{"id":1952,"date":"2020-07-29T21:28:26","date_gmt":"2020-07-29T13:28:26","guid":{"rendered":"http:\/\/39.97.231.10\/?p=1952"},"modified":"2020-07-29T21:28:26","modified_gmt":"2020-07-29T13:28:26","slug":"mysql%e6%b4%be%e7%94%9f%e8%a1%a8%e4%bc%98%e5%8c%96","status":"publish","type":"post","link":"http:\/\/www.weijing.co\/?p=1952","title":{"rendered":"MySQL\u6d3e\u751f\u8868\u4f18\u5316"},"content":{"rendered":"
\n
\n1. \u4ec0\u4e48\u662fMySQL\u6d3e\u751f\u8868\uff1f<\/span>\n<\/div>\n<\/div>\n
\n
\n\u6d3e\u751f\u8868\uff08Derived Table\uff09\uff0c\u662f\u590d\u6742SQL\u5728\u6267\u884c\u8fc7\u7a0b\u4e2d\u7684\u4e2d\u95f4\u8868\uff0c\u4e5f\u53ef\u8ba4\u4e3a\u662f\u4e34\u65f6\u8868\uff0c\u5b58\u653eSQL\u6267\u884c\u8fc7\u7a0b\u4e2d\u5fc5\u4e0d\u53ef\u5c11\u7684\u4e2d\u95f4\u6570\u636e\u3002\u901a\u5e38\u7531\u8ddf\u5728from\u5b50\u53e5\u6216\u8005join\u5b50\u53e5\u4e4b\u540e\u7684\u5b50\u67e5\u8be2\u4ea7\u751f\uff0c\u6bd4\u5982\u4e0b\u9762\u4e24\u4e2a\u6d3e\u751f\u8868\u4f8b\u5b50\uff0cderived_t1\u548cderived_t2\u90fd\u662f\u6d3e\u751f\u8868\u3002
\nselect * from (select * from t1) as derived_t1;
\nselect t1.* from t1 join (select distinct class_id from t2) as derived_t2 where t1.id=derived_t2.class_id;<\/p>\n

2. MySQL\u4f18\u5316\u5668\u5982\u4f55\u5904\u7406\u6d3e\u751f\u8868\uff1f<\/h4>\n

MySQL\u4f18\u5316\u5668\u5904\u7406\u6d3e\u751f\u8868\u6709\u4e24\u79cd\u7b56\u7565\uff1a<\/p>\n

    \n
  1. \u5c06\u6d3e\u751f\u751f\u5408\u5e76(Merging)\u5230\u5916\u90e8\u7684\u67e5\u8be2\u5757<\/li>\n
  2. \u7269\u5316(Materialize)\u6d3e\u751f\u8868\u5230\u5185\u90e8\u7684\u4e34\u65f6\u8868<\/li>\n<\/ol>\n
    2.1 \u5408\u5e76(Merging\u00a0)<\/h5>\n

    \u5bf9\u4e8e\u7b80\u5355\u7684\u6d3e\u751f\u8868\uff0c\u6bd4\u5982\u6ca1\u6709\u4f7f\u7528group by\uff0chaving\uff0cdistinct\uff0climit\u7b49\uff0c\u8fd9\u7c7b\u6d3e\u751f\u8868\u53ef\u76f4\u63a5\u5408\u5e76\u5230\u5916\u90e8\u7684\u67e5\u8be2\u5757\u4e2d\u3002\u5982\u4e0b\u9762\u4e24\u4e2a\u4f8b\u5b50\uff1a
    \n\u4f8b\u5b501\uff1a<\/strong>
    \nSELECT * FROM (SELECT * FROM t1) AS derived_t1;
    \n\u5408\u5e76\u540e\u53d8\u6210\uff1a
    \nSELECT * FROM t1;
    \n\u4f8b\u5b502\uff1a<\/strong>
    \nSELECT * FROM t1 JOIN (SELECT t2.f1 FROM t2) AS derived_t2 ON t1.f2=derived_t2.f1 WHERE t1.f1 > 0;
    \n\u5408\u5e76\u540e\u53d8\u6210\uff1a
    \nSELECT t1.* FROM t1 JOIN t2 ON t1.f2=t2.f1 WHERE t1.f1 > 0;<\/p>\n

    2.2 \u7269\u5316(Materialization)<\/h5>\n

    \u6240\u8c13\u7269\u5316\uff0c\u53ef\u4ee5\u7406\u89e3\u4e3a\u5728\u5185\u5b58\u4e2d\u751f\u6210\u4e00\u5f20\u4e34\u65f6\u8868\uff0c\u5c06\u6d3e\u751f\u8868\u5b9e\u4f8b\u5316\uff0c\u7269\u5316\u6d3e\u751f\u8868\u6210\u672c\u8f83\u9ad8\uff0c\u5c24\u5176\u5f53\u6d3e\u751f\u8868\u5f88\u5927\uff0c\u5185\u5b58\u4e0d\u591f\u7528\u65f6\uff0c\u7269\u5316\u7684\u6d3e\u751f\u8868\u8fd8\u8981\u8f6c\u5b58\u5230\u78c1\u76d8\u4e2d\uff0c\u5bf9\u6027\u80fd\u5f71\u54cd\u8fdb\u4e00\u6b65\u589e\u52a0\u3002<\/p>\n

    2.3 \u4f18\u5316\u5668\u5bf9\u6d3e\u751f\u8868\u505a\u7684\u4f18\u5316<\/h5>\n
      \n
    1. \u5bf9\u4e8e\u7b80\u5355\u7684\u6d3e\u751f\u8868\uff0c\u8fdb\u884c\u5408\u5e76\u5904\u7406\u3002\u6d3e\u751f\u8868\u5408\u5e76\u4e5f\u6709\u9650\u5236\uff0c\u5f53\u5916\u5c42\u67e5\u8be2\u5757\u6d89\u53ca\u7684\u8868\u6570\u91cf\u8d85\u8fc7\u4e00\u5b9a\u9608\u503c(61)\u65f6\uff0c\u4f18\u5316\u5668\u5c06\u9009\u62e9\u7269\u5316\u6d3e\u751f\u8868\uff0c\u800c\u4e0d\u662f\u5408\u5e76\u6d3e\u751f\u8868\u3002<\/li>\n
    2. MySQL\u4f18\u5316\u5668\u5728\u5904\u7406\u6d3e\u751f\u8868\u65f6\uff0c\u80fd\u5408\u5e76\u7684\u5148\u5408\u5e76\uff0c\u4e0d\u80fd\u5408\u5e76\u7684\uff0c\u8003\u8651\u7269\u5316\u6d3e\u751f\u8868\uff0c\u7136\u800c\u7269\u5316\u6d3e\u751f\u8868\u4e5f\u662f\u6709\u6210\u672c\u7684\uff0c\u4f18\u5316\u5668\u4e5f\u4f1a\u5c3d\u91cf\u63a8\u8fdf\u6d3e\u751f\u8868\u7684\u7269\u5316\uff0c\u751a\u81f3\u4e0d\u7269\u5316\u6d3e\u751f\u8868\u3002\u6bd4\u5982join\u7684\u4e24\u4e2a\u8868\uff0cA\u4e3a\u6d3e\u751f\u8868\uff0c\u53e6\u5916\u4e00\u4e2a\u8868\u4e3aB\uff0c\u4f18\u5316\u5668\u63a8\u8fdf\u6d3e\u751f\u8868A\u7684\u7269\u5316\uff0c\u5148\u5904\u7406\u8868B\uff0c\u5f53\u8868B\u4e2d\u7684\u6570\u636e\u6839\u636e\u6761\u4ef6\u8fc7\u6ee4\u540e\uff0c\u6570\u636e\u5f88\u5c11\uff0c\u6216\u8005\u5b8c\u5168\u6ca1\u6709\u6570\u636e\u65f6\uff0c\u6b64\u65f6\u7269\u5316\u6d3e\u751f\u8868A\u6210\u672c\u5c31\u4f1a\u4f4e\u5f88\u591a\uff0c\u751a\u81f3\u4e0d\u7528\u7269\u5316\u6d3e\u751f\u8868\u3002<\/li>\n
    3. \u67e5\u8be2\u6761\u4ef6\u4ece\u5916\u5c42\u67e5\u8be2\u4e0b\u63a8\u5230\u6d3e\u751f\u8868\u4e2d\uff0c\u4ee5\u4fbf\u751f\u6210\u66f4\u5c0f\u7684\u6d3e\u751f\u8868\uff0c\u8d8a\u5c0f\u7684\u6d3e\u751f\u8868\uff0c\u5176\u6027\u80fd\u8d8a\u597d\u3002<\/li>\n
    4. \u4f18\u5316\u5668\u5c06\u4f1a\u5bf9\u7269\u5316\u7684\u6d3e\u751f\u8868\u589e\u52a0\u7d22\u5f15\uff0c\u4ee5\u52a0\u901f\u8bbf\u95ee\u3002\u6bd4\u5982\u4e0b\u9762\u8fd9\u4e2a\u4f8b\u5b50\uff0c\u4f18\u5316\u5668\u5c06\u4f1a\u5bf9derived_t2\u7684f1\u5b57\u6bb5\u6dfb\u52a0\u7d22\u5f15\uff0c\u4ee5\u63d0\u9ad8\u67e5\u8be2\u6027\u80fd\u3002
      \nSELECT * FROM t1 JOIN (SELECT DISTINCT f1 FROM t2) AS derived_t2 ON t1.f1=derived_t2.f1;<\/li>\n<\/ol>\n

      3. \u6d3e\u751f\u8868\u5408\u5e76\u5f00\u5173<\/h4>\n

      \u6d3e\u751f\u8868\u5408\u5e76\uff0c\u901a\u8fc7\u53c2\u6570optimizer_switch\u6765\u63a7\u5236\u662f\u5426\u6253\u5f00\uff0c\u9ed8\u8ba4\u4e3a\u6253\u5f00\u3002
      \noptimizer_switch=\\’derived_merge=ON\\’;<\/p>\n

      4. \u6d3e\u751f\u8868\u5408\u5e76\u9650\u5236<\/h4>\n

      \u4e0d\u662f\u6240\u6709\u7684\u6d3e\u751f\u8868\u90fd\u53ef\u4ee5\u88abmerge\uff0c\u7b80\u5355\u7684\u6d3e\u751f\u8868\uff0c\u53ef\u4ee5\u88abmerge\uff0c\u590d\u6742\u7684\u5e26\u6709GROUP\uff0cHAVING\uff0cDISTINCT\uff0cLIMIT\uff0c\u805a\u96c6\u51fd\u6570\u7b49\u5b50\u53e5\u7684\u6d3e\u751f\u8868\u53ea\u80fd\u88ab\u7269\u5316\uff0c\u4e0d\u80fd\u88ab\u5408\u5e76\u3002\n<\/p><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

      1. \u4ec0\u4e48\u662fMySQL\u6d3e\u751f\u8868\uff1f \u6d3e\u751f\u8868\uff08Derived Table\uff09\uff0c\u662f\u590d\u6742SQL\u5728\u6267\u884c\u8fc7\u7a0b\u4e2d\u7684\u4e2d\u95f4\u8868\uff0c\u4e5f\u53ef\u8ba4 …<\/p>\n

      MySQL\u6d3e\u751f\u8868\u4f18\u5316<\/span> \u67e5\u770b\u5168\u6587 »<\/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":0,"uagb_excerpt":"1. \u4ec0\u4e48\u662fMySQL\u6d3e\u751f\u8868\uff1f \u6d3e\u751f\u8868\uff08Derived Table\uff09\uff0c\u662f\u590d\u6742SQL\u5728\u6267\u884c\u8fc7\u7a0b\u4e2d\u7684\u4e2d\u95f4\u8868\uff0c\u4e5f\u53ef\u8ba4…","_links":{"self":[{"href":"http:\/\/www.weijing.co\/index.php?rest_route=\/wp\/v2\/posts\/1952"}],"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=1952"}],"version-history":[{"count":0,"href":"http:\/\/www.weijing.co\/index.php?rest_route=\/wp\/v2\/posts\/1952\/revisions"}],"wp:attachment":[{"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1952"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1952"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1952"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}