5i theo. Vi\u1ec7c c\u1eadp nh\u1eadt t\u00e0i li\u1ec7u \u0111\u1ea7y \u0111\u1ee7 l\u00e0 quan tr\u1ecdng kh\u00f4ng k\u00e9m g\u00ec thi\u1ebft k\u1ebf ban \u0111\u1ea7u. V\u1edbi n\u1ec1n t\u1ea3ng v\u1eefng ch\u1eafc, \u1ee9ng d\u1ee5ng c\u1ee7a b\u1ea1n s\u1ebd ho\u1ea1t \u0111\u1ed9ng \u1ed5n \u0111\u1ecbnh v\u00e0 m\u1edf r\u1ed9ng hi\u1ec7u qu\u1ea3.<\/p>\n

                B\u1eaft \u0111\u1ea7u nh\u1ecf, suy ngh\u0129 l\u1edbn, v\u00e0 lu\u00f4n \u01b0u ti\u00ean s\u1ef1 r\u00f5 r\u00e0ng trong m\u00f4 h\u00ecnh d\u1eef li\u1ec7u c\u1ee7a b\u1ea1n. C\u00e1ch ti\u1ebfp c\u1eadn n\u00e0y d\u1eabn \u0111\u1ebfn c\u00e1c h\u1ec7 th\u1ed1ng b\u1ec1n v\u1eefng v\u01b0\u1ee3t qua th\u1eed th\u00e1ch c\u1ee7a th\u1eddi gian.<\/p>\n","protected":false},"excerpt":{"rendered":"

                T\u1ea1o ra m\u1ed9t c\u1ea5u tr\u00fac d\u1eef li\u1ec7u v\u1eefng ch\u1eafc l\u00e0 n\u1ec1n t\u1ea3ng cho b\u1ea5t k\u1ef3 \u1ee9ng d\u1ee5ng ph\u1ea7n m\u1ec1m \u0111\u00e1ng tin c\u1eady n\u00e0o. Khi b\u1ea1n b\u1eaft \u0111\u1ea7u x\u00e2y d\u1ef1ng c\u00e1c…<\/p>\n","protected":false},"author":1,"featured_media":1564,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_title":"Gi\u1ea3i th\u00edch ERD: Con \u0111\u01b0\u1eddng r\u00f5 r\u00e0ng \u0111\u1ebfn h\u01b0\u1edbng d\u1eabn thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u","_yoast_wpseo_metadesc":"H\u1ecdc c\u00e1ch thi\u1ebft k\u1ebf c\u00e1c c\u01a1 s\u1edf d\u1eef li\u1ec7u m\u1ea1nh m\u1ebd v\u1edbi ERD. Hi\u1ec3u r\u00f5 c\u00e1c th\u1ef1c th\u1ec3, m\u1ed1i quan h\u1ec7 v\u00e0 kh\u00f3a m\u00e0 kh\u00f4ng c\u00f2n b\u1ed1i r\u1ed1i. M\u1ed9t h\u01b0\u1edbng d\u1eabn to\u00e0n di\u1ec7n d\u00e0nh cho ng\u01b0\u1eddi m\u1edbi b\u1eaft \u0111\u1ea7u.","fifu_image_url":"","fifu_image_alt":"","footnotes":""},"categories":[88],"tags":[84,87],"class_list":["post-1563","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-erd","tag-academic","tag-erd"],"yoast_head":"\nGi\u1ea3i th\u00edch ERD: Con \u0111\u01b0\u1eddng r\u00f5 r\u00e0ng \u0111\u1ebfn h\u01b0\u1edbng d\u1eabn thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u<\/title>\n<meta name=\"description\" content=\"H\u1ecdc c\u00e1ch thi\u1ebft k\u1ebf c\u00e1c c\u01a1 s\u1edf d\u1eef li\u1ec7u m\u1ea1nh m\u1ebd v\u1edbi ERD. Hi\u1ec3u r\u00f5 c\u00e1c th\u1ef1c th\u1ec3, m\u1ed1i quan h\u1ec7 v\u00e0 kh\u00f3a m\u00e0 kh\u00f4ng c\u00f2n b\u1ed1i r\u1ed1i. M\u1ed9t h\u01b0\u1edbng d\u1eabn to\u00e0n di\u1ec7n d\u00e0nh cho ng\u01b0\u1eddi m\u1edbi b\u1eaft \u0111\u1ea7u.\" \/>\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-read.com\/vi\/erd-explained-beginner-guide\/\" \/>\n<meta property=\"og:locale\" content=\"vi_VN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Gi\u1ea3i th\u00edch ERD: Con \u0111\u01b0\u1eddng r\u00f5 r\u00e0ng \u0111\u1ebfn h\u01b0\u1edbng d\u1eabn thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u\" \/>\n<meta property=\"og:description\" content=\"H\u1ecdc c\u00e1ch thi\u1ebft k\u1ebf c\u00e1c c\u01a1 s\u1edf d\u1eef li\u1ec7u m\u1ea1nh m\u1ebd v\u1edbi ERD. Hi\u1ec3u r\u00f5 c\u00e1c th\u1ef1c th\u1ec3, m\u1ed1i quan h\u1ec7 v\u00e0 kh\u00f3a m\u00e0 kh\u00f4ng c\u00f2n b\u1ed1i r\u1ed1i. 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Hi\u1ec3u r\u00f5 c\u00e1c th\u1ef1c th\u1ec3, m\u1ed1i quan h\u1ec7 v\u00e0 kh\u00f3a m\u00e0 kh\u00f4ng c\u00f2n b\u1ed1i r\u1ed1i. 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