{"id":1649,"date":"2026-04-06T16:34:57","date_gmt":"2026-04-06T16:34:57","guid":{"rendered":"https:\/\/www.viz-note.com\/vi\/foreign-keys-erd-performance-analysis\/"},"modified":"2026-04-06T16:34:57","modified_gmt":"2026-04-06T16:34:57","slug":"foreign-keys-erd-performance-analysis","status":"publish","type":"post","link":"https:\/\/www.viz-note.com\/vi\/foreign-keys-erd-performance-analysis\/","title":{"rendered":"Ph\u00e2n t\u00edch c\u1ea5u th\u00e0nh: C\u00e1ch c\u00e1c kh\u00f3a ngo\u1ea1i th\u1ef1c s\u1ef1 \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn hi\u1ec7u su\u1ea5t s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3"},"content":{"rendered":"

Khi c\u00e1c ki\u1ebfn tr\u00fac s\u01b0 thi\u1ebft k\u1ebf m\u00f4 h\u00ecnh d\u1eef li\u1ec7u, s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 (ERD) \u0111\u00f3ng vai tr\u00f2 l\u00e0 b\u1ea3n v\u1ebd n\u1ec1n t\u1ea3ng. N\u00f3 kh\u00f4ng ch\u1ec9 \u0111\u01a1n thu\u1ea7n l\u00e0 m\u1ed9t bi\u1ec3u di\u1ec5n tr\u1ef1c quan v\u1ec1 c\u00e1c b\u1ea3ng v\u00e0 c\u1ed9t; m\u00e0 c\u00f2n l\u00e0 m\u1ed9t b\u1ea3n m\u00f4 t\u1ea3 v\u1ec1 c\u00e1c m\u1ed1i quan h\u1ec7, t\u00ednh to\u00e0n v\u1eb9n v\u00e0 lu\u1ed3ng d\u1eef li\u1ec7u. Trong s\u1ed1 nh\u1eefng th\u00e0nh ph\u1ea7n quan tr\u1ecdng nh\u1ea5t trong c\u1ea5u tr\u00fac n\u00e0y l\u00e0 c\u00e1c kh\u00f3a ngo\u1ea1i. M\u1eb7c d\u00f9 th\u01b0\u1eddng \u0111\u01b0\u1ee3c li\u00ean k\u1ebft ch\u1ec9 v\u1edbi t\u00ednh to\u00e0n v\u1eb9n d\u1eef li\u1ec7u, nh\u01b0ng \u1ea3nh h\u01b0\u1edfng c\u1ee7a ch\u00fang c\u00f2n lan r\u1ed9ng s\u00e2u s\u1eafc \u0111\u1ebfn c\u00e1c ch\u1ec9 s\u1ed1 hi\u1ec7u su\u1ea5t, hi\u1ec7u qu\u1ea3 l\u01b0u tr\u1eef v\u00e0 t\u1ed1c \u0111\u1ed9 th\u1ef1c thi truy v\u1ea5n.<\/p>\n

Ph\u00e2n t\u00edch n\u00e0y kh\u00e1m ph\u00e1 c\u00e1c c\u01a1 ch\u1ebf k\u1ef9 thu\u1eadt c\u1ee7a c\u00e1c kh\u00f3a ngo\u1ea1i trong b\u1ed1i c\u1ea3nh hi\u1ec7u su\u1ea5t ERD. Ch\u00fang ta s\u1ebd xem x\u00e9t c\u00e1ch c\u00e1c r\u00e0ng bu\u1ed9c n\u00e0y \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn chi\u1ebfn l\u01b0\u1ee3c l\u1eadp ch\u1ec9 m\u1ee5c, c\u01a1 ch\u1ebf kh\u00f3a v\u00e0 kh\u1ea3 n\u0103ng m\u1edf r\u1ed9ng t\u1ed5ng th\u1ec3 c\u1ee7a l\u01b0\u1ee3c \u0111\u1ed3 c\u01a1 s\u1edf d\u1eef li\u1ec7u. M\u1ee5c ti\u00eau l\u00e0 cung c\u1ea5p s\u1ef1 hi\u1ec3u bi\u1ebft r\u00f5 r\u00e0ng v\u1ec1 nh\u1eefng th\u1ecfa hi\u1ec7p x\u1ea3y ra khi \u0111\u1ecbnh ngh\u0129a c\u00e1c m\u1ed1i quan h\u1ec7 trong m\u00f4 h\u00ecnh v\u1eadt l\u00fd.<\/p>\n

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

Hi\u1ec3u r\u00f5 ch\u1ee9c n\u0103ng c\u1ed1t l\u00f5i c\u1ee7a c\u00e1c kh\u00f3a ngo\u1ea1i \u2699\ufe0f<\/h2>\n

Kh\u00f3a ngo\u1ea1i l\u00e0 m\u1ed9t r\u00e0ng bu\u1ed9c li\u00ean k\u1ebft m\u1ed9t c\u1ed9t trong m\u1ed9t b\u1ea3ng v\u1edbi kh\u00f3a ch\u00ednh c\u1ee7a b\u1ea3ng kh\u00e1c. S\u1ef1 li\u00ean k\u1ebft n\u00e0y \u0111\u1ea3m b\u1ea3o t\u00ednh to\u00e0n v\u1eb9n tham chi\u1ebfu, \u0111\u1ea3m b\u1ea3o r\u1eb1ng m\u1ed9t b\u1ea3n ghi trong b\u1ea3ng con t\u01b0\u01a1ng \u1ee9ng v\u1edbi m\u1ed9t b\u1ea3n ghi t\u1ed3n t\u1ea1i trong b\u1ea3ng cha. Tuy nhi\u00ean, vi\u1ec7c tri\u1ec3n khai r\u00e0ng bu\u1ed9c n\u00e0y mang l\u1ea1i chi ph\u00ed t\u00ednh to\u00e1n.<\/p>\n

T\u1eeb g\u00f3c \u0111\u1ed9 hi\u1ec7u su\u1ea5t, kh\u00f3a ngo\u1ea1i \u0111\u00f3ng vai tr\u00f2 nh\u01b0 m\u1ed9t t\u00edn hi\u1ec7u g\u1eedi \u0111\u1ebfn b\u1ed9 x\u1eed l\u00fd c\u01a1 s\u1edf d\u1eef li\u1ec7u. N\u00f3 th\u00f4ng b\u00e1o cho b\u1ed9 l\u1eadp k\u1ebf ho\u1ea1ch truy v\u1ea5n v\u1ec1 s\u1ef1 t\u1ed3n t\u1ea1i c\u1ee7a m\u1ed1i quan h\u1ec7, \u0111i\u1ec1u n\u00e0y c\u00f3 th\u1ec3 \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn c\u00e1c thu\u1eadt to\u00e1n n\u1ed1i. Tuy nhi\u00ean, n\u00f3 c\u0169ng t\u1ea1o ra chi ph\u00ed b\u1ed5 sung trong qu\u00e1 tr\u00ecnh thao t\u00e1c d\u1eef li\u1ec7u.<\/p>\n

    \n
  • Thao t\u00e1c ch\u00e8n:<\/strong> Khi m\u1ed9t h\u00e0ng m\u1edbi \u0111\u01b0\u1ee3c th\u00eam v\u00e0o b\u1ea3ng con, b\u1ed9 x\u1eed l\u00fd ph\u1ea3i x\u00e1c minh xem kh\u00f3a cha \u0111\u01b0\u1ee3c tham chi\u1ebfu c\u00f3 t\u1ed3n t\u1ea1i hay kh\u00f4ng.<\/li>\n
  • Thao t\u00e1c x\u00f3a:<\/strong> Vi\u1ec7c x\u00f3a m\u1ed9t h\u00e0ng kh\u1ecfi b\u1ea3ng cha c\u00f3 th\u1ec3 y\u00eau c\u1ea7u c\u1eadp nh\u1eadt lan truy\u1ec1n ho\u1eb7c ki\u1ec3m tra c\u00e1c b\u1ea3n ghi con ph\u1ee5 thu\u1ed9c.<\/li>\n
  • Thao t\u00e1c c\u1eadp nh\u1eadt:<\/strong> Vi\u1ec7c thay \u0111\u1ed5i kh\u00f3a ch\u00ednh trong b\u1ea3ng cha bu\u1ed9c ph\u1ea3i c\u1eadp nh\u1eadt m\u1ecdi tham chi\u1ebfu kh\u00f3a ngo\u1ea1i trong c\u00e1c b\u1ea3ng con.<\/li>\n<\/ul>\n

    Nh\u1eefng ki\u1ec3m tra n\u00e0y kh\u00f4ng di\u1ec5n ra t\u1ee9c th\u00ec. Ch\u00fang \u0111\u00f2i h\u1ecfi c\u01a1 ch\u1ebf kh\u00f3a \u0111\u1ec3 ng\u0103n ch\u1eb7n c\u00e1c t\u00ecnh hu\u1ed1ng c\u1ea1nh tranh khi hai giao d\u1ecbch c\u00f9ng c\u1ed1 g\u1eafng thay \u0111\u1ed5i d\u1eef li\u1ec7u li\u00ean quan m\u1ed9t c\u00e1ch \u0111\u1ed3ng th\u1eddi. Do \u0111\u00f3, m\u1eadt \u0111\u1ed9 c\u00e1c kh\u00f3a ngo\u1ea1i trong ERD t\u1ef7 l\u1ec7 tr\u1ef1c ti\u1ebfp v\u1edbi \u0111\u1ed9 ph\u1ee9c t\u1ea1p c\u1ee7a qu\u1ea3n l\u00fd giao d\u1ecbch.<\/p>\n

    Ch\u1ec9 s\u1ed1 hi\u1ec7u su\u1ea5t: T\u1ea3i \u0111\u1ecdc so v\u1edbi t\u1ea3i ghi \ud83d\udcca<\/h2>\n

    Hi\u1ec7u su\u1ea5t c\u01a1 s\u1edf d\u1eef li\u1ec7u hi\u1ebfm khi \u0111\u1ed3ng \u0111\u1ec1u tr\u00ean t\u1ea5t c\u1ea3 c\u00e1c thao t\u00e1c. C\u00e1c kh\u00f3a ngo\u1ea1i \u1ea3nh h\u01b0\u1edfng kh\u00e1c nhau \u0111\u1ebfn t\u1ea3i \u0111\u1ecdc v\u00e0 t\u1ea3i ghi. Hi\u1ec3u r\u00f5 s\u1ef1 kh\u00e1c bi\u1ec7t n\u00e0y l\u00e0 \u0111i\u1ec1u c\u1ea7n thi\u1ebft \u0111\u1ec3 t\u1ed1i \u01b0u h\u00f3a thi\u1ebft k\u1ebf l\u01b0\u1ee3c \u0111\u1ed3.<\/p>\n

    1. Hi\u1ec7u su\u1ea5t \u0111\u1ecdc (Th\u1ef1c thi truy v\u1ea5n)<\/h3>\n

    Khi m\u1ed9t truy v\u1ea5n bao g\u1ed3m vi\u1ec7c n\u1ed1i hai b\u1ea3ng, s\u1ef1 hi\u1ec7n di\u1ec7n c\u1ee7a m\u1ed1i quan h\u1ec7 kh\u00f3a ngo\u1ea1i c\u00f3 th\u1ec3 h\u1ed7 tr\u1ee3 b\u1ed9 t\u1ed1i \u01b0u h\u00f3a. N\u1ebfu th\u1ed1ng k\u00ea \u0111\u01b0\u1ee3c duy tr\u00ec, b\u1ed9 x\u1eed l\u00fd c\u00f3 th\u1ec3 \u01b0\u1edbc l\u01b0\u1ee3ng ch\u00ednh x\u00e1c h\u01a1n \u0111\u1ed9 cardinality c\u1ee7a ph\u00e9p n\u1ed1i. \u0110i\u1ec1u n\u00e0y th\u01b0\u1eddng d\u1eabn \u0111\u1ebfn c\u00e1c k\u1ebf ho\u1ea1ch th\u1ef1c thi t\u1ed1t h\u01a1n.<\/p>\n

      \n
    • T\u1ed1i \u01b0u h\u00f3a n\u1ed1i:<\/strong> B\u1ed9 l\u1eadp k\u1ebf ho\u1ea1ch truy v\u1ea5n c\u00f3 th\u1ec3 ch\u1ecdn n\u1ed1i ki\u1ec3u hash ho\u1eb7c n\u1ed1i ki\u1ec3u h\u1ee3p nh\u1ea5t d\u1ef1a tr\u00ean c\u00e1c r\u00e0ng bu\u1ed9c \u0111\u1ed9 cardinality \u0111\u00e3 bi\u1ebft.<\/li>\n
    • S\u1eed d\u1ee5ng ch\u1ec9 m\u1ee5c:<\/strong>C\u00e1c kh\u00f3a ngo\u1ea1i th\u01b0\u1eddng th\u00fac \u0111\u1ea9y vi\u1ec7c t\u1ea1o ch\u1ec9 m\u1ee5c tr\u00ean c\u00e1c c\u1ed9t b\u1ea3ng con. Nh\u1eefng ch\u1ec9 m\u1ee5c n\u00e0y l\u00e0m t\u0103ng t\u1ed1c \u0111\u1ed9 t\u00ecm ki\u1ebfm trong qu\u00e1 tr\u00ecnh n\u1ed1i.<\/li>\n
    • Hi\u1ec7u qu\u1ea3 b\u1ed9 nh\u1edb \u0111\u1ec7m:<\/strong>C\u00e1c kh\u00f3a ngo\u1ea1i \u0111\u01b0\u1ee3c ch\u1ec9 m\u1ee5c h\u1ee3p l\u00fd cho ph\u00e9p \u0111\u1ecdc trang hi\u1ec7u qu\u1ea3 h\u01a1n t\u1eeb b\u1ed9 nh\u1edb, gi\u1ea3m thi\u1ec3u I\/O \u0111\u0129a.<\/li>\n<\/ul>\n

      2. Hi\u1ec7u su\u1ea5t ghi (Thao t\u00e1c d\u1eef li\u1ec7u)<\/h3>\n

      Vi\u1ec7c ghi l\u00e0 n\u01a1i c\u00e1c kh\u00f3a ngo\u1ea1i t\u1ea1o ra \u0111\u1ed9 tr\u1ec5 \u0111\u00e1ng k\u1ec3. M\u1ecdi thao t\u00e1c ch\u00e8n ho\u1eb7c c\u1eadp nh\u1eadt \u0111\u1ec1u ph\u1ea3i x\u00e1c th\u1ef1c r\u00e0ng bu\u1ed9c.<\/p>\n

        \n
      • Chi ph\u00ed tra c\u1ee9u:<\/strong>H\u1ec7 th\u1ed1ng ph\u1ea3i t\u00ecm ki\u1ebfm ch\u1ec9 m\u1ee5c b\u1ea3ng cha \u0111\u1ec3 x\u00e1c nh\u1eadn kh\u00f3a t\u1ed3n t\u1ea1i. \u0110i\u1ec1u n\u00e0y th\u00eam m\u1ed9t thao t\u00e1c \u0111\u1ecdc v\u00e0o m\u1ed7i thao t\u00e1c ghi.<\/li>\n
      • Chi ph\u00ed lan truy\u1ec1n:<\/strong> N\u1ebfu ch\u1ee9c n\u0103ng x\u00f3a ho\u1eb7c c\u1eadp nh\u1eadt lan truy\u1ec1n \u0111\u01b0\u1ee3c b\u1eadt, m\u1ed9t thao t\u00e1c duy nh\u1ea5t tr\u00ean b\u1ea3n ghi cha c\u00f3 th\u1ec3 k\u00edch ho\u1ea1t c\u00e1c c\u1eadp nh\u1eadt tr\u00ean nhi\u1ec1u b\u1ea3ng con.<\/li>\n
      • Xung \u0111\u1ed9t kh\u00f3a:<\/strong> C\u00e1c kh\u00f3a ngo\u1ea1i t\u1ea1o ra c\u00e1c ph\u1ee5 thu\u1ed9c gi\u1eefa c\u00e1c h\u00e0ng. N\u1ebfu hai giao d\u1ecbch c\u00f9ng c\u1ed1 g\u1eafng ch\u00e8n v\u00e0o c\u00f9ng m\u1ed9t h\u00e0ng cha, ch\u00fang c\u00f3 th\u1ec3 ch\u1eb7n l\u1eabn nhau trong khi ch\u1edd ki\u1ec3m tra t\u00ednh to\u00e0n v\u1eb9n ho\u00e0n t\u1ea5t.<\/li>\n<\/ul>\n

        M\u1ed1i quan h\u1ec7 l\u1eadp ch\u1ec9 m\u1ee5c \ud83d\udd17<\/h2>\n

        M\u1ed9t trong nh\u1eefng hi\u1ec3u l\u1ea7m ph\u1ed5 bi\u1ebfn nh\u1ea5t l\u00e0 c\u00e1c kh\u00f3a ngo\u1ea1i t\u1ef1 \u0111\u1ed9ng t\u1ea1o ch\u1ec9 m\u1ee5c. \u1ede nhi\u1ec1u h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u, \u0111\u00e2y kh\u00f4ng ph\u1ea3i l\u00e0 h\u00e0nh vi m\u1eb7c \u0111\u1ecbnh. Tuy nhi\u00ean, d\u1ef1a v\u00e0o kh\u00f3a ngo\u1ea1i m\u00e0 kh\u00f4ng c\u00f3 ch\u1ec9 m\u1ee5c tr\u00ean c\u1ed9t con s\u1ebd tr\u1edf th\u00e0nh \u0111i\u1ec3m ngh\u1ebdn hi\u1ec7u su\u1ea5t.<\/p>\n

        Kh\u00f4ng c\u00f3 ch\u1ec9 m\u1ee5c tr\u00ean c\u1ed9t kh\u00f3a ngo\u1ea1i:<\/p>\n

          \n
        • C\u01a1 s\u1edf d\u1eef li\u1ec7u ph\u1ea3i th\u1ef1c hi\u1ec7n qu\u00e9t to\u00e0n b\u1ed9 b\u1ea3ng \u0111\u1ec3 x\u00e1c minh s\u1ef1 t\u1ed3n t\u1ea1i c\u1ee7a kh\u00f3a cha trong qu\u00e1 tr\u00ecnh ch\u00e8n d\u1eef li\u1ec7u.<\/li>\n
        • C\u00e1c thao t\u00e1c n\u1ed1i gi\u1eefa b\u1ea3ng cha v\u00e0 b\u1ea3ng con s\u1ebd ch\u1eadm \u0111\u00e1ng k\u1ec3, th\u01b0\u1eddng ph\u1ea3i s\u1eed d\u1ee5ng c\u00e1c ph\u00e9p n\u1ed1i v\u00f2ng l\u1eb7p l\u1ed3ng nhau.<\/li>\n
        • C\u00e1c ki\u1ec3m tra t\u00ednh to\u00e0n v\u1eb9n tham chi\u1ebfu tr\u1edf n\u00ean t\u1ed1n k\u00e9m khi d\u1eef li\u1ec7u ng\u00e0y c\u00e0ng l\u1edbn.<\/li>\n<\/ul>\n

          Ng\u01b0\u1ee3c l\u1ea1i, vi\u1ec7c th\u00eam ch\u1ec9 m\u1ee5c v\u00e0o c\u1ed9t kh\u00f3a ngo\u1ea1i gi\u1ea3i quy\u1ebft c\u00e1c v\u1ea5n \u0111\u1ec1 n\u00e0y nh\u01b0ng l\u1ea1i mang l\u1ea1i chi ph\u00ed ri\u00eang:<\/p>\n

            \n
          • Chi ph\u00ed l\u01b0u tr\u1eef:<\/strong> M\u1ed7i ch\u1ec9 m\u1ee5c ti\u00eau t\u1ed1n kh\u00f4ng gian \u0111\u0129a v\u00e0 b\u1ed9 nh\u1edb.<\/li>\n
          • T\u1ed1c \u0111\u1ed9 ghi ch\u1eadm l\u1ea1i:<\/strong> M\u1ed7i l\u1ea7n m\u1ed9t h\u00e0ng \u0111\u01b0\u1ee3c ch\u00e8n, c\u1eadp nh\u1eadt ho\u1eb7c x\u00f3a, ch\u1ec9 m\u1ee5c ph\u1ea3i \u0111\u01b0\u1ee3c s\u1eeda \u0111\u1ed5i.<\/li>\n
          • Ph\u00e2n m\u1ea3nh:<\/strong> Theo th\u1eddi gian, c\u00e1c ch\u1ec9 m\u1ee5c c\u00f3 th\u1ec3 tr\u1edf n\u00ean ph\u00e2n m\u1ea3nh, \u0111\u00f2i h\u1ecfi c\u00e1c thao t\u00e1c b\u1ea3o tr\u00ec.<\/li>\n<\/ul>\n

            B\u1ea3ng: T\u00e1c \u0111\u1ed9ng c\u1ee7a vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c kh\u00f3a ngo\u1ea1i<\/h3>\n\n\n\n\n\n\n\n\n
            Y\u1ebfu t\u1ed1<\/th>\nKh\u00f4ng c\u00f3 ch\u1ec9 m\u1ee5c kh\u00f3a ngo\u1ea1i<\/th>\nC\u00f3 ch\u1ec9 m\u1ee5c kh\u00f3a ngo\u1ea1i<\/th>\n<\/tr>\n<\/thead>\n
            T\u1ed1c \u0111\u1ed9 ch\u00e8n<\/strong><\/td>\nCh\u1eadm h\u01a1n (ki\u1ec3m tra qu\u00e9t to\u00e0n b\u1ed9)<\/td>\nNhanh h\u01a1n (tra c\u1ee9u ch\u1ec9 m\u1ee5c)<\/td>\n<\/tr>\n
            T\u1ed1c \u0111\u1ed9 n\u1ed1i<\/strong><\/td>\nCh\u1eadm (v\u00f2ng l\u1eb7p l\u1ed3ng nhau)<\/td>\nNhanh (n\u1ed1i b\u0103m\/gh\u00e9p)<\/td>\n<\/tr>\n
            S\u1eed d\u1ee5ng b\u1ed9 nh\u1edb<\/strong><\/td>\nTh\u1ea5p<\/td>\nCao h\u01a1n<\/td>\n<\/tr>\n
            Chi ph\u00ed c\u1eadp nh\u1eadt<\/strong><\/td>\nTh\u1ea5p<\/td>\nCao (b\u1ea3o tr\u00ec ch\u1ec9 m\u1ee5c)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

            Tr\u1ef1c quan h\u00f3a ERD v\u00e0 \u0111\u1ed9 ph\u1ee9c t\u1ea1p \ud83c\udfa8<\/h2>\n

            ERD l\u00e0 m\u1ed9t c\u00f4ng c\u1ee5 giao ti\u1ebfp gi\u1eefa c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n, ki\u1ebfn tr\u00fac s\u01b0 v\u00e0 c\u00e1c b\u00ean li\u00ean quan. M\u1eadt \u0111\u1ed9 c\u00e1c kh\u00f3a ngo\u1ea1i \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn \u0111\u1ed9 d\u1ec5 \u0111\u1ecdc c\u1ee7a s\u01a1 \u0111\u1ed3. M\u1ed9t s\u01a1 \u0111\u1ed3 b\u1ecb r\u1ed1i r\u1eafm b\u1edfi qu\u00e1 nhi\u1ec1u m\u1ed1i quan h\u1ec7 c\u00f3 th\u1ec3 che khu\u1ea5t lu\u1ed3ng d\u1eef li\u1ec7u ch\u00ednh.<\/p>\n

            1. R\u1ed1i m\u1eaft v\u1ec1 m\u1eb7t tr\u1ef1c quan<\/h3>\n

            Khi m\u1ed9t th\u1ef1c th\u1ec3 c\u00f3 nhi\u1ec1u kh\u00f3a ngo\u1ea1i ra ho\u1eb7c v\u00e0o, c\u00e1c \u0111\u01b0\u1eddng n\u1ed1i ch\u00fang t\u1ea1o hi\u1ec7u \u1ee9ng ‘s\u01a1 \u0111\u1ed3 m\u00ec \u0103n li\u1ec1n’. \u0110i\u1ec1u n\u00e0y khi\u1ebfn vi\u1ec7c theo d\u00f5i ngu\u1ed3n g\u1ed1c d\u1eef li\u1ec7u ho\u1eb7c hi\u1ec3u c\u00e1c m\u1ed1i quan h\u1ec7 c\u1ed1t l\u00f5i c\u1ee7a m\u1ed9t th\u1ef1c th\u1ec3 c\u1ee5 th\u1ec3 tr\u1edf n\u00ean kh\u00f3 kh\u0103n.<\/p>\n

              \n
            • C\u00e1c \u0111\u01b0\u1eddng ch\u00e9o nhau:<\/strong> Qu\u00e1 nhi\u1ec1u m\u1ed1i quan h\u1ec7 khi\u1ebfn c\u00e1c \u0111\u01b0\u1eddng ch\u00e9o nhau, l\u00e0m gi\u1ea3m \u0111\u1ed9 r\u00f5 r\u00e0ng.<\/li>\n
            • K\u00edch th\u01b0\u1edbc n\u00fat:<\/strong> C\u00e1c th\u1ef1c th\u1ec3 c\u00f3 s\u1ed1 l\u01b0\u1ee3ng m\u1ed1i quan h\u1ec7 cao c\u1ea7n c\u00e1c h\u1ed9p bao l\u1edbn h\u01a1n, l\u00e0m m\u1ea5t c\u00e2n \u0111\u1ed1i \u0111\u1ed1i x\u1ee9ng b\u1ed1 c\u1ee5c.<\/li>\n
            • Th\u1eddi gian di\u1ec5n gi\u1ea3i:<\/strong> C\u00e1c k\u1ef9 s\u01b0 d\u00e0nh nhi\u1ec1u th\u1eddi gian gi\u1ea3i m\u00e3 m\u00f4 h\u00ecnh h\u01a1n l\u00e0 tri\u1ec3n khai logic.<\/li>\n<\/ul>\n

              2. M\u00f4 h\u00ecnh logic so v\u1edbi m\u00f4 h\u00ecnh v\u1eadt l\u00fd<\/h3>\n

              Th\u01b0\u1eddng xuy\u00ean c\u1ea7n ph\u00e2n bi\u1ec7t gi\u1eefa ERD logic v\u00e0 s\u01a1 \u0111\u1ed3 v\u1eadt l\u00fd. M\u00f4 h\u00ecnh logic t\u1eadp trung v\u00e0o c\u00e1c quy t\u1eafc kinh doanh v\u00e0 m\u1ed1i quan h\u1ec7. M\u00f4 h\u00ecnh v\u1eadt l\u00fd t\u1eadp trung v\u00e0o hi\u1ec7u su\u1ea5t v\u00e0 tri\u1ec3n khai.<\/p>\n

                \n
              • M\u1ee9c \u0111\u1ed9 logic:<\/strong>T\u1ea5t c\u1ea3 c\u00e1c m\u1ed1i quan h\u1ec7 c\u1ea7n \u0111\u01b0\u1ee3c bi\u1ec3u di\u1ec5n \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o c\u00e1c quy t\u1eafc kinh doanh \u0111\u01b0\u1ee3c ghi nh\u1eadn.<\/li>\n
              • M\u1ee9c \u0111\u1ed9 v\u1eadt l\u00fd:<\/strong>M\u1ed9t s\u1ed1 m\u1ed1i quan h\u1ec7 c\u00f3 th\u1ec3 b\u1ecb lo\u1ea1i b\u1ecf ho\u1eb7c kh\u00f4ng chu\u1ea9n h\u00f3a \u0111\u1ec3 c\u1ea3i thi\u1ec7n t\u1ed1c \u0111\u1ed9 truy v\u1ea5n.<\/li>\n<\/ul>\n

                S\u1ef1 ph\u00e2n t\u00e1ch n\u00e0y cho ph\u00e9p ERD v\u1eabn l\u00e0 m\u1ed9t t\u00e0i li\u1ec7u kinh doanh h\u1ee3p l\u1ec7 trong khi c\u01a1 s\u1edf d\u1eef li\u1ec7u n\u1ec1n t\u1ea3ng \u0111\u01b0\u1ee3c t\u1ed1i \u01b0u h\u00f3a cho c\u00e1c m\u1eabu c\u00f4ng vi\u1ec7c c\u1ee5 th\u1ec3.<\/p>\n

                Chu\u1ea9n h\u00f3a v\u00e0 s\u1ef1 c\u00e2n b\u1eb1ng gi\u1eefa c\u00e1c kh\u00f3a ngo\u1ea1i \u2696\ufe0f<\/h2>\n

                Vi\u1ec7c quy\u1ebft \u0111\u1ecbnh chu\u1ea9n h\u00f3a c\u01a1 s\u1edf d\u1eef li\u1ec7u bao g\u1ed3m vi\u1ec7c gi\u1edbi thi\u1ec7u c\u00e1c kh\u00f3a ngo\u1ea1i. Chu\u1ea9n h\u00f3a gi\u1ea3m thi\u1ec3u s\u1ef1 tr\u00f9ng l\u1eb7p v\u00e0 \u0111\u1ea3m b\u1ea3o t\u00ednh nh\u1ea5t qu\u00e1n d\u1eef li\u1ec7u. Tuy nhi\u00ean, n\u00f3 l\u00e0m t\u0103ng s\u1ed1 l\u01b0\u1ee3ng ph\u00e9p n\u1ed1i c\u1ea7n thi\u1ebft \u0111\u1ec3 truy xu\u1ea5t d\u1eef li\u1ec7u.<\/p>\n

                D\u1ea1ng chu\u1ea9n h\u00f3a th\u1ee9 ba (3NF)<\/h3>\n

                Trong 3NF, m\u1ecdi thu\u1ed9c t\u00ednh kh\u00f4ng kh\u00f3a \u0111\u1ec1u ph\u1ee5 thu\u1ed9c v\u00e0o to\u00e0n b\u1ed9 kh\u00f3a. \u0110i\u1ec1u n\u00e0y d\u1eabn \u0111\u1ebfn m\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 c\u00f3 nhi\u1ec1u b\u1ea3ng v\u00e0 nhi\u1ec1u kh\u00f3a ngo\u1ea1i.<\/p>\n

                  \n
                • \u01afu \u0111i\u1ec3m:<\/strong>T\u1ed1i thi\u1ec3u h\u00f3a tr\u00f9ng l\u1eb7p d\u1eef li\u1ec7u, c\u1eadp nh\u1eadt nh\u1ea5t qu\u00e1n, l\u01b0u tr\u1eef th\u1ea5p h\u01a1n cho c\u00e1c tr\u01b0\u1eddng v\u0103n b\u1ea3n.<\/li>\n
                • Nh\u01b0\u1ee3c \u0111i\u1ec3m:<\/strong>Truy v\u1ea5n ph\u1ee9c t\u1ea1p y\u00eau c\u1ea7u nhi\u1ec1u ph\u00e9p n\u1ed1i, nguy c\u01a1 suy gi\u1ea3m hi\u1ec7u su\u1ea5t tr\u00ean c\u00e1c h\u1ec7 th\u1ed1ng \u0111\u1ecdc d\u1eef li\u1ec7u nhi\u1ec1u.<\/li>\n<\/ul>\n

                  Chi\u1ebfn l\u01b0\u1ee3c kh\u00f4ng chu\u1ea9n h\u00f3a<\/h3>\n

                  \u0110\u1ed1i v\u1edbi c\u00e1c \u1ee9ng d\u1ee5ng b\u00e1o c\u00e1o hi\u1ec7u su\u1ea5t cao ho\u1eb7c c\u00e1c h\u1ec7 th\u1ed1ng \u0111\u1ecdc d\u1eef li\u1ec7u nhi\u1ec1u, kh\u00f4ng chu\u1ea9n h\u00f3a l\u00e0 m\u1ed9t chi\u1ebfn l\u01b0\u1ee3c kh\u1ea3 thi. \u0110i\u1ec1u n\u00e0y bao g\u1ed3m vi\u1ec7c lo\u1ea1i b\u1ecf c\u00e1c kh\u00f3a ngo\u1ea1i v\u00e0 nh\u00e2n b\u1ea3n d\u1eef li\u1ec7u.<\/p>\n

                    \n
                  • C\u00e1c view \u0111\u00e3 \u0111\u01b0\u1ee3c v\u1eadt ch\u1ea5t h\u00f3a:<\/strong>K\u1ebft qu\u1ea3 \u0111\u00e3 \u0111\u01b0\u1ee3c t\u00ednh to\u00e1n tr\u01b0\u1edbc v\u00e0 l\u01b0u tr\u1eef d\u01b0\u1edbi d\u1ea1ng b\u1ea3ng gi\u1ea3m nhu c\u1ea7u v\u1ec1 c\u00e1c ph\u00e9p n\u1ed1i.<\/li>\n
                  • C\u00e1c c\u1ed9t d\u01b0 th\u1eeba:<\/strong> L\u01b0u t\u00ean m\u1ed9t danh m\u1ee5c tr\u1ef1c ti\u1ebfp trong b\u1ea3ng giao d\u1ecbch tr\u00e1nh \u0111\u01b0\u1ee3c vi\u1ec7c k\u1ebft n\u1ed1i \u0111\u1ebfn b\u1ea3ng danh m\u1ee5c.<\/li>\n
                  • S\u1ef1 \u0111\u00e1nh \u0111\u1ed5i:<\/strong>B\u1ea1n hy sinh hi\u1ec7u su\u1ea5t ghi v\u00e0 t\u0103ng dung l\u01b0\u1ee3ng l\u01b0u tr\u1eef \u0111\u1ec3 \u0111\u1ea1t \u0111\u01b0\u1ee3c t\u1ed1c \u0111\u1ed9 \u0111\u1ecdc nhanh h\u01a1n.<\/li>\n<\/ul>\n

                    B\u1ea3ng: Chu\u1ea9n h\u00f3a so v\u1edbi Hi\u1ec7u su\u1ea5t<\/h3>\n\n\n\n\n\n\n\n\n
                    Kh\u00eda c\u1ea1nh<\/th>\nChu\u1ea9n h\u00f3a (Nhi\u1ec1u kh\u00f3a ngo\u1ea1i)<\/th>\nKh\u00f4ng chu\u1ea9n h\u00f3a (\u00cdt kh\u00f3a ngo\u1ea1i)<\/th>\n<\/tr>\n<\/thead>\n
                    \u0110\u1ed9 to\u00e0n v\u1eb9n d\u1eef li\u1ec7u<\/strong><\/td>\nCao (\u0110\u01b0\u1ee3c \u0111\u1ea3m b\u1ea3o b\u1edfi kh\u00f3a ngo\u1ea1i)<\/td>\nTh\u1ea5p (C\u1ea7n ki\u1ec3m tra th\u1ee7 c\u00f4ng)<\/td>\n<\/tr>\n
                    \u0110\u1ed9 ph\u1ee9c t\u1ea1p truy v\u1ea5n<\/strong><\/td>\nCao (Nhi\u1ec1u ph\u00e9p n\u1ed1i)<\/td>\nTh\u1ea5p (M\u1ed9t b\u1ea3ng duy nh\u1ea5t)<\/td>\n<\/tr>\n
                    T\u1ed1c \u0111\u1ed9 ghi<\/strong><\/td>\nNhanh h\u01a1n (\u00cdt tr\u00f9ng l\u1eb7p h\u01a1n)<\/td>\nCh\u1eadm h\u01a1n (C\u1eadp nh\u1eadt t\u1ea5t c\u1ea3 b\u1ea3n sao)<\/td>\n<\/tr>\n
                    T\u1ed1c \u0111\u1ed9 \u0111\u1ecdc<\/strong><\/td>\nCh\u1eadm h\u01a1n<\/td>\nNhanh h\u01a1n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

                    C\u01a1 ch\u1ebf \u0111\u1ed3ng th\u1eddi v\u00e0 kh\u00f3a \ud83d\udd12<\/h2>\n

                    Kh\u00f3a ngo\u1ea1i t\u1ea1o ra m\u1ed9t lo\u1ea1i h\u00e0nh vi kh\u00f3a c\u1ee5 th\u1ec3 \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 kh\u00f3a \u0111i\u1ec1u ki\u1ec7n ho\u1eb7c kh\u00f3a kho\u1ea3ng tr\u1ed1ng trong m\u1ed9t s\u1ed1 h\u1ec7 qu\u1ea3n tr\u1ecb c\u01a1 s\u1edf d\u1eef li\u1ec7u. Khi m\u1ed9t giao d\u1ecbch thay \u0111\u1ed5i m\u1ed9t h\u00e0ng \u0111\u01b0\u1ee3c tham chi\u1ebfu b\u1edfi kh\u00f3a ngo\u1ea1i, n\u00f3 ph\u1ea3i kh\u00f3a kh\u00f4ng ch\u1ec9 h\u00e0ng \u0111ang \u0111\u01b0\u1ee3c thay \u0111\u1ed5i m\u00e0 c\u00f2n c\u00f3 th\u1ec3 ph\u1ea3i kh\u00f3a h\u00e0ng cha t\u01b0\u01a1ng \u1ee9ng.<\/p>\n

                    1. Ch\u1ebft ch\u1eb7n<\/h3>\n

                    C\u00e1c l\u01b0\u1ee3c \u0111\u1ed3 c\u00f3 k\u1ebft n\u1ed1i cao v\u1edbi nhi\u1ec1u kh\u00f3a ngo\u1ea1i d\u1ec5 b\u1ecb ch\u1ebft ch\u1eb7n. \u0110i\u1ec1u n\u00e0y x\u1ea3y ra khi hai giao d\u1ecbch c\u00f9ng gi\u1eef kh\u00f3a tr\u00ean c\u00e1c t\u00e0i nguy\u00ean m\u00e0 giao d\u1ecbch kia c\u1ea7n.<\/p>\n

                      \n
                    • T\u00ecnh hu\u1ed1ng:<\/strong> Giao d\u1ecbch A c\u1eadp nh\u1eadt b\u1ea3ng cha X. Giao d\u1ecbch B c\u1eadp nh\u1eadt b\u1ea3ng con Y tham chi\u1ebfu \u0111\u1ebfn X.<\/li>\n
                    • Xung \u0111\u1ed9t:<\/strong> N\u1ebfu c\u1ea3 hai giao d\u1ecbch c\u00f9ng c\u1ed1 g\u1eafng kh\u00f3a t\u00e0i nguy\u00ean c\u1ee7a nhau theo th\u1ee9 t\u1ef1 kh\u00e1c nhau, h\u1ec7 th\u1ed1ng s\u1ebd t\u1ea1m d\u1eebng c\u1ea3 hai.<\/li>\n<\/ul>\n

                      2. \u0110\u1ed9 chi ti\u1ebft<\/h3>\n

                      C\u00e1c \u0111\u1ed9ng c\u01a1 c\u01a1 s\u1edf d\u1eef li\u1ec7u th\u01b0\u1eddng kh\u00f3a \u1edf c\u1ea5p \u0111\u1ed9 h\u00e0ng. Tuy nhi\u00ean, c\u00e1c r\u00e0ng bu\u1ed9c kh\u00f3a ngo\u1ea1i c\u00f3 th\u1ec3 bu\u1ed9c ph\u1ea3i kh\u00f3a \u1edf c\u1ea5p \u0111\u1ed9 ch\u1ec9 m\u1ee5c. N\u1ebfu m\u1ed9t ch\u1ec9 m\u1ee5c \u0111\u01b0\u1ee3c qu\u00e9t \u0111\u1ec3 x\u00e1c minh kh\u00f3a ngo\u1ea1i, to\u00e0n b\u1ed9 ph\u1ea1m vi ch\u1ec9 m\u1ee5c c\u00f3 th\u1ec3 b\u1ecb kh\u00f3a.<\/p>\n

                        \n
                      • T\u00e1c \u0111\u1ed9ng:<\/strong> C\u00e1c h\u1ec7 th\u1ed1ng x\u1eed l\u00fd \u0111\u1ed3ng th\u1eddi cao c\u00f3 th\u1ec3 g\u1eb7p ph\u1ea3i gi\u1ea3m b\u0103ng th\u00f4ng n\u1ebfu ki\u1ec3m tra kh\u00f3a ngo\u1ea1i l\u00e0m ch\u1eb7n c\u00e1c giao d\u1ecbch kh\u00e1c.<\/li>\n
                      • Gi\u1ea3m thi\u1ec3u:<\/strong>S\u1eafp x\u1ebfp c\u1ea9n th\u1eadn th\u1ee9 t\u1ef1 c\u00e1c giao d\u1ecbch v\u00e0 \u0111\u1ea3m b\u1ea3o c\u00e1c ch\u1ec9 m\u1ee5c \u0111\u01b0\u1ee3c \u0111\u1ed3ng b\u1ed9 v\u1edbi m\u1eabu truy v\u1ea5n c\u00f3 th\u1ec3 gi\u1ea3m thi\u1ec3u xung \u0111\u1ed9t.<\/li>\n<\/ul>\n

                        Chi ph\u00ed l\u01b0u tr\u1eef v\u00e0 dung l\u01b0\u1ee3ng b\u1ed9 nh\u1edb \ud83d\udcbe<\/h2>\n

                        M\u1ed7i c\u1ed9t kh\u00f3a ngo\u1ea1i \u0111\u1ec1u ti\u00eau t\u1ed1n dung l\u01b0\u1ee3ng l\u01b0u tr\u1eef. M\u1eb7c d\u00f9 m\u1ed9t s\u1ed1 nguy\u00ean ho\u1eb7c UUID \u0111\u01a1n l\u1ebb c\u00f3 v\u1ebb nh\u1ecf, nh\u01b0ng trong h\u1ec7 th\u1ed1ng c\u00f3 h\u00e0ng t\u1ef7 b\u1ea3n ghi, \u0111i\u1ec1u n\u00e0y s\u1ebd t\u00edch l\u0169y l\u1ea1i.<\/p>\n

                        1. Ki\u1ec3u d\u1eef li\u1ec7u v\u00e0 s\u1ef1 \u0111\u1ed3ng b\u1ed9<\/h3>\n

                        Ki\u1ec3u d\u1eef li\u1ec7u c\u1ee7a kh\u00f3a ngo\u1ea1i ph\u1ea3i kh\u1edbp v\u1edbi kh\u00f3a ch\u00ednh. N\u1ebfu kh\u00f3a ch\u00ednh l\u00e0 kh\u00f3a h\u1ee3p th\u00e0nh (nhi\u1ec1u c\u1ed9t), th\u00ec kh\u00f3a ngo\u1ea1i c\u0169ng ph\u1ea3i l\u00e0 kh\u00f3a h\u1ee3p th\u00e0nh.<\/p>\n

                          \n
                        • Kh\u00f3a h\u1ee3p th\u00e0nh:<\/strong> Ch\u00fang l\u00e0m t\u0103ng \u0111\u00e1ng k\u1ec3 k\u00edch th\u01b0\u1edbc c\u1ee7a ch\u1ec9 m\u1ee5c. M\u1ed9t ch\u1ec9 m\u1ee5c kh\u00f3a ngo\u1ea1i h\u1ee3p th\u00e0nh c\u00f3 th\u1ec3 l\u1edbn h\u01a1n nhi\u1ec1u so v\u1edbi ch\u1ec9 m\u1ee5c c\u1ed9t \u0111\u01a1n.<\/li>\n
                        • Kh\u1ea3 n\u0103ng ch\u1ea5p nh\u1eadn gi\u00e1 tr\u1ecb null:<\/strong> N\u1ebfu kh\u00f3a ngo\u1ea1i cho ph\u00e9p gi\u00e1 tr\u1ecb null, b\u1ed9 qu\u1ea3n l\u00fd l\u01b0u tr\u1eef ph\u1ea3i x\u1eed l\u00fd b\u1ea3n \u0111\u1ed3 null, l\u00e0m t\u0103ng th\u00eam chi ph\u00ed nh\u1ecf.<\/li>\n<\/ul>\n

                          2. S\u1eed d\u1ee5ng b\u1ed9 nh\u1edb<\/h3>\n

                          C\u00e1c ch\u1ec9 m\u1ee5c \u0111\u01b0\u1ee3c l\u01b0u tr\u1eef trong b\u1ed9 nh\u1edb trong qu\u00e1 tr\u00ecnh th\u1ef1c thi truy v\u1ea5n. M\u1ed9t s\u1ed1 l\u01b0\u1ee3ng l\u1edbn kh\u00f3a ngo\u1ea1i c\u00f9ng v\u1edbi c\u00e1c ch\u1ec9 m\u1ee5c t\u01b0\u01a1ng \u1ee9ng c\u00f3 th\u1ec3 l\u00e0m c\u1ea1n ki\u1ec7t b\u1ed9 nh\u1edb \u0111\u1ec7m s\u1eb5n c\u00f3.<\/p>\n

                            \n
                          • L\u00e0m b\u1ea9n b\u1ed9 nh\u1edb \u0111\u1ec7m:<\/strong>D\u1eef li\u1ec7u th\u01b0\u1eddng xuy\u00ean truy c\u1eadp b\u1ecb \u0111\u1ea9y ra kh\u1ecfi b\u1ed9 nh\u1edb \u0111\u1ec3 nh\u01b0\u1eddng ch\u1ed7 cho c\u1ea5u tr\u00fac ch\u1ec9 m\u1ee5c.<\/li>\n
                          • S\u1eed d\u1ee5ng b\u1ed9 nh\u1edb \u1ea3o:<\/strong> N\u1ebfu b\u1ed9 nh\u1edb kh\u00f4ng \u0111\u1ee7, h\u1ec7 th\u1ed1ng c\u00f3 th\u1ec3 chuy\u1ec3n sang s\u1eed d\u1ee5ng b\u1ed9 nh\u1edb \u1ea3o tr\u00ean \u0111\u0129a, l\u00e0m gi\u1ea3m \u0111\u00e1ng k\u1ec3 hi\u1ec7u su\u1ea5t.<\/li>\n<\/ul>\n

                            Chi\u1ebfn l\u01b0\u1ee3c t\u1ed1i \u01b0u h\u00f3a hi\u1ec7u su\u1ea5t ERD \ud83d\ude80<\/h2>\n

                            \u0110\u1ec3 duy tr\u00ec s\u1ef1 c\u00e2n b\u1eb1ng l\u00e0nh m\u1ea1nh gi\u1eefa t\u00ednh to\u00e0n v\u1eb9n v\u00e0 t\u1ed1c \u0111\u1ed9, c\u00e1c chi\u1ebfn l\u01b0\u1ee3c c\u1ee5 th\u1ec3 c\u1ea7n \u0111\u01b0\u1ee3c \u00e1p d\u1ee5ng trong giai \u0111o\u1ea1n thi\u1ebft k\u1ebf.<\/p>\n

                            1. Ch\u1ec9 m\u1ee5c ch\u1ecdn l\u1ecdc<\/h3>\n

                            Kh\u00f4ng ch\u1ec9 m\u1ee5c t\u1ea5t c\u1ea3 c\u00e1c kh\u00f3a ngo\u1ea1i m\u1ed9t c\u00e1ch m\u00e1y m\u00f3c. Ph\u00e2n t\u00edch m\u1eabu truy v\u1ea5n.<\/p>\n

                              \n
                            • C\u00e1c ph\u00e9p n\u1ed1i t\u1ea7n su\u1ea5t cao:<\/strong> N\u1ebfu hai b\u1ea3ng th\u01b0\u1eddng xuy\u00ean \u0111\u01b0\u1ee3c n\u1ed1i, h\u00e3y ch\u1ec9 m\u1ee5c kh\u00f3a ngo\u1ea1i.<\/li>\n
                            • C\u00e1c m\u1ed1i quan h\u1ec7 hi\u1ebfm khi truy v\u1ea5n:<\/strong> N\u1ebfu m\u1ed9t m\u1ed1i quan h\u1ec7 hi\u1ebfm khi \u0111\u01b0\u1ee3c truy v\u1ea5n, chi ph\u00ed ch\u1ec9 m\u1ee5c c\u00f3 th\u1ec3 v\u01b0\u1ee3t qu\u00e1 l\u1ee3i \u00edch mang l\u1ea1i.<\/li>\n<\/ul>\n

                              2. Chia t\u00e1ch<\/h3>\n

                              Chia t\u00e1ch c\u00e1c b\u1ea3ng l\u1edbn c\u00f3 th\u1ec3 c\u00f4 l\u1eadp ki\u1ec3m tra kh\u00f3a ngo\u1ea1i v\u00e0o c\u00e1c \u0111o\u1ea1n d\u1eef li\u1ec7u c\u1ee5 th\u1ec3.<\/p>\n

                                \n
                              • Chia t\u00e1ch theo kho\u1ea3ng gi\u00e1 tr\u1ecb:<\/strong>Chia d\u1eef li\u1ec7u theo kho\u1ea3ng ng\u00e0y ho\u1eb7c ID.<\/li>\n
                              • T\u00e1c \u0111\u1ed9ng:<\/strong>Gi\u1ea3m k\u00edch th\u01b0\u1edbc c\u1ee7a ch\u1ec9 m\u1ee5c c\u1ea7n \u0111\u01b0\u1ee3c qu\u00e9t trong qu\u00e1 tr\u00ecnh ki\u1ec3m tra t\u00ednh to\u00e0n v\u1eb9n.<\/li>\n<\/ul>\n

                                3. X\u00e1c th\u1ef1c b\u1ea5t \u0111\u1ed3ng b\u1ed9<\/h3>\n

                                Trong m\u1ed9t s\u1ed1 h\u1ec7 th\u1ed1ng c\u00f3 l\u01b0u l\u01b0\u1ee3ng cao, t\u00ednh to\u00e0n v\u1eb9n tham chi\u1ebfu nghi\u00eam ng\u1eb7t \u0111\u01b0\u1ee3c th\u1ef1c thi m\u1ed9t c\u00e1ch b\u1ea5t \u0111\u1ed3ng b\u1ed9.<\/p>\n

                                  \n
                                • Quy tr\u00ecnh:<\/strong>D\u1eef li\u1ec7u \u0111\u01b0\u1ee3c ch\u00e8n m\u00e0 kh\u00f4ng c\u1ea7n ki\u1ec3m tra kh\u00f3a ngo\u1ea1i ngay l\u1eadp t\u1ee9c.<\/li>\n
                                • D\u1ecdn d\u1eb9p:<\/strong>M\u1ed9t t\u00e1c v\u1ee5 n\u1ec1n s\u1ebd x\u00e1c th\u1ef1c v\u00e0 d\u1ecdn d\u1eb9p c\u00e1c b\u1ea3n ghi b\u1ecb b\u1ecf r\u01a1i \u0111\u1ecbnh k\u1ef3.<\/li>\n
                                • L\u1ee3i \u00edch:<\/strong>C\u1ea3i thi\u1ec7n \u0111\u00e1ng k\u1ec3 hi\u1ec7u su\u1ea5t ghi, nh\u01b0ng v\u1edbi chi ph\u00ed l\u00e0 s\u1ef1 b\u1ea5t nh\u1ea5t d\u1eef li\u1ec7u t\u1ea1m th\u1eddi.<\/li>\n<\/ul>\n

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

                                  Ngay c\u1ea3 nh\u1eefng ki\u1ebfn tr\u00fac s\u01b0 c\u00f3 kinh nghi\u1ec7m c\u0169ng c\u00f3 th\u1ec3 m\u1eafc b\u1eaby khi thi\u1ebft k\u1ebf s\u01a1 \u0111\u1ed3 ERD v\u1edbi vi\u1ec7c s\u1eed d\u1ee5ng kh\u00f3a ngo\u1ea1i n\u1eb7ng n\u1ec1.<\/p>\n

                                    \n
                                  • M\u1ed1i quan h\u1ec7 n\u1ed1i ti\u1ebfp:<\/strong>Nh\u1eefng chu\u1ed7i d\u00e0i c\u00e1c kh\u00f3a ngo\u1ea1i (A \u2192 B \u2192 C \u2192 D) khi\u1ebfn c\u00e1c truy v\u1ea5n tr\u1edf n\u00ean s\u00e2u v\u00e0 kh\u00f3 t\u1ed1i \u01b0u h\u00f3a.<\/li>\n
                                  • Kh\u00f3a tham chi\u1ebfu t\u1ef1 th\u00e2n:<\/strong>M\u1ed9t b\u1ea3ng tham chi\u1ebfu ch\u00ednh n\u00f3 (v\u00ed d\u1ee5: Nh\u00e2n vi\u00ean \u2192 Qu\u1ea3n l\u00fd) c\u00f3 th\u1ec3 l\u00e0m ph\u1ee9c t\u1ea1p c\u00e1c truy v\u1ea5n \u0111\u1ec7 quy v\u00e0 chi\u1ebfn l\u01b0\u1ee3c l\u1eadp ch\u1ec9 m\u1ee5c.<\/li>\n
                                  • Kh\u00f3a ch\u00ednh r\u1ed9ng:<\/strong>Vi\u1ec7c s\u1eed d\u1ee5ng kh\u00f3a ch\u00ednh nhi\u1ec1u c\u1ed9t bu\u1ed9c kh\u00f3a ngo\u1ea1i ph\u1ea3i r\u1ed9ng, l\u00e0m ph\u00ecnh to t\u1ea5t c\u1ea3 c\u00e1c ch\u1ec9 m\u1ee5c con.<\/li>\n
                                  • B\u1ecf qua th\u1ed1ng k\u00ea:<\/strong>N\u1ebfu b\u1ed9 \u0111\u1ed9ng c\u01a1 c\u01a1 s\u1edf d\u1eef li\u1ec7u thi\u1ebfu c\u00e1c th\u1ed1ng k\u00ea c\u1eadp nh\u1eadt v\u1ec1 c\u00e1c c\u1ed9t kh\u00f3a ngo\u1ea1i, tr\u00ecnh l\u1eadp k\u1ebf ho\u1ea1ch truy v\u1ea5n c\u00f3 th\u1ec3 ch\u1ecdn c\u00e1c k\u1ebf ho\u1ea1ch th\u1ef1c thi k\u00e9m.<\/li>\n<\/ul>\n

                                    B\u1ea3o v\u1ec7 l\u01b0\u1ee3c \u0111\u1ed3 c\u1ee7a b\u1ea1n cho t\u01b0\u01a1ng lai \ud83d\udd2e<\/h2>\n

                                    Thi\u1ebft k\u1ebf \u0111\u1ec3 \u0111\u1ea1t hi\u1ec7u su\u1ea5t hi\u1ec7n t\u1ea1i l\u00e0 \u0111i\u1ec1u c\u1ea7n thi\u1ebft, nh\u01b0ng kh\u1ea3 n\u0103ng m\u1edf r\u1ed9ng \u0111\u00f2i h\u1ecfi t\u1ea7m nh\u00ecn xa. Kh\u00f3a ngo\u1ea1i c\u00f3 th\u1ec3 tr\u1edf th\u00e0nh \u0111i\u1ec3m ngh\u1ebdn khi kh\u1ed1i l\u01b0\u1ee3ng d\u1eef li\u1ec7u t\u0103ng theo c\u1ea5p s\u1ed1 nh\u00e2n.<\/p>\n

                                    1. M\u1edf r\u1ed9ng ngang<\/h3>\n

                                    Khi chuy\u1ec3n sang c\u01a1 s\u1edf d\u1eef li\u1ec7u ph\u00e2n t\u00e1n, c\u00e1c r\u00e0ng bu\u1ed9c kh\u00f3a ngo\u1ea1i tr\u1edf n\u00ean th\u00e1ch th\u1ee9c.<\/p>\n

                                      \n
                                    • Chia s\u1ebb d\u1eef li\u1ec7u:<\/strong>Kh\u00f3a ngo\u1ea1i v\u01b0\u1ee3t qua c\u00e1c shard r\u1ea5t kh\u00f3 duy tr\u00ec m\u00e0 kh\u00f4ng c\u00f3 s\u1ef1 ph\u1ed1i h\u1ee3p trung t\u00e2m.<\/li>\n
                                    • T\u00ednh nh\u1ea5t qu\u00e1n:<\/strong>Duy tr\u00ec c\u00e1c t\u00ednh ch\u1ea5t ACID tr\u00ean c\u00e1c n\u00fat c\u00f3 ph\u1ee5 thu\u1ed9c kh\u00f3a ngo\u1ea1i \u0111\u00f2i h\u1ecfi c\u00e1c giao th\u1ee9c ph\u1ee9c t\u1ea1p.<\/li>\n<\/ul>\n

                                      2. Ti\u1ebfn h\u00f3a l\u01b0\u1ee3c \u0111\u1ed3<\/h3>\n

                                      Khi y\u00eau c\u1ea7u thay \u0111\u1ed5i, c\u00e1c m\u1ed1i quan h\u1ec7 c\u00f3 th\u1ec3 c\u1ea7n \u0111\u01b0\u1ee3c \u0111i\u1ec1u ch\u1ec9nh.<\/p>\n

                                        \n
                                      • Thay \u0111\u1ed5i kh\u00f3a:<\/strong>Thay \u0111\u1ed5i r\u00e0ng bu\u1ed9c kh\u00f3a ngo\u1ea1i tr\u00ean m\u1ed9t b\u1ea3ng l\u1edbn c\u00f3 th\u1ec3 l\u00e0m kh\u00f3a b\u1ea3ng trong th\u1eddi gian d\u00e0i.<\/li>\n
                                      • Di chuy\u1ec3n:<\/strong>C\u00e1c c\u00f4ng c\u1ee5 d\u00f9ng cho di chuy\u1ec3n l\u01b0\u1ee3c \u0111\u1ed3 ph\u1ea3i x\u1eed l\u00fd \u0111\u01b0\u1ee3c c\u00e1c ph\u1ee5 thu\u1ed9c kh\u00f3a ngo\u1ea1i \u0111\u1ec3 tr\u00e1nh l\u00e0m h\u1ecfng d\u1eef li\u1ec7u s\u1ea3n xu\u1ea5t.<\/li>\n<\/ul>\n

                                        T\u00f3m t\u1eaft c\u00e1c y\u1ebfu t\u1ed1 c\u1ea7n xem x\u00e9t \ud83d\udcdd<\/h2>\n

                                        Vi\u1ec7c quy\u1ebft \u0111\u1ecbnh c\u00f3 \u0111\u01b0a kh\u00f3a ngo\u1ea1i v\u00e0o s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 (ERD) kh\u00f4ng ph\u1ea3i l\u00e0 m\u1ed9t l\u1ef1a ch\u1ecdn nh\u1ecb ph\u00e2n. \u0110\u00f3 l\u00e0 m\u1ed9t ph\u00e9p t\u00ednh gi\u1eefa nhu c\u1ea7u to\u00e0n v\u1eb9n d\u1eef li\u1ec7u v\u00e0 chi ph\u00ed hi\u1ec7u su\u1ea5t.<\/p>\n

                                          \n
                                        • To\u00e0n v\u1eb9n:<\/strong>Kh\u00f3a ngo\u1ea1i l\u00e0 c\u01a1 ch\u1ebf ch\u00ednh \u0111\u1ec3 t\u1ef1 \u0111\u1ed9ng th\u1ef1c thi c\u00e1c quy t\u1eafc d\u1eef li\u1ec7u.<\/li>\n
                                        • Hi\u1ec7u su\u1ea5t:<\/strong>Ch\u00fang t\u1ea1o ra chi ph\u00ed b\u1ed5 sung khi ghi d\u1eef li\u1ec7u v\u00e0 y\u00eau c\u1ea7u duy tr\u00ec ch\u1ec9 m\u1ee5c.<\/li>\n
                                        • Thi\u1ebft k\u1ebf:<\/strong>M\u1ed9t s\u01a1 \u0111\u1ed3 ERD s\u1ea1ch s\u1ebd h\u1ed7 tr\u1ee3 giao ti\u1ebfp, nh\u01b0ng m\u1ed9t s\u01a1 \u0111\u1ed3 ERD d\u00e0y \u0111\u1eb7c c\u00f3 th\u1ec3 cho th\u1ea5y t\u00ecnh tr\u1ea1ng qu\u00e1 chu\u1ea9n h\u00f3a.<\/li>\n
                                        • T\u1ed1i \u01b0u h\u00f3a:<\/strong>Ch\u1ec9 m\u1ee5c, ph\u00e2n v\u00f9ng v\u00e0 phi chu\u1ea9n h\u00f3a l\u00e0 c\u00e1c c\u00f4ng c\u1ee5 \u0111\u1ec3 qu\u1ea3n l\u00fd t\u00e1c \u0111\u1ed9ng c\u1ee7a kh\u00f3a ngo\u1ea1i.<\/li>\n<\/ul>\n

                                          B\u1eb1ng c\u00e1ch ph\u00e2n t\u00edch kh\u1ed1i l\u01b0\u1ee3ng c\u00f4ng vi\u1ec7c c\u1ee5 th\u1ec3 c\u1ee7a \u1ee9ng d\u1ee5ng, c\u00e1c ki\u1ebfn tr\u00fac s\u01b0 c\u00f3 th\u1ec3 x\u00e1c \u0111\u1ecbnh m\u1eadt \u0111\u1ed9 kh\u00f3a ngo\u1ea1i t\u1ed1i \u01b0u. M\u1ee5c ti\u00eau l\u00e0 m\u1ed9t l\u01b0\u1ee3c \u0111\u1ed3 \u0111\u1ee7 m\u1ea1nh \u0111\u1ec3 ng\u0103n ng\u1eeba l\u1ed7i nh\u01b0ng \u0111\u1ee7 linh ho\u1ea1t \u0111\u1ec3 x\u1eed l\u00fd vi\u1ec7c x\u1eed l\u00fd d\u1eef li\u1ec7u t\u1ed1c \u0111\u1ed9 cao.<\/p>\n

                                          Thi\u1ebft k\u1ebf c\u01a1 s\u1edf d\u1eef li\u1ec7u hi\u1ec7u qu\u1ea3 \u0111\u00f2i h\u1ecfi gi\u00e1m s\u00e1t li\u00ean t\u1ee5c. Khi c\u00e1c m\u1eabu d\u1eef li\u1ec7u thay \u0111\u1ed5i, hi\u1ec7u su\u1ea5t c\u1ee7a c\u00e1c kh\u00f3a ngo\u1ea1i c\u0169ng s\u1ebd thay \u0111\u1ed5i. Vi\u1ec7c xem x\u00e9t \u0111\u1ecbnh k\u1ef3 c\u00e1c k\u1ebf ho\u1ea1ch th\u1ef1c thi v\u00e0 th\u1ed1ng k\u00ea kh\u00f3a \u0111\u1ea3m b\u1ea3o r\u1eb1ng s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 v\u1eabn ph\u1ea3n \u00e1nh ch\u00ednh x\u00e1c h\u00e0nh vi c\u1ee7a h\u1ec7 th\u1ed1ng theo th\u1eddi gian.<\/p>\n","protected":false},"excerpt":{"rendered":"

                                          Khi c\u00e1c ki\u1ebfn tr\u00fac s\u01b0 thi\u1ebft k\u1ebf m\u00f4 h\u00ecnh d\u1eef li\u1ec7u, s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3 (ERD) \u0111\u00f3ng vai tr\u00f2 l\u00e0 b\u1ea3n v\u1ebd n\u1ec1n t\u1ea3ng. N\u00f3 kh\u00f4ng ch\u1ec9 \u0111\u01a1n…<\/p>\n","protected":false},"author":1,"featured_media":1650,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_title":"Kh\u00f3a ngo\u1ea1i v\u00e0 Hi\u1ec7u su\u1ea5t ERD: H\u01b0\u1edbng d\u1eabn k\u1ef9 thu\u1eadt \ud83d\udd11","_yoast_wpseo_metadesc":"Ph\u00e2n t\u00edch c\u00e1ch kh\u00f3a ngo\u1ea1i \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn hi\u1ec7u su\u1ea5t s\u01a1 \u0111\u1ed3 quan h\u1ec7 th\u1ef1c th\u1ec3. 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