{"id":16443,"date":"2024-10-22T10:31:55","date_gmt":"2024-10-22T02:31:55","guid":{"rendered":"https:\/\/92it.top\/?p=16443"},"modified":"2024-10-22T10:31:55","modified_gmt":"2024-10-22T02:31:55","slug":"mysql%e7%95%99%e7%96%91%e9%97%ae%ef%bc%9aleft-join%e6%97%b6%e9%80%89on%e8%bf%98%e6%98%afwhere%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/92it.top\/?p=16443","title":{"rendered":"MySQL\u7559\u7591\u95ee\uff1aleft join\u65f6\u9009on\u8fd8\u662fwhere\uff1f"},"content":{"rendered":"\n

\u8f6c\u8f7d\uff1aMySQL\u7559\u7591\u95ee\uff1aleft join\u65f6\u9009on\u8fd8\u662fwhere\uff1f<\/a><\/p>\n\n\n\n

\u524d\u5929\u5199SQL\u65f6\u672c\u60f3\u901a\u8fc7 A left B join on and <\/code>\u540e\u9762\u7684\u6761\u4ef6\u6765\u4f7f\u67e5\u51fa\u7684\u4e24\u6761\u8bb0\u5f55\u53d8\u6210\u4e00\u6761\uff0c\u5948\u4f55\u53d1\u73b0\u8fd8\u662f\u6709\u4e24\u6761\u3002<\/p>\n\n\n\n

\u540e\u6765\u53d1\u73b0 join on and<\/code> \u4e0d\u4f1a\u8fc7\u6ee4\u7ed3\u679c\u8bb0\u5f55\u6761\u6570\uff0c\u53ea\u4f1a\u6839\u636eand\u540e\u7684\u6761\u4ef6\u662f\u5426\u663e\u793a B\u8868\u7684\u8bb0\u5f55\uff0cA\u8868\u7684\u8bb0\u5f55\u4e00\u5b9a\u4f1a\u663e\u793a\u3002<\/p>\n\n\n\n

\u4e0d\u7ba1and \u540e\u9762\u7684\u662fA.id=1<\/code>\u8fd8\u662fB.id=1<\/code>\uff0c\u90fd\u663e\u793a\u51faA\u8868\u4e2d\u6240\u6709\u7684\u8bb0\u5f55\uff0c\u5e76\u5173\u8054\u663e\u793aB\u4e2d\u5bf9\u5e94A\u8868\u4e2did\u4e3a1\u7684\u8bb0\u5f55\u6216\u8005B\u8868\u4e2did\u4e3a1\u7684\u8bb0\u5f55\u3002<\/p>\n\n\n\n

\u8fd0\u884csql:<\/p>\n\n\n\n

SELECT *\nFROM student s\n LEFT JOIN class c ON s.classId = c.id\nORDER BY s.id<\/pre>\n\n\n
\n
\"\"<\/figure><\/div>\n\n\n
\u8fd0\u884csql:<\/p>\n\n\n\n
SELECT *\nFROM student s\n LEFT JOIN class c\n ON s.classId = c.id\n  AND s.name = '\u5f20\u4e09'\nORDER BY s.id<\/pre>\n\n\n
\n
\"\"<\/figure><\/div>\n\n\n
\u8fd0\u884csql:<\/p>\n\n\n\n
SELECT *\nFROM student s\n LEFT JOIN class c\n ON s.classId = c.id\n  AND c.name = '\u4e09\u5e74\u7ea7\u4e09\u73ed'\nORDER BY s.id<\/pre>\n\n\n
\n
\"\"<\/figure><\/div>\n\n\n
\u6570\u636e\u5e93\u5728\u901a\u8fc7\u8fde\u63a5\u4e24\u5f20\u6216\u591a\u5f20\u8868\u6765\u8fd4\u56de\u8bb0\u5f55\u65f6\uff0c\u90fd\u4f1a\u751f\u6210\u4e00\u5f20\u4e2d\u95f4\u7684\u4e34\u65f6\u8868\uff0c\u7136\u540e\u518d\u5c06\u8fd9\u5f20\u4e34\u65f6\u8868\u8fd4\u56de\u7ed9\u7528\u6237\u3002<\/p>\n\n\n\n
\u5728\u4f7f\u7528left join<\/code>\u65f6\uff0con<\/code>\u548cwhere<\/code>\u6761\u4ef6\u7684\u533a\u522b\u5982\u4e0b\uff1a<\/p>\n\n\n\n
    \n
  • on\u6761\u4ef6\u662f\u5728\u751f\u6210\u4e34\u65f6\u8868\u65f6\u4f7f\u7528\u7684\u6761\u4ef6\uff0c\u5b83\u4e0d\u7ba1on\u4e2d\u7684\u6761\u4ef6\u662f\u5426\u4e3a\u771f\uff0c\u90fd\u4f1a\u8fd4\u56de\u5de6\u8fb9\u8868\u4e2d\u7684\u8bb0\u5f55\u3002<\/li>\n\n\n\n
  • where\u6761\u4ef6\u662f\u5728\u4e34\u65f6\u8868\u751f\u6210\u597d\u540e\uff0c\u518d\u5bf9\u4e34\u65f6\u8868\u8fdb\u884c\u8fc7\u6ee4\u7684\u6761\u4ef6\u3002\u8fd9\u65f6\u5df2\u7ecf\u6ca1\u6709left join<\/code>\u7684\u542b\u4e49\uff08\u5fc5\u987b\u8fd4\u56de\u5de6\u8fb9\u8868\u7684\u8bb0\u5f55\uff09\u4e86\uff0c\u6761\u4ef6\u4e0d\u4e3a\u771f\u7684\u5c31\u5168\u90e8\u8fc7\u6ee4\u6389\u3002<\/li>\n<\/ul>\n\n\n\n
    \u5047\u8bbe\u6709\u4e24\u5f20\u8868\uff1a<\/strong><\/p>\n\n\n\n
    \u88681\uff1atab2<\/p>\n\n\n
    \n
    \"\"<\/figure><\/div>\n\n\n
    \u88682\uff1atab2<\/p>\n\n\n
    \n
    \"\"<\/figure><\/div>\n\n\n
    \u4e24\u6761SQL:<\/p>\n\n\n\n
    \u7b2c\u4e00\u6761\uff1a<\/p>\n\n\n\n
    select * form tab1 left join tab2 on (tab1.size = tab2.size) where tab2.name=\u2019AAA\u2019<\/pre>\n\n\n\n
    \u7b2c\u4e8c\u6761\uff1a<\/p>\n\n\n\n
    select * form tab1 left join tab2 on (tab1.size = tab2.size and tab2.name=\u2019AAA\u2019)<\/pre>\n\n\n\n
    \u7b2c\u4e00\u6761SQL\u7684\u8fc7\u7a0b\uff1a<\/strong><\/p>\n\n\n\n
    1\u3001\u4e2d\u95f4\u8868on\u6761\u4ef6:<\/p>\n\n\n\n
    tab1.size = tab2.size<\/code><\/p>\n\n\n
    \n
    \"\"<\/figure><\/div>\n\n\n
    2\u3001\u518d\u5bf9\u4e2d\u95f4\u8868\u8fc7\u6ee4 where \u6761\u4ef6\uff1a<\/p>\n\n\n\n
    tab2.name=\u2019AAA\u2019<\/code><\/p>\n\n\n
    \n
    \"\"<\/figure><\/div>\n\n\n
    \u7b2c\u4e8c\u6761SQL\u7684\u8fc7\u7a0b\uff1a<\/strong><\/p>\n\n\n\n
    1\u3001\u4e2d\u95f4\u8868on\u6761\u4ef6:<\/p>\n\n\n\n
    tab1.size = tab2.size and tab2.name=\u2019AAA\u2019<\/code><\/p>\n\n\n\n
    PS\uff1a\u6761\u4ef6\u4e0d\u4e3a\u771f\u4e5f\u4f1a\u8fd4\u56de\u5de6\u8868\u4e2d\u7684\u8bb0\u5f55<\/p>\n\n\n
    \n
    \"\"<\/figure><\/div>\n\n\n
    \u5176\u5b9e\u4ee5\u4e0a\u7ed3\u679c\u7684\u5173\u952e\u539f\u56e0\u5c31\u662fleft join<\/code>\uff0cright join<\/code>\uff0cfull join<\/code>\u7684\u7279\u6b8a\u6027\uff0c\u4e0d\u7ba1on\u4e0a\u7684\u6761\u4ef6\u662f\u5426\u4e3a\u771f\u90fd\u4f1a\u8fd4\u56deleft\u6216right\u8868\u4e2d\u7684\u8bb0\u5f55\uff0cfull\u5219\u5177\u6709left\u548cright\u7684\u7279\u6027\u7684\u5e76\u96c6\u3002<\/p>\n\n\n\n
    \u800cinner jion<\/code>\u6ca1\u8fd9\u4e2a\u7279\u6b8a\u6027\uff0c\u5219\u6761\u4ef6\u653e\u5728on\u4e2d\u548cwhere\u4e2d\uff0c\u8fd4\u56de\u7684\u7ed3\u679c\u96c6\u662f\u76f8\u540c\u7684\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
    \u8f6c\u8f7d\uff1aMySQL\u7559\u7591\u95ee\uff1aleft join\u65f6\u9009on\u8fd8\u662fwhere\uff1f \u524d\u5929\u5199SQL\u65f6\u672c\u60f3\u901a\u8fc7 A left B  […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[],"_links":{"self":[{"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts\/16443"}],"collection":[{"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=16443"}],"version-history":[{"count":1,"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts\/16443\/revisions"}],"predecessor-version":[{"id":16452,"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts\/16443\/revisions\/16452"}],"wp:attachment":[{"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=16443"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=16443"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=16443"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}