{"id":5348,"date":"2020-07-29T21:23:02","date_gmt":"2020-07-29T13:23:02","guid":{"rendered":"http:\/\/39.97.231.10\/?p=5348"},"modified":"2020-07-29T21:23:02","modified_gmt":"2020-07-29T13:23:02","slug":"mysql%e6%80%a7%e8%83%bd%e4%bc%98%e5%8c%96-group-by%e8%af%ad%e5%8f%a5%e4%bc%98%e5%8c%96","status":"publish","type":"post","link":"http:\/\/www.weijing.co\/?p=5348","title":{"rendered":"MySQL\u6027\u80fd\u4f18\u5316-group by\u8bed\u53e5\u4f18\u5316"},"content":{"rendered":"<div class=\\\"blog_content\\\">\n<div class=\\\"blog_detail\\\">\n<div>\nMySQL\u5728\u5904\u7406group by\u8bed\u53e5\u65f6\uff0c\u6700\u5e38\u89c4\u7684\u65b9\u5f0f\u662f\u626b\u63cf\u6574\u4e2a\u8868\uff0c\u7136\u540e\u521b\u5efa\u4e00\u4e2a\u4e34\u65f6\u8868\uff0c\u4f7f\u7528\u4e34\u65f6\u8868\u5b58\u50a8\u5206\u7ec4\u548c\u805a\u5408\u51fd\u6570\u7684\u503c\u3002\u4f46\u662f\u5728\u4e00\u4e9b\u7279\u522b\u7684\u573a\u666f\u4e0b\uff0c\u901a\u8fc7\u7d22\u5f15\u53ef\u4ee5\u907f\u514d\u521b\u5efa\u4e34\u65f6\u8868\uff0c\u4ee5\u83b7\u53d6\u66f4\u597d\u7684\u6027\u80fd\u3002<br \/>\ngroup by \u5b50\u53e5\u4f7f\u7528\u7d22\u5f15\u7684\u5148\u51b3\u6761\u4ef6\u662fgroup by\u7684\u5b57\u6bb5\u5fc5\u987b\u90fd\u5728\u540c\u4e00\u4e2a\u7d22\u5f15\u91cc\uff0c\u8fd9\u6837\u624d\u80fd\u4f7f\u7528\u7d22\u5f15\u5df2\u7ecf\u6392\u597d\u5e8f\u7684\u7279\u6027\u3002group by \u8d70\u7d22\u5f15\uff0c\u901a\u5e38\u6709\u4e24\u79cd\u7d22\u5f15\u626b\u63cf\u65b9\u5f0f\u3002<\/p>\n<ul>\n<li>\u677e\u6563\u7d22\u5f15\u626b\u63cf\uff0cLoose Index Scan<\/li>\n<li>\u7d27\u51d1\u7d22\u5f15\u626b\u63cf\uff0cTight Index Scan<\/li>\n<\/ul>\n<h4>\u4e00\u3001\u677e\u6563\u7d22\u5f15\u626b\u63cf<\/h4>\n<p>\u6700\u6709\u6548\u7684\u5904\u7406group by\u7684\u65b9\u5f0f\u5c31\u662f\u901a\u8fc7\u7d22\u5f15\u80fd\u591f\u76f4\u63a5\u83b7\u53d6\u5230\u6240\u6709\u5206\u7ec4\u5b57\u6bb5\uff0c\u8fd9\u79cd\u65b9\u5f0f\u80fd\u591f\u5229\u7528\u7d22\u5f15\u672c\u8eab\u6709\u5e8f\u7684\u7279\u6027\uff0c\u53e6\u5916\u901a\u8fc7where\u6761\u4ef6\uff0c\u53ef\u4ee5\u4e0d\u7528\u626b\u63cf\u7d22\u5f15\u4e2d\u7684\u6240\u6709key\uff0c\u53ea\u9700\u8981\u8bfb\u53d6\u4e0e\u5206\u7ec4\u6570\u91cf\u76f8\u540c\u7684key\u6570\u91cf\uff0c\u8fd9\u4e2a\u6570\u91cf\u663e\u7136\u5927\u591a\u6570\u573a\u666f\u4e0b\u4f1a\u6bd4\u7d22\u5f15\u4e2d\u6240\u6709key\u7684\u6570\u91cf\u8981\u5c0f\u5f88\u591a\u3002\u5c24\u5176\u5bf9\u4e8e\u8303\u56f4\u5206\u7ec4\u67e5\u8be2\uff0c\u677e\u6563\u7d22\u5f15\u626b\u63cf\u4ece\u6bcf\u4e2a\u5206\u7ec4\u7684\u7b2c\u4e00\u4e2akey\u5f00\u59cb\u67e5\u627e\uff0c\u800c\u4e0d\u662f\u4ece\u6240\u6709key\u7684\u6700\u5c0f\u503c\u90a3\u4e2a\u5f00\u59cb\u67e5\u627e\u3002<br \/>\n\u677e\u6563\u7d22\u5f15\u626b\u63cf\u9700\u8981\u6ee1\u8db3\u4e00\u5b9a\u7684\u6761\u4ef6\uff1a<\/p>\n<ol>\n<li>\u67e5\u8be2\u53ea\u80fd\u6d89\u53ca\u4e00\u5f20\u8868<\/li>\n<li>group by\u5b57\u6bb5\u53ea\u80fd\u662f\u4e00\u4e2a\u7d22\u5f15\u7684\u6700\u5de6\u524d\u7f00\uff0c\u4e14\u4e0d\u80fd\u6709\u5176\u4ed6\u7684\u5b57\u6bb5\u3002\u6bd4\u5982\u4e00\u4e2a\u8868\u6709\u4e00\u4e2a\u8054\u5408\u7d22\u5f15(c1,c2,c3)\uff0cgroup by c1,c2 \u53ef\u4ee5\u4f7f\u7528\u677e\u6563\u7d22\u5f15\u626b\u63cf\uff0c\u800cgroup by c2,c3 \u6216\u8005 group by c1,c2,c4 \u5219\u4e0d\u80fd\u4f7f\u7528\u677e\u6563\u7d22\u5f15\u626b\u63cf<\/li>\n<li>\u805a\u5408\u51fd\u6570\u53ea\u80fd\u4f7f\u7528min\u6216\u8005max\uff0c\u5982\u679c\u8fd9\u4e24\u4e2a\u51fd\u6570\u540c\u65f6\u4f7f\u7528\u7684\u8bdd\uff0c\u53ea\u80fd\u5728\u540c\u4e00\u4e2a\u5b57\u6bb5\u4e0a\u4f7f\u7528\uff0c\u8fd9\u4e2a\u5b57\u6bb5\u4e5f\u5fc5\u987b\u5728\u7d22\u5f15\u4e2d\u3002\u770b\u4e00\u4e2a\u793a\u4f8b\uff0c\u5982\u4e0b\uff1a<br \/>\nselect c1,c2,min(c3),max(c3) from t1 group by c1,c2;<br \/>\n\u8054\u5408\u7d22\u5f15\uff1a(c1,c2,c3)<\/li>\n<li>\u8054\u5408\u7d22\u5f15\u4e2d\u7684\u5b57\u6bb5\uff0c\u9664\u4e86group by \u4ee5\u5916\u7684\uff0c\u5fc5\u987b\u4e3a\u5e38\u91cf\u3002\u793a\u4f8b\u5982\u4e0b\uff1a<br \/>\nSELECT c1, c2 FROM t1 WHERE c3 = const GROUP BY c1, c2;<br \/>\n\u8054\u5408\u7d22\u5f15\uff1a(c1,c2,c3)<\/li>\n<li>\u8054\u5408\u7d22\u5f15\u4e2d\u7684\u5b57\u6bb5\u5fc5\u987b\u662f\u6574\u4e2a\u5b57\u6bb5\u503c\u88ab\u7d22\u5f15\uff0c\u800c\u4e0d\u80fd\u662f\u524d\u7f00\uff0c\u6bd4\u5982(c1(10),c2,c3)<\/li>\n<\/ol>\n<p>\u5982\u679cgroup by \u53ef\u4ee5\u8d70\u677e\u6563\u7d22\u5f15\u626b\u63cf\uff0c\u90a3\u4e48\u6267\u884c\u8ba1\u5212\u4e2d\u7684Extra\u5b57\u6bb5\u5c06\u4f1a\u663e\u793a\u4e3a\uff1aUsing index for group-by\u3002<\/p>\n<h4>\u4e8c\u3001\u7d27\u51d1\u7d22\u5f15\u626b\u63cf<\/h4>\n<p>\u7d27\u51d1\u7d22\u5f15\u626b\u63cf\u4f1a\u6839\u636e\u6761\u4ef6\uff0c\u5bf9\u7d22\u5f15\u8fdb\u884c\u4e00\u6b21\u5168\u7d22\u5f15\u626b\u63cf\u6216\u8005\u4e00\u4e2a\u8303\u56f4\u7684\u7d22\u5f15\u626b\u63cf\u3002\u76f8\u5bf9\u4e8e\u677e\u6563\u7d22\u5f15\u626b\u63cf\u53ea\u9700\u8981\u626b\u63cf\u90e8\u5206\u6ee1\u8db3\u6761\u4ef6\u7684key\uff0c\u7d27\u51d1\u7d22\u5f15\u626b\u63cf\u9700\u8981\u626b\u63cf\u5168\u90e8\u7d22\u5f15\u6216\u8005\u6574\u4e2a\u8303\u56f4\u7d22\u5f15\u91cc\u9762\u7684key\u3002<br \/>\n\u7d27\u51d1\u7d22\u5f15\u626b\u63cf\u793a\u4f8b\uff1a<br \/>\nSELECT c1, c2, c3 FROM t1 WHERE c2 = \\&#8217;a\\&#8217; GROUP BY c1, c3;<br \/>\nSELECT c1, c2, c3 FROM t1 WHERE c1 = \\&#8217;a\\&#8217; GROUP BY c2, c3;<br \/>\n\u8054\u5408\u7d22\u5f15\uff1aidx(c1,c2,c3)<\/p>\n<h4>\u4e09\u3001\u4f18\u5316\u5efa\u8bae\uff1a<\/h4>\n<p>group by \u5c3d\u91cf\u901a\u8fc7\u8d70\u7d22\u5f15\u800c\u51cf\u5c11\u4e34\u65f6\u8868\u3001\u6392\u5e8f\u3001\u5168\u8868\u626b\u63cf\u3002\u5c3d\u53ef\u80fd\u521b\u9020\u8d70\u677e\u6563\u7d22\u5f15\u626b\u63cf\u7684\u6761\u4ef6\uff0c\u5176\u6b21\u662f\u7d27\u51d1\u7d22\u5f15\u626b\u63cf\uff0c\u901a\u8fc7\u5df2\u6709\u7d22\u5f15\uff0c\u63d0\u9ad8group by \u6027\u80fd\u3002\n<\/p><\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>MySQL\u5728\u5904\u7406group by\u8bed\u53e5\u65f6\uff0c\u6700\u5e38\u89c4\u7684\u65b9\u5f0f\u662f\u626b\u63cf\u6574\u4e2a\u8868\uff0c\u7136\u540e\u521b\u5efa\u4e00\u4e2a\u4e34\u65f6\u8868\uff0c\u4f7f\u7528\u4e34\u65f6\u8868\u5b58\u50a8\u5206\u7ec4\u548c\u805a\u5408 &hellip;<\/p>\n<p class=\"read-more\"> <a class=\"\" href=\"http:\/\/www.weijing.co\/?p=5348\"> <span class=\"screen-reader-text\">MySQL\u6027\u80fd\u4f18\u5316-group by\u8bed\u53e5\u4f18\u5316<\/span> \u67e5\u770b\u5168\u6587 &raquo;<\/a><\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"default","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"default","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":""},"categories":[90,88],"tags":[],"uagb_featured_image_src":{"full":false,"thumbnail":false,"medium":false,"medium_large":false,"large":false,"1536x1536":false,"2048x2048":false,"mailpoet_newsletter_max":false,"woocommerce_thumbnail":false,"woocommerce_single":false,"woocommerce_gallery_thumbnail":false,"shop_catalog":false,"shop_single":false,"shop_thumbnail":false},"uagb_author_info":{"display_name":"weijing","author_link":"http:\/\/www.weijing.co\/?author=4"},"uagb_comment_info":1,"uagb_excerpt":"MySQL\u5728\u5904\u7406group by\u8bed\u53e5\u65f6\uff0c\u6700\u5e38\u89c4\u7684\u65b9\u5f0f\u662f\u626b\u63cf\u6574\u4e2a\u8868\uff0c\u7136\u540e\u521b\u5efa\u4e00\u4e2a\u4e34\u65f6\u8868\uff0c\u4f7f\u7528\u4e34\u65f6\u8868\u5b58\u50a8\u5206\u7ec4\u548c\u805a\u5408&hellip;","_links":{"self":[{"href":"http:\/\/www.weijing.co\/index.php?rest_route=\/wp\/v2\/posts\/5348"}],"collection":[{"href":"http:\/\/www.weijing.co\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.weijing.co\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.weijing.co\/index.php?rest_route=\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5348"}],"version-history":[{"count":0,"href":"http:\/\/www.weijing.co\/index.php?rest_route=\/wp\/v2\/posts\/5348\/revisions"}],"wp:attachment":[{"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5348"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5348"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5348"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}