{"id":476177,"date":"2023-08-09T07:26:52","date_gmt":"2023-08-09T07:26:52","guid":{"rendered":""},"modified":"2023-09-05T11:12:10","modified_gmt":"2023-09-05T11:12:10","slug":"cardinality","status":"publish","type":"wiki","link":"https:\/\/oneproxy.pro\/vn\/wiki\/cardinality\/","title":{"rendered":"H\u1ed3ng y"},"content":{"rendered":"<p>S\u1ed1 l\u01b0\u1ee3ng, trong b\u1ed1i c\u1ea3nh c\u01a1 s\u1edf d\u1eef li\u1ec7u v\u00e0 qu\u1ea3n l\u00fd d\u1eef li\u1ec7u, \u0111\u1ec1 c\u1eadp \u0111\u1ebfn c\u00e1c gi\u00e1 tr\u1ecb duy nh\u1ea5t c\u00f3 trong t\u1eadp d\u1eef li\u1ec7u ho\u1eb7c m\u1ed9t c\u1ed9t c\u1ee5 th\u1ec3 c\u1ee7a b\u1ea3ng c\u01a1 s\u1edf d\u1eef li\u1ec7u. N\u00f3 \u0111\u00f3ng m\u1ed9t vai tr\u00f2 quan tr\u1ecdng trong vi\u1ec7c t\u1ed1i \u01b0u h\u00f3a c\u01a1 s\u1edf d\u1eef li\u1ec7u, hi\u1ec7u su\u1ea5t truy v\u1ea5n v\u00e0 ph\u00e2n t\u00edch d\u1eef li\u1ec7u. Hi\u1ec3u \u0111\u01b0\u1ee3c s\u1ed1 l\u01b0\u1ee3ng c\u1ee7a t\u1eadp d\u1eef li\u1ec7u l\u00e0 \u0111i\u1ec1u c\u1ea7n thi\u1ebft \u0111\u1ec3 \u0111\u1ea3m b\u1ea3o vi\u1ec7c truy xu\u1ea5t v\u00e0 x\u1eed l\u00fd d\u1eef li\u1ec7u hi\u1ec7u qu\u1ea3.<\/p>\n<h2>L\u1ecbch s\u1eed v\u1ec1 ngu\u1ed3n g\u1ed1c c\u1ee7a Cardinality v\u00e0 l\u1ea7n \u0111\u1ea7u ti\u00ean \u0111\u1ec1 c\u1eadp \u0111\u1ebfn n\u00f3<\/h2>\n<p>Kh\u00e1i ni\u1ec7m l\u1ef1c l\u01b0\u1ee3ng c\u00f3 ngu\u1ed3n g\u1ed1c t\u1eeb l\u00fd thuy\u1ebft t\u1eadp h\u1ee3p v\u00e0 to\u00e1n h\u1ecdc. Thu\u1eadt ng\u1eef \u201ccardinality\u201d \u0111\u01b0\u1ee3c nh\u00e0 to\u00e1n h\u1ecdc ng\u01b0\u1eddi \u0110\u1ee9c Georg Cantor \u0111\u01b0a ra v\u00e0o nh\u1eefng n\u0103m 1870. Cantor l\u00e0 m\u1ed9t trong nh\u1eefng ng\u01b0\u1eddi ti\u00ean phong trong l\u0129nh v\u1ef1c l\u00fd thuy\u1ebft t\u1eadp h\u1ee3p, v\u00e0 \u00f4ng \u0111\u00e3 s\u1eed d\u1ee5ng l\u1ef1c l\u01b0\u1ee3ng \u0111\u1ec3 so s\u00e1nh k\u00edch th\u01b0\u1edbc c\u1ee7a c\u00e1c t\u1eadp h\u1ee3p kh\u00e1c nhau, th\u1eadm ch\u00ed c\u1ea3 nh\u1eefng t\u1eadp h\u1ee3p v\u00f4 h\u1ea1n. Theo th\u1eddi gian, kh\u00e1i ni\u1ec7m l\u1ef1c l\u01b0\u1ee3ng \u0111\u00e3 \u0111\u01b0\u1ee3c \u1ee9ng d\u1ee5ng trong nhi\u1ec1u l\u0129nh v\u1ef1c kh\u00e1c nhau, bao g\u1ed3m khoa h\u1ecdc m\u00e1y t\u00ednh v\u00e0 qu\u1ea3n l\u00fd c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/p>\n<h2>Th\u00f4ng tin chi ti\u1ebft v\u1ec1 Cardinality. M\u1edf r\u1ed9ng ch\u1ee7 \u0111\u1ec1 H\u1ed3ng y<\/h2>\n<p>Trong mi\u1ec1n c\u01a1 s\u1edf d\u1eef li\u1ec7u, s\u1ed1 l\u01b0\u1ee3ng th\u1ebb \u0111\u1ec1 c\u1eadp \u0111\u1ebfn s\u1ed1 l\u01b0\u1ee3ng gi\u00e1 tr\u1ecb duy nh\u1ea5t c\u00f3 trong m\u1ed9t c\u1ed9t c\u1ee7a b\u1ea3ng. N\u00f3 gi\u00fap qu\u1ea3n tr\u1ecb vi\u00ean v\u00e0 nh\u00e0 ph\u00e2n t\u00edch c\u01a1 s\u1edf d\u1eef li\u1ec7u hi\u1ec3u \u0111\u01b0\u1ee3c vi\u1ec7c ph\u00e2n ph\u1ed1i d\u1eef li\u1ec7u, x\u00e1c \u0111\u1ecbnh kh\u00f3a ch\u00ednh v\u00e0 t\u1ed1i \u01b0u h\u00f3a hi\u1ec7u su\u1ea5t truy v\u1ea5n. Cardinality th\u01b0\u1eddng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng c\u00f9ng v\u1edbi c\u00e1c ch\u1ec9 m\u1ee5c c\u01a1 s\u1edf d\u1eef li\u1ec7u \u0111\u1ec3 t\u0103ng t\u1ed1c \u0111\u1ed9 truy xu\u1ea5t d\u1eef li\u1ec7u.<\/p>\n<p>S\u1ed1 l\u01b0\u1ee3ng c\u1ee7a m\u1ed9t c\u1ed9t \u0111\u01b0\u1ee3c ph\u00e2n th\u00e0nh ba lo\u1ea1i:<\/p>\n<ol>\n<li>S\u1ed1 l\u01b0\u1ee3ng th\u1ea5p: M\u1ed9t c\u1ed9t c\u00f3 s\u1ed1 l\u01b0\u1ee3ng th\u1ea5p c\u00f3 m\u1ed9t s\u1ed1 l\u01b0\u1ee3ng nh\u1ecf c\u00e1c gi\u00e1 tr\u1ecb ri\u00eang bi\u1ec7t so v\u1edbi t\u1ed5ng s\u1ed1 h\u00e0ng trong b\u1ea3ng. C\u00e1c v\u00ed d\u1ee5 ph\u1ed5 bi\u1ebfn v\u1ec1 c\u00e1c c\u1ed9t s\u1ed1 l\u01b0\u1ee3ng th\u1ea5p l\u00e0 gi\u1edbi t\u00ednh, tr\u1ea1ng th\u00e1i ho\u1eb7c danh m\u1ee5c. C\u00e1c c\u1ed9t n\u00e0y th\u01b0\u1eddng ch\u1ee9a c\u00e1c gi\u00e1 tr\u1ecb l\u1eb7p l\u1ea1i, c\u00f3 th\u1ec3 kh\u00f4ng ph\u1ea3i l\u00e0 \u1ee9ng c\u1eed vi\u00ean l\u00fd t\u01b0\u1edfng \u0111\u1ec3 l\u1eadp ch\u1ec9 m\u1ee5c v\u00ec ch\u00fang c\u00f3 th\u1ec3 kh\u00f4ng l\u00e0m gi\u1ea3m \u0111\u00e1ng k\u1ec3 th\u1eddi gian truy v\u1ea5n.<\/li>\n<li>S\u1ed1 l\u01b0\u1ee3ng v\u1eeba ph\u1ea3i: M\u1ed9t c\u1ed9t c\u00f3 s\u1ed1 l\u01b0\u1ee3ng v\u1eeba ph\u1ea3i c\u00f3 s\u1ed1 l\u01b0\u1ee3ng gi\u00e1 tr\u1ecb ri\u00eang bi\u1ec7t v\u1eeba ph\u1ea3i. C\u00e1c c\u1ed9t n\u00e0y t\u1ea1o ra s\u1ef1 c\u00e2n b\u1eb1ng gi\u1eefa c\u00e1c c\u1ed9t c\u00f3 l\u01b0\u1ee3ng s\u1ed1 th\u1ea5p v\u00e0 cao v\u00e0 c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c xem x\u00e9t \u0111\u1ec3 l\u1eadp ch\u1ec9 m\u1ee5c trong m\u1ed9t s\u1ed1 tr\u01b0\u1eddng h\u1ee3p nh\u1ea5t \u0111\u1ecbnh.<\/li>\n<li>S\u1ed1 l\u01b0\u1ee3ng cao: M\u1ed9t c\u1ed9t c\u00f3 s\u1ed1 l\u01b0\u1ee3ng cao c\u00f3 s\u1ed1 l\u01b0\u1ee3ng l\u1edbn c\u00e1c gi\u00e1 tr\u1ecb duy nh\u1ea5t li\u00ean quan \u0111\u1ebfn s\u1ed1 l\u01b0\u1ee3ng h\u00e0ng trong b\u1ea3ng. V\u00ed d\u1ee5 bao g\u1ed3m kh\u00f3a ch\u00ednh, \u0111\u1ecba ch\u1ec9 email ho\u1eb7c t\u00ean ng\u01b0\u1eddi d\u00f9ng. C\u00e1c c\u1ed9t c\u00f3 l\u01b0\u1ee3ng s\u1ed1 cao l\u00e0 \u1ee9ng c\u1eed vi\u00ean xu\u1ea5t s\u1eafc cho vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c v\u00ec ch\u00fang d\u1eabn \u0111\u1ebfn vi\u1ec7c truy xu\u1ea5t d\u1eef li\u1ec7u hi\u1ec7u qu\u1ea3 h\u01a1n.<\/li>\n<\/ol>\n<h2>C\u1ea5u tr\u00fac b\u00ean trong c\u1ee7a Cardinality. Cardinality ho\u1ea1t \u0111\u1ed9ng nh\u01b0 th\u1ebf n\u00e0o<\/h2>\n<p>S\u1ed1 l\u01b0\u1ee3ng \u0111\u01b0\u1ee3c x\u00e1c \u0111\u1ecbnh b\u1eb1ng c\u00e1ch ph\u00e2n t\u00edch d\u1eef li\u1ec7u trong m\u1ed9t c\u1ed9t c\u1ee5 th\u1ec3 c\u1ee7a b\u1ea3ng. Qu\u00e1 tr\u00ecnh n\u00e0y bao g\u1ed3m vi\u1ec7c qu\u00e9t c\u1ed9t v\u00e0 \u0111\u1ebfm s\u1ed1 l\u01b0\u1ee3ng c\u00e1c gi\u00e1 tr\u1ecb ri\u00eang bi\u1ec7t hi\u1ec7n c\u00f3. S\u1ed1 l\u01b0\u1ee3ng gi\u00e1 tr\u1ecb duy nh\u1ea5t c\u00e0ng cao th\u00ec s\u1ed1 l\u01b0\u1ee3ng ph\u1ea7n t\u1eed c\u1ee7a c\u1ed9t c\u00e0ng cao.<\/p>\n<p>H\u1ec7 th\u1ed1ng qu\u1ea3n l\u00fd c\u01a1 s\u1edf d\u1eef li\u1ec7u (DBMS) duy tr\u00ec s\u1ed1 li\u1ec7u th\u1ed1ng k\u00ea v\u1ec1 l\u01b0\u1ee3ng s\u1ed1 \u0111\u1ec3 h\u1ed7 tr\u1ee3 t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n. Th\u00f4ng tin n\u00e0y \u0111\u01b0\u1ee3c tr\u00ecnh t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n s\u1eed d\u1ee5ng \u0111\u1ec3 quy\u1ebft \u0111\u1ecbnh k\u1ebf ho\u1ea1ch th\u1ef1c hi\u1ec7n hi\u1ec7u qu\u1ea3 nh\u1ea5t cho m\u1ed9t truy v\u1ea5n nh\u1ea5t \u0111\u1ecbnh, th\u01b0\u1eddng li\u00ean quan \u0111\u1ebfn c\u00e1c chi\u1ebfn l\u01b0\u1ee3c l\u1ef1a ch\u1ecdn ch\u1ec9 m\u1ee5c v\u00e0 tham gia.<\/p>\n<h2>Ph\u00e2n t\u00edch c\u00e1c t\u00ednh n\u0103ng ch\u00ednh c\u1ee7a Cardinality<\/h2>\n<p>C\u00e1c t\u00ednh n\u0103ng ch\u00ednh c\u1ee7a cardinality bao g\u1ed3m:<\/p>\n<ul>\n<li>T\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n: Cardinality \u0111\u00f3ng m\u1ed9t vai tr\u00f2 quan tr\u1ecdng trong vi\u1ec7c t\u1ed1i \u01b0u h\u00f3a hi\u1ec7u su\u1ea5t truy v\u1ea5n. B\u1eb1ng c\u00e1ch bi\u1ebft s\u1ed1 l\u01b0\u1ee3ng c\u1ed9t, tr\u00ecnh t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n c\u00f3 th\u1ec3 ch\u1ecdn ch\u1ec9 m\u1ee5c v\u00e0 chi\u1ebfn l\u01b0\u1ee3c k\u1ebft h\u1ee3p ph\u00f9 h\u1ee3p nh\u1ea5t \u0111\u1ec3 c\u1ea3i thi\u1ec7n th\u1eddi gian th\u1ef1c hi\u1ec7n truy v\u1ea5n.<\/li>\n<li>Ph\u00e2n ph\u1ed1i d\u1eef li\u1ec7u: Cardinality cung c\u1ea5p c\u00e1i nh\u00ecn s\u00e2u s\u1eafc v\u1ec1 vi\u1ec7c ph\u00e2n ph\u1ed1i d\u1eef li\u1ec7u. Hi\u1ec3u s\u1ef1 ph\u00e2n b\u1ed1 c\u1ee7a c\u00e1c gi\u00e1 tr\u1ecb trong m\u1ed9t c\u1ed9t l\u00e0 r\u1ea5t quan tr\u1ecdng \u0111\u1ec3 ph\u00e2n t\u00edch d\u1eef li\u1ec7u v\u00e0 ra quy\u1ebft \u0111\u1ecbnh.<\/li>\n<li>L\u1eadp ch\u1ec9 m\u1ee5c: Cardinality gi\u00fap x\u00e1c \u0111\u1ecbnh c\u1ed9t n\u00e0o ph\u00f9 h\u1ee3p \u0111\u1ec3 l\u1eadp ch\u1ec9 m\u1ee5c. C\u00e1c c\u1ed9t c\u00f3 s\u1ed1 l\u01b0\u1ee3ng cao th\u01b0\u1eddng l\u00e0 \u1ee9ng c\u1eed vi\u00ean t\u1ed1t h\u01a1n cho vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c v\u00ec ch\u00fang d\u1eabn \u0111\u1ebfn vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c c\u00f3 ch\u1ecdn l\u1ecdc h\u01a1n.<\/li>\n<\/ul>\n<h2>C\u00e1c lo\u1ea1i H\u1ed3ng Y<\/h2>\n<p>C\u00f3 ba lo\u1ea1i l\u01b0\u1ee3ng s\u1ed1 ch\u00ednh d\u1ef1a tr\u00ean s\u1ed1 l\u01b0\u1ee3ng gi\u00e1 tr\u1ecb ri\u00eang bi\u1ec7t trong m\u1ed9t c\u1ed9t, nh\u01b0 \u0111\u00e3 \u0111\u1ec1 c\u1eadp tr\u01b0\u1edbc \u0111\u00f3. \u0110\u00e2y l\u00e0 m\u1ed9t c\u00e1i nh\u00ecn t\u00f3m t\u1eaft:<\/p>\n<table>\n<thead>\n<tr>\n<th>Lo\u1ea1i s\u1ed1 l\u01b0\u1ee3ng<\/th>\n<th>S\u1ef1 mi\u00eau t\u1ea3<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>S\u1ed1 l\u01b0\u1ee3ng th\u1ea5p<\/td>\n<td>S\u1ed1 l\u01b0\u1ee3ng nh\u1ecf c\u00e1c gi\u00e1 tr\u1ecb ri\u00eang bi\u1ec7t so v\u1edbi t\u1ed5ng s\u1ed1 h\u00e0ng. Kh\u00f4ng l\u00fd t\u01b0\u1edfng cho vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c.<\/td>\n<\/tr>\n<tr>\n<td>S\u1ed1 l\u01b0\u1ee3ng v\u1eeba ph\u1ea3i<\/td>\n<td>S\u1ed1 l\u01b0\u1ee3ng v\u1eeba ph\u1ea3i c\u00e1c gi\u00e1 tr\u1ecb kh\u00e1c bi\u1ec7t. \u0110\u01b0\u1ee3c xem x\u00e9t \u0111\u1ec3 l\u1eadp ch\u1ec9 m\u1ee5c trong c\u00e1c t\u00ecnh hu\u1ed1ng c\u1ee5 th\u1ec3.<\/td>\n<\/tr>\n<tr>\n<td>Nhi\u1ec7t \u0111\u1ed9 cao<\/td>\n<td>S\u1ed1 l\u01b0\u1ee3ng l\u1edbn c\u00e1c gi\u00e1 tr\u1ecb duy nh\u1ea5t li\u00ean quan \u0111\u1ebfn s\u1ed1 l\u01b0\u1ee3ng h\u00e0ng. \u1ee8ng c\u1eed vi\u00ean xu\u1ea5t s\u1eafc cho vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>C\u00e1ch s\u1eed d\u1ee5ng Cardinality, c\u00e1c v\u1ea5n \u0111\u1ec1 v\u00e0 gi\u1ea3i ph\u00e1p li\u00ean quan \u0111\u1ebfn vi\u1ec7c s\u1eed d\u1ee5ng<\/h2>\n<h3>C\u00e1c c\u00e1ch s\u1eed d\u1ee5ng Cardinality:<\/h3>\n<ol>\n<li>T\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n: Th\u00f4ng tin v\u1ec1 s\u1ed1 l\u01b0\u1ee3ng r\u1ea5t quan tr\u1ecdng \u0111\u1ec3 t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n c\u01a1 s\u1edf d\u1eef li\u1ec7u. Vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c th\u00edch h\u1ee3p cho c\u00e1c c\u1ed9t c\u00f3 l\u01b0\u1ee3ng s\u1ed1 cao c\u00f3 th\u1ec3 c\u1ea3i thi\u1ec7n \u0111\u00e1ng k\u1ec3 hi\u1ec7u su\u1ea5t truy v\u1ea5n.<\/li>\n<li>Ph\u00e2n t\u00edch d\u1eef li\u1ec7u: Hi\u1ec3u c\u00e1ch ph\u00e2n ph\u1ed1i d\u1eef li\u1ec7u b\u1eb1ng c\u00e1ch s\u1eed d\u1ee5ng s\u1ed1 l\u01b0\u1ee3ng th\u1ebb gi\u00fap ph\u00e2n t\u00edch d\u1eef li\u1ec7u c\u00f3 \u00fd ngh\u0129a v\u00e0 ra quy\u1ebft \u0111\u1ecbnh.<\/li>\n<\/ol>\n<h3>V\u1ea5n \u0111\u1ec1 v\u00e0 gi\u1ea3i ph\u00e1p:<\/h3>\n<ol>\n<li>Th\u1ed1ng k\u00ea l\u1ed7i th\u1eddi: Th\u1ed1ng k\u00ea s\u1ed1 l\u01b0\u1ee3ng th\u1ebb l\u1ed7i th\u1eddi ho\u1eb7c kh\u00f4ng ch\u00ednh x\u00e1c c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn c\u00e1c k\u1ebf ho\u1ea1ch truy v\u1ea5n d\u01b0\u1edbi m\u1ee9c t\u1ed1i \u01b0u. Th\u01b0\u1eddng xuy\u00ean c\u1eadp nh\u1eadt s\u1ed1 li\u1ec7u th\u1ed1ng k\u00ea l\u00e0 \u0111i\u1ec1u c\u1ea7n thi\u1ebft \u0111\u1ec3 duy tr\u00ec hi\u1ec7u su\u1ea5t c\u01a1 s\u1edf d\u1eef li\u1ec7u.<\/li>\n<li>Ph\u00e2n ph\u1ed1i d\u1eef li\u1ec7u sai l\u1ec7ch: Ph\u00e2n ph\u1ed1i d\u1eef li\u1ec7u sai l\u1ec7ch c\u00f3 th\u1ec3 g\u00e2y ra c\u00e1c ch\u1ec9 m\u1ee5c m\u1ea5t c\u00e2n b\u1eb1ng, d\u1eabn \u0111\u1ebfn hi\u1ec7u su\u1ea5t truy v\u1ea5n k\u00e9m. Vi\u1ec7c ph\u00e2n v\u00f9ng ho\u1eb7c s\u1eed d\u1ee5ng s\u1ed1 li\u1ec7u th\u1ed1ng k\u00ea d\u1ef1a tr\u00ean bi\u1ec3u \u0111\u1ed3 c\u00f3 th\u1ec3 gi\u00fap gi\u1ea3m thi\u1ec3u v\u1ea5n \u0111\u1ec1 n\u00e0y.<\/li>\n<\/ol>\n<h2>C\u00e1c \u0111\u1eb7c \u0111i\u1ec3m ch\u00ednh v\u00e0 so s\u00e1nh kh\u00e1c v\u1edbi c\u00e1c thu\u1eadt ng\u1eef t\u01b0\u01a1ng t\u1ef1<\/h2>\n<table>\n<thead>\n<tr>\n<th>\u0111\u1eb7c tr\u01b0ng<\/th>\n<th>H\u1ed3ng y<\/th>\n<th>T\u1ec9 tr\u1ecdng<\/th>\n<th>T\u00ednh ch\u1ecdn l\u1ecdc<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>S\u1ef1 \u0111\u1ecbnh ngh\u0129a<\/td>\n<td>Gi\u00e1 tr\u1ecb duy nh\u1ea5t trong m\u1ed9t c\u1ed9t<\/td>\n<td>T\u1ef7 l\u1ec7 c\u00e1c gi\u00e1 tr\u1ecb ri\u00eang bi\u1ec7t tr\u00ean t\u1ed5ng s\u1ed1 h\u00e0ng trong m\u1ed9t c\u1ed9t<\/td>\n<td>\u0110o l\u01b0\u1eddng t\u00ednh duy nh\u1ea5t c\u1ee7a m\u1ed9t c\u1ed9t<\/td>\n<\/tr>\n<tr>\n<td>T\u00e1c \u0111\u1ed9ng \u0111\u1ebfn vi\u1ec7c l\u1eadp ch\u1ec9 m\u1ee5c<\/td>\n<td>S\u1ed1 l\u01b0\u1ee3ng cao d\u1eabn \u0111\u1ebfn c\u00e1c ch\u1ec9 s\u1ed1 ch\u1ecdn l\u1ecdc h\u01a1n<\/td>\n<td>M\u1eadt \u0111\u1ed9 cao c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn vi\u1ec7c l\u01b0u tr\u1eef nh\u1ecf g\u1ecdn h\u01a1n<\/td>\n<td>\u0110\u1ed9 ch\u1ecdn l\u1ecdc cao c\u00f3 ngh\u0129a l\u00e0 c\u1ed9t l\u1ecdc \u0111\u1ed9c \u0111\u00e1o h\u01a1n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>Quan \u0111i\u1ec3m v\u00e0 c\u00f4ng ngh\u1ec7 c\u1ee7a t\u01b0\u01a1ng lai li\u00ean quan \u0111\u1ebfn Cardinality<\/h2>\n<p>Khi d\u1eef li\u1ec7u ti\u1ebfp t\u1ee5c t\u0103ng v\u1ec1 s\u1ed1 l\u01b0\u1ee3ng v\u00e0 \u0111\u1ed9 ph\u1ee9c t\u1ea1p, s\u1ed1 l\u01b0\u1ee3ng d\u1eef li\u1ec7u s\u1ebd v\u1eabn l\u00e0 m\u1ed9t kh\u00e1i ni\u1ec7m c\u01a1 b\u1ea3n trong qu\u1ea3n l\u00fd v\u00e0 t\u1ed1i \u01b0u h\u00f3a c\u01a1 s\u1edf d\u1eef li\u1ec7u. C\u00e1c c\u00f4ng ngh\u1ec7 trong t\u01b0\u01a1ng lai c\u00f3 th\u1ec3 t\u1eadp trung v\u00e0o c\u00e1c ph\u01b0\u01a1ng ph\u00e1p th\u1ed1ng k\u00ea ti\u00ean ti\u1ebfn h\u01a1n \u0111\u1ec3 \u01b0\u1edbc t\u00ednh ch\u00ednh x\u00e1c l\u01b0\u1ee3ng s\u1ed1, \u0111\u1eb7c bi\u1ec7t l\u00e0 trong m\u00f4i tr\u01b0\u1eddng d\u1eef li\u1ec7u l\u1edbn v\u00e0 ph\u00e2n t\u00e1n.<\/p>\n<p>V\u1edbi nh\u1eefng ti\u1ebfn b\u1ed9 kh\u00f4ng ng\u1eebng trong tr\u00ed tu\u1ec7 nh\u00e2n t\u1ea1o v\u00e0 h\u1ecdc m\u00e1y, \u01b0\u1edbc t\u00ednh l\u01b0\u1ee3ng s\u1ed1 c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c h\u01b0\u1edfng l\u1ee3i t\u1eeb c\u00e1c m\u00f4 h\u00ecnh d\u1ef1 \u0111o\u00e1n \u0111\u1ec3 t\u1ef1 \u0111\u1ed9ng t\u1ed1i \u01b0u h\u00f3a hi\u1ec7u su\u1ea5t truy v\u1ea5n. H\u01a1n n\u1eefa, c\u00e1c ph\u01b0\u01a1ng ph\u00e1p m\u1edbi \u0111\u1ec3 x\u1eed l\u00fd s\u1ed1 l\u01b0\u1ee3ng d\u1eef li\u1ec7u b\u00e1n c\u1ea5u tr\u00fac v\u00e0 phi c\u1ea5u tr\u00fac c\u00f3 th\u1ec3 xu\u1ea5t hi\u1ec7n \u0111\u1ec3 h\u1ed7 tr\u1ee3 c\u00e1c \u0111\u1ecbnh d\u1ea1ng d\u1eef li\u1ec7u hi\u1ec7n \u0111\u1ea1i v\u00e0 c\u00e1c ngu\u1ed3n d\u1eef li\u1ec7u \u0111a d\u1ea1ng.<\/p>\n<h2>C\u00e1ch s\u1eed d\u1ee5ng ho\u1eb7c li\u00ean k\u1ebft m\u00e1y ch\u1ee7 proxy v\u1edbi Cardinality<\/h2>\n<p>M\u00e1y ch\u1ee7 proxy \u0111\u00f3ng m\u1ed9t vai tr\u00f2 quan tr\u1ecdng trong vi\u1ec7c truy xu\u1ea5t v\u00e0 b\u1ea3o m\u1eadt d\u1eef li\u1ec7u cho c\u00e1c \u1ee9ng d\u1ee5ng kh\u00e1c nhau, bao g\u1ed3m qu\u00e9t web, thu th\u1eadp d\u1eef li\u1ec7u v\u00e0 l\u1ecdc n\u1ed9i dung. Khi s\u1eed d\u1ee5ng m\u00e1y ch\u1ee7 proxy, vi\u1ec7c hi\u1ec3u \u0111\u01b0\u1ee3c s\u1ed1 l\u01b0\u1ee3ng d\u1eef li\u1ec7u \u0111\u01b0\u1ee3c truy xu\u1ea5t c\u00f3 th\u1ec3 mang l\u1ea1i l\u1ee3i \u00edch theo m\u1ed9t s\u1ed1 c\u00e1ch:<\/p>\n<ol>\n<li>\u0110\u1ecbnh tuy\u1ebfn truy v\u1ea5n: M\u00e1y ch\u1ee7 proxy c\u00f3 th\u1ec3 \u0111\u1ecbnh tuy\u1ebfn truy v\u1ea5n \u0111\u1ebfn c\u00e1c m\u00e1y ch\u1ee7 c\u1ee5 th\u1ec3 d\u1ef1a tr\u00ean s\u1ed1 l\u01b0\u1ee3ng d\u1eef li\u1ec7u \u0111\u1ec3 c\u00e2n b\u1eb1ng t\u1ea3i v\u00e0 n\u00e2ng cao hi\u1ec7u su\u1ea5t.<\/li>\n<li>Qu\u1ea3n l\u00fd b\u1ed9 \u0111\u1ec7m: Th\u00f4ng tin v\u1ec1 s\u1ed1 l\u01b0\u1ee3ng c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 x\u00e1c \u0111\u1ecbnh d\u1eef li\u1ec7u n\u00e0o s\u1ebd \u0111\u01b0\u1ee3c l\u01b0u v\u00e0o b\u1ed9 \u0111\u1ec7m tr\u00ean m\u00e1y ch\u1ee7 proxy, t\u1ed1i \u01b0u h\u00f3a c\u00e1c y\u00eau c\u1ea7u trong t\u01b0\u01a1ng lai.<\/li>\n<\/ol>\n<h2>Li\u00ean k\u1ebft li\u00ean quan<\/h2>\n<p>\u0110\u1ec3 bi\u1ebft th\u00eam th\u00f4ng tin v\u1ec1 Cardinality v\u00e0 vai tr\u00f2 c\u1ee7a n\u00f3 trong qu\u1ea3n l\u00fd v\u00e0 t\u1ed1i \u01b0u h\u00f3a c\u01a1 s\u1edf d\u1eef li\u1ec7u, h\u00e3y tham kh\u1ea3o c\u00e1c t\u00e0i nguy\u00ean sau:<\/p>\n<ol>\n<li><a href=\"https:\/\/en.wikipedia.org\/wiki\/Cardinality_(data_modeling)\" target=\"_new\" rel=\"noopener nofollow\">Wikipedia \u2013 Cardinality (m\u00f4 h\u00ecnh h\u00f3a d\u1eef li\u1ec7u)<\/a><\/li>\n<li><a href=\"https:\/\/docs.microsoft.com\/en-us\/sql\/relational-databases\/statistics\/cardinality-estimation-database-engine?view=sql-server-ver15\" target=\"_new\" rel=\"noopener nofollow\">Microsoft Docs \u2013 \u01af\u1edbc t\u00ednh s\u1ed1 l\u01b0\u1ee3ng<\/a><\/li>\n<li><a href=\"https:\/\/docs.oracle.com\/database\/121\/TGSQL\/tgsql_statisticsconcepts.htm#TGSQL888\" target=\"_new\" rel=\"noopener nofollow\">Oracle \u2013 T\u00ednh t\u1ed5ng qu\u00e1t v\u00e0 t\u00ednh ch\u1ecdn l\u1ecdc<\/a><\/li>\n<\/ol>\n<p>T\u00f3m l\u1ea1i, Cardinality \u0111\u00f3ng vai tr\u00f2 c\u01a1 b\u1ea3n trong qu\u1ea3n l\u00fd c\u01a1 s\u1edf d\u1eef li\u1ec7u, t\u1ed1i \u01b0u h\u00f3a truy v\u1ea5n v\u00e0 ph\u00e2n t\u00edch d\u1eef li\u1ec7u. Hi\u1ec3u \u0111\u01b0\u1ee3c s\u1ed1 l\u01b0\u1ee3ng d\u1eef li\u1ec7u l\u00e0 \u0111i\u1ec1u c\u1ea7n thi\u1ebft \u0111\u1ec3 truy xu\u1ea5t, l\u01b0u tr\u1eef d\u1eef li\u1ec7u v\u00e0 hi\u1ec7u su\u1ea5t c\u01a1 s\u1edf d\u1eef li\u1ec7u t\u1ed5ng th\u1ec3 hi\u1ec7u qu\u1ea3. Khi d\u1eef li\u1ec7u ti\u1ebfp t\u1ee5c ph\u00e1t tri\u1ec3n, nh\u1eefng ti\u1ebfn b\u1ed9 trong c\u00f4ng ngh\u1ec7 v\u00e0 ph\u01b0\u01a1ng ph\u00e1p th\u1ed1ng k\u00ea c\u00f3 th\u1ec3 s\u1ebd g\u00f3p ph\u1ea7n v\u00e0o c\u00e1c k\u1ef9 thu\u1eadt t\u1ed1i \u01b0u h\u00f3a v\u00e0 \u01b0\u1edbc t\u00ednh l\u01b0\u1ee3ng s\u1ed1 ch\u00ednh x\u00e1c h\u01a1n. B\u1eb1ng c\u00e1ch t\u1eadn d\u1ee5ng kh\u00e1i ni\u1ec7m Cardinality c\u00f9ng v\u1edbi m\u00e1y ch\u1ee7 proxy, c\u00e1c doanh nghi\u1ec7p v\u00e0 t\u1ed5 ch\u1ee9c c\u00f3 th\u1ec3 n\u00e2ng cao c\u00e1c bi\u1ec7n ph\u00e1p qu\u1ea3n l\u00fd, ph\u00e2n t\u00edch v\u00e0 b\u1ea3o m\u1eadt d\u1eef li\u1ec7u c\u1ee7a m\u00ecnh.<\/p>","protected":false},"featured_media":0,"menu_order":0,"template":"","meta":{"_acf_changed":false,"content-type":"","inline_featured_image":false,"footnotes":""},"class_list":["post-476177","wiki","type-wiki","status-publish","hentry"],"acf":{"faq_title":"Frequently Asked Questions about <mark>Cardinality: A Comprehensive Guide<\/mark>","faq_items":[{"question":"What is Cardinality, and how does it relate to databases?","answer":"<p>Cardinality refers to the number of unique values present in a column of a database table. It is a crucial concept in database management as it helps optimize query performance, analyze data distribution, and identify suitable candidates for indexing. Understanding Cardinality enables efficient data retrieval and improves overall database performance.<\/p>"},{"question":"Who introduced the concept of Cardinality, and where did it originate?","answer":"<p>The concept of Cardinality was introduced by the German mathematician Georg Cantor in the 1870s. He used it in set theory to compare the sizes of different sets, even infinite ones. Over time, Cardinality found its application in various fields, including computer science and database management.<\/p>"},{"question":"What are the different types of Cardinality, and how are they categorized?","answer":"<p>Cardinality is categorized into three types based on the number of unique values in a column:<\/p><ol><li>Low Cardinality: A column with a small number of distinct values compared to the total number of rows.<\/li><li>Moderate Cardinality: A column with a moderate number of distinct values, striking a balance between low and high Cardinality.<\/li><li>High Cardinality: A column with a large number of unique values relative to the number of rows.<\/li><\/ol>"},{"question":"How does Cardinality impact query optimization and data analysis?","answer":"<p>Cardinality plays a vital role in query optimization. By understanding the distribution of data and the uniqueness of values, the query optimizer can choose the most suitable index and join strategies, leading to faster query execution times. Additionally, Cardinality provides insights into data distribution, which is essential for meaningful data analysis and decision-making.<\/p>"},{"question":"What are some common problems related to Cardinality, and how can they be addressed?","answer":"<p>Outdated or inaccurate Cardinality statistics can lead to suboptimal query plans. Regularly updating statistics is essential to maintain database performance. Skewed data distributions can also cause imbalanced indexes, resulting in poor query performance. Partitioning or using histogram-based statistics can help mitigate this issue.<\/p>"},{"question":"How does Cardinality differ from other similar terms like density and selectivity?","answer":"<p>Cardinality refers to the unique values in a column, while density is the ratio of distinct values to total rows in a column, and selectivity measures the uniqueness of a column for filtering. Each term serves different purposes in database management, and understanding their distinctions is crucial for efficient data handling.<\/p>"},{"question":"What are the future perspectives and technologies related to Cardinality?","answer":"<p>As data continues to grow in volume and complexity, Cardinality will remain essential in database management and optimization. Future technologies may focus on more advanced statistical methods for accurate Cardinality estimation, especially in distributed and big data environments. Predictive models and new approaches for handling semi-structured and unstructured data may also emerge.<\/p>"},{"question":"How can proxy servers be associated with Cardinality in data retrieval and security?","answer":"<p>Proxy servers can use Cardinality information to optimize query routing, balancing the load and enhancing performance. Additionally, Cardinality can help determine which data should be cached on proxy servers, improving future requests and contributing to enhanced data retrieval and security practices.<\/p>"}]},"_links":{"self":[{"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/wiki\/476177","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/wiki"}],"about":[{"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/types\/wiki"}],"version-history":[{"count":0,"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/wiki\/476177\/revisions"}],"wp:attachment":[{"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/media?parent=476177"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}