{"id":6294,"date":"2024-11-14T11:17:47","date_gmt":"2024-11-14T03:17:47","guid":{"rendered":"https:\/\/fwq.ai\/blog\/6294\/"},"modified":"2024-11-14T11:17:47","modified_gmt":"2024-11-14T03:17:47","slug":"%e4%ba%86%e8%a7%a3-mysql-%e6%9f%a5%e8%af%a2%e4%bc%98%e5%8c%96%e5%99%a8%ef%bc%9acountid-%e4%b8%8e-count","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/6294\/","title":{"rendered":"\u4e86\u89e3 MySQL \u67e5\u8be2\u4f18\u5316\u5668\uff1aCOUNT(id) \u4e0e COUNT(*)"},"content":{"rendered":"

\"\u4e86\u89e3<\/p>\n

\u5728 MySQL \u4e2d\uff0c\u6211\u4eec\u51e0\u4e4e\u6bcf\u5929\u90fd\u4f1a\u4f7f\u7528\u201cCOUNT\u201d\u51fd\u6570\u6765\u5e2e\u52a9\u6211\u4eec\u8ba1\u7b97\u7ed9\u5b9a\u67e5\u8be2\u7684\u884c\u6570\u3002\u6bcf\u4e2a\u5f00\u53d1\u8005\u5173\u4e8e\u6027\u80fd\u7684\u6700\u5927\u56f0\u5883\u662f\u4f7f\u7528\u201cCOUNT(*)\u201d\u8fd8\u662f\u201cCOUNT(id)\u201d\u66f4\u597d\u3002<\/p>\n

\n

MySQL\u4f18\u5316\u5668 <\/h2>\n

MySQL \u4f18\u5316\u5668\u662f MySQL \u7684\u5173\u952e\u7ec4\u4ef6\uff0c\u8d1f\u8d23\u786e\u5b9a\u6267\u884c\u7ed9\u5b9a SQL \u67e5\u8be2\u7684\u6700\u6709\u6548\u65b9\u5f0f\u3002\u8fd9\u90e8\u5206\u5728\u201cCOUNT\u201d\u6700\u5feb\u7684\u56f0\u5883\u4e2d\u8d77\u7740\u5173\u952e\u4f5c\u7528\u3002\u90a3\u4e48\u8ba9\u6211\u4eec\u89e3\u91ca\u4e00\u4e0b…<\/p>\n

\u6211\u4eec\u521b\u5efa\u201cusers\u201d\u8868\uff0c\u8be5\u8868\u5c06\u5728\u201cfirst_name\u201d\u5217\u4e0a\u6709\u4e00\u4e2a\u7d22\u5f15\uff1a<\/p>\n

\u521b\u5efa\u8868\u7528\u6237\uff08\n    id int NOT NULL AUTO_INCRMENT,\n    \u540d\u5b57 varchar(256) NOT NULL,\n    \u4e3b\u952e\uff08id\uff09\uff0c\n    \u7d22\u5f15 idx_first_name (first_name)\n\uff09\uff1b\n<\/pre>\n
  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
\u6211\u4eec\u6dfb\u52a0\u51e0\u884c\u5e76\u8fd0\u884c\u4ee5\u4e0b 2 \u4e2a\u67e5\u8be2\uff1a<\/p>\n
\u89e3\u91ca SELECT COUNT(id) FROM \u7528\u6237\uff1b\n<\/pre>\n
  \u767b\u5f55\u540e\u590d\u5236    <\/p>\n
\u89e3\u91ca SELECT COUNT(*) FROM \u7528\u6237\uff1b\n<\/pre>\n
  \u767b\u5f55\u540e\u590d\u5236   <\/p>\n
\u5f53\u4f60\u8fd0\u884c\u8fd9\u4e24\u4e2a SQL \u67e5\u8be2\u65f6\uff0c\u4f60\u4f1a\u6ce8\u610f\u5230\u5b83\u4eec\u4f7f\u7528\u76f8\u540c\u7684\u7d22\u5f15\uff0c\u201cCOUNT(*)\u201d\u4e00\u70b9\u4e5f\u4e0d\u6162\uff0cMySQL \u4f18\u5316\u5668\u8d1f\u8d23\u8fd9\u4e00\u70b9\uff0c\u5b83\u4f1a\u5728\u8868\u4e2d\u627e\u5230\u7d22\u5f15\uff0c\u4ece\u800c\u7ed9\u51fa\u6700\u68d2\u7684\u8868\u6f14\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u4e24\u4e2a\u67e5\u8be2\u5c06\u4ee5\u76f8\u540c\u7684\u901f\u5ea6\u8fd4\u56de\u6570\u636e\uff0c\u56e0\u4e3a\u5b83\u4eec\u4f7f\u7528\u76f8\u540c\u7684\u7d22\u5f15\uff0c\u5e76\u4e14 MySQL \u4f18\u5316\u5668\u8ba4\u4e3a\u8be5\u7d22\u5f15\u662f\u6700\u6709\u6548\u7684\u3002<\/p>\n
MySQL \u4f18\u5316\u5668\u8003\u8651\u4e86\u8bb8\u591a\u6709\u52a9\u4e8e\u9009\u62e9\u6700\u4f73\u7d22\u5f15\u952e\u7684\u53c2\u6570\uff0c\u4ee5\u4fbf\u7ed9\u5b9a\u7684\u67e5\u8be2\u5c3d\u5feb\u8fd4\u56de\u6570\u636e\u3002<\/p>\n
\n
 \u7ed3\u8bba <\/h2>\n
\u901a\u5e38\u5efa\u8bae\u4f7f\u7528\u201cCOUNT(*)\u201d\uff0c\u56e0\u4e3a\u5b83\u5141\u8bb8 MySQL \u4f18\u5316\u5668\u9009\u62e9\u6700\u6709\u6548\u7684\u65b9\u6cd5\uff0c\u800c\u201cCOUNT(column_name)\u201d\u5728\u9700\u8981\u4ec5\u8ba1\u7b97\u975e NULL \u503c\u7684\u60c5\u51b5\u4e0b\u7279\u522b\u6709\u7528\u200b\u200b\u5728\u7279\u5b9a\u7684\u4e13\u680f\u4e2d\u3002\u4e86\u89e3 MySQL \u4f18\u5316\u5668\u7684\u5de5\u4f5c\u539f\u7406\u4ee5\u53ca\u5982\u4f55\u4f7f\u7528\u7d22\u5f15\u5bf9\u4e8e\u5b9e\u73b0\u6700\u4f73\u67e5\u8be2\u6027\u80fd\u81f3\u5173\u91cd\u8981\u3002<\/p>\n
\u4ee5\u4e0a\u5c31\u662f\u4e86\u89e3 MySQL \u67e5\u8be2\u4f18\u5316\u5668\uff1aCOUNT(id) \u4e0e COUNT(*)\u7684\u8be6\u7ec6\u5185\u5bb9\uff0c\u66f4\u591a\u8bf7\u5173\u6ce8\u7c73\u4e91\u7f51\u5176\u5b83\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"
\u5728 MySQL \u4e2d\uff0c\u6211\u4eec\u51e0\u4e4e\u6bcf\u5929\u90fd\u4f1a\u4f7f\u7528\u201cCOUNT\u201d\u51fd\u6570\u6765\u5e2e\u52a9\u6211\u4eec\u8ba1\u7b97\u7ed9\u5b9a\u67e5\u8be2\u7684\u884c\u6570\u3002\u6bcf\u4e2a\u5f00\u53d1\u8005\u5173\u4e8e\u6027\u80fd\u7684\u6700\u5927\u56f0\u5883\u662f\u4f7f\u7528\u201cCOUNT(*)\u201d\u8fd8\u662f\u201cCOUNT(id)\u201d\u66f4\u597d\u3002 MySQL\u4f18\u5316\u5668 MySQL \u4f18\u5316\u5668\u662f MySQL \u7684\u5173\u952e\u7ec4\u4ef6\uff0c\u8d1f\u8d23\u786e\u5b9a\u6267\u884c\u7ed9\u5b9a SQL \u67e5\u8be2\u7684\u6700\u6709\u6548\u65b9\u5f0f\u3002\u8fd9\u90e8\u5206\u5728\u201cCOUNT\u201d\u6700\u5feb\u7684\u56f0\u5883\u4e2d\u8d77\u7740\u5173\u952e\u4f5c\u7528\u3002\u90a3\u4e48\u8ba9\u6211\u4eec\u89e3\u91ca\u4e00\u4e0b… \u6211\u4eec\u521b\u5efa\u201cusers\u201d\u8868\uff0c\u8be5\u8868\u5c06\u5728\u201cfirst_name\u201d\u5217\u4e0a\u6709\u4e00\u4e2a\u7d22\u5f15\uff1a \u521b\u5efa\u8868\u7528\u6237\uff08 id int NOT NULL AUTO_INCRMENT, \u540d\u5b57 varchar(256) NOT NULL, \u4e3b\u952e\uff08id\uff09\uff0c \u7d22\u5f15 idx_first_name (first_name) \uff09\uff1b \u767b\u5f55\u540e\u590d\u5236 \u6211\u4eec\u6dfb\u52a0\u51e0\u884c\u5e76\u8fd0\u884c\u4ee5\u4e0b 2 \u4e2a\u67e5\u8be2\uff1a \u89e3\u91ca SELECT COUNT(id) FROM \u7528\u6237\uff1b \u767b\u5f55\u540e\u590d\u5236 \u89e3\u91ca SELECT COUNT(*) FROM \u7528\u6237\uff1b \u767b\u5f55\u540e\u590d\u5236 \u5f53\u4f60\u8fd0\u884c\u8fd9\u4e24\u4e2a SQL \u67e5\u8be2\u65f6\uff0c\u4f60\u4f1a\u6ce8\u610f\u5230\u5b83\u4eec\u4f7f\u7528\u76f8\u540c\u7684\u7d22\u5f15\uff0c\u201cCOUNT(*)\u201d\u4e00\u70b9\u4e5f\u4e0d\u6162\uff0cMySQL \u4f18\u5316\u5668\u8d1f\u8d23\u8fd9\u4e00\u70b9\uff0c\u5b83\u4f1a\u5728\u8868\u4e2d\u627e\u5230\u7d22\u5f15\uff0c\u4ece\u800c\u7ed9\u51fa\u6700\u68d2\u7684\u8868\u6f14\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u4e24\u4e2a\u67e5\u8be2\u5c06\u4ee5\u76f8\u540c\u7684\u901f\u5ea6\u8fd4\u56de\u6570\u636e\uff0c\u56e0\u4e3a\u5b83\u4eec\u4f7f\u7528\u76f8\u540c\u7684\u7d22\u5f15\uff0c\u5e76\u4e14 MySQL \u4f18\u5316\u5668\u8ba4\u4e3a\u8be5\u7d22\u5f15\u662f\u6700\u6709\u6548\u7684\u3002 MySQL \u4f18\u5316\u5668\u8003\u8651\u4e86\u8bb8\u591a\u6709\u52a9\u4e8e\u9009\u62e9\u6700\u4f73\u7d22\u5f15\u952e\u7684\u53c2\u6570\uff0c\u4ee5\u4fbf\u7ed9\u5b9a\u7684\u67e5\u8be2\u5c3d\u5feb\u8fd4\u56de\u6570\u636e\u3002 \u7ed3\u8bba \u901a\u5e38\u5efa\u8bae\u4f7f\u7528\u201cCOUNT(*)\u201d\uff0c\u56e0\u4e3a\u5b83\u5141\u8bb8 MySQL \u4f18\u5316\u5668\u9009\u62e9\u6700\u6709\u6548\u7684\u65b9\u6cd5\uff0c\u800c\u201cCOUNT(column_name)\u201d\u5728\u9700\u8981\u4ec5\u8ba1\u7b97\u975e NULL […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-6294","post","type-post","status-publish","format-standard","hentry","category-16"],"_links":{"self":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/6294","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/comments?post=6294"}],"version-history":[{"count":0,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/6294\/revisions"}],"wp:attachment":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/media?parent=6294"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/categories?post=6294"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/tags?post=6294"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}