{"id":5376,"date":"2020-07-29T23:58:43","date_gmt":"2020-07-29T15:58:43","guid":{"rendered":"http:\/\/39.97.231.10\/?p=5376"},"modified":"2020-07-29T23:58:43","modified_gmt":"2020-07-29T15:58:43","slug":"mysql-%e9%99%8d%e5%ba%8f%e7%b4%a2%e5%bc%95-descending-indexes","status":"publish","type":"post","link":"http:\/\/www.weijing.co\/?p=5376","title":{"rendered":"MySQL \u964d\u5e8f\u7d22\u5f15 (Descending Indexes)"},"content":{"rendered":"<div>\n<div>\nMySQL 8.0 \u7248\u672c\u5f00\u59cb\u652f\u6301\u964d\u5e8f\u7d22\u5f15\uff08Descending Indexes\uff09\uff0c\u5728 8.0 \u4e4b\u524d\u7684\u7248\u672c\uff0c\u4f7f\u7528\u5173\u952e\u5b57 DESC \u5b9a\u4e49\u964d\u5e8f\u7d22\u5f15\u65f6\uff0c\u5b9e\u9645\u4e0a DESC \u662f\u88ab\u5ffd\u7565\u7684\uff0c\u4ece 8.0 \u7248\u672c\u5f00\u59cb\uff0cDESC \u5b9a\u4e49\u7684\u7d22\u5f15\uff0c\u771f\u7684\u5c31\u662f\u964d\u5e8f\u7684\u7d22\u5f15\u3002\n<\/div>\n<\/div>\n<div>\n<div>\n\u5728 8.0 \u4e4b\u524d\uff0c\u80fd\u591f\u4ee5\u76f8\u53cd\u7684\u987a\u5e8f\u5bf9\u7d22\u5f15\u8fdb\u884c\u626b\u63cf\uff0c\u4f46\u662f\u4f1a\u964d\u4f4e\u6027\u80fd\uff0c\u964d\u5e8f\u7d22\u5f15\u80fd\u591f\u5b9e\u73b0\u76f8\u540c\u7684\u6548\u679c\uff0c\u4e14\u4e0d\u4f1a\u635f\u8017\u6027\u80fd\u3002\u53e6\u5916\u4e00\u4e2a\u4f8b\u5b50\uff0c\u5f53\u4e00\u4e2a\u67e5\u8be2 SQL\uff0c\u9700\u8981\u6309\u591a\u4e2a\u5b57\u6bb5\uff0c\u4ee5\u4e0d\u540c\u7684\u987a\u5e8f\u8fdb\u884c\u6392\u5e8f\u65f6\uff0c8.0 \u4e4b\u524d\u65e0\u6cd5\u4f7f\u7528\u7d22\u5f15\u5df2\u6392\u5e8f\u7684\u7279\u6027\uff0c\u56e0\u4e3a order by \u7684\u987a\u5e8f\u4e0e\u7d22\u5f15\u7684\u987a\u5e8f\u4e0d\u4e00\u81f4\uff0c\u800c\u4f7f\u7528\u964d\u5e8f\u7d22\u5f15\uff0c\u5c31\u80fd\u591f\u6307\u5b9a\u8054\u5408\u7d22\u5f15\u4e2d\u6bcf\u4e00\u4e2a\u5b57\u6bb5\u7684\u987a\u5e8f\uff0c\u4ee5\u9002\u5e94 SQL \u8bed\u53e5\u4e2d\u7684 order by \u987a\u5e8f\uff0c\u8ba9 SQL \u80fd\u591f\u5145\u5206\u4f7f\u7528\u7d22\u5f15\u5df2\u6392\u5e8f\u7684\u7279\u6027\uff0c\u63d0\u5347 SQL \u6027\u80fd\u3002<br \/>\n\u6765\u770b\u4e00\u4e2a\u4f8b\u5b50\uff0c\u8868\u7ed3\u6784\u5982\u4e0b\uff1a<\/p>\n<pre>CREATE TABLE t (\n  c1 INT, c2 INT,\n  INDEX idx1 (c1 ASC, c2 ASC),\n  INDEX idx2 (c1 ASC, c2 DESC),\n  INDEX idx3 (c1 DESC, c2 ASC),\n  INDEX idx4 (c1 DESC, c2 DESC)\n);\n<\/pre>\n<p>\u8868\u4e2d\u6709\u4e24\u4e2a\u5b57\u6bb5\uff0cc1 \u548c c2\uff0c\u6839\u636e c1\uff0cc2 \u7684\u4e0d\u540c\u987a\u5e8f\u7684\u7ec4\u5408\uff0c\u521b\u5efa\u4e86 4 \u4e2a\u7d22\u5f15\uff0c\u7531\u4e8e\u7d22\u5f15\u5b57\u6bb5\u7684\u6392\u5e8f\u4e0d\u540c\uff0c\u56e0\u6b64\u5bf9\u4e8e\u4e0d\u540c\u7684 order by \u987a\u5e8f\uff0c\u4f18\u5316\u5668\u53ef\u4ee5\u4f7f\u7528\u7684\u7d22\u5f15\u4e5f\u4e0d\u76f8\u540c\uff0c\u5982\u679c order by \u987a\u5e8f\u4e0e\u7d22\u5f15\u5b57\u6bb5\u7684\u987a\u5e8f\u4e00\u81f4\uff0c\u90a3\u4e48\u5c31\u53ef\u4ee5\u907f\u514d\u989d\u5916\u7684 filesort\u00a0\uff0c\u4ece\u800c\u63d0\u5347\u6027\u80fd\u3002<\/p>\n<pre>ORDER BY c1 ASC, c2 ASC    -- \u4f18\u5316\u5668\u9009\u62e9\u4f7f\u7528 idx1\nORDER BY c1 DESC, c2 DESC  -- \u4f18\u5316\u5668\u9009\u62e9\u4f7f\u7528 idx4\nORDER BY c1 ASC, c2 DESC   -- \u4f18\u5316\u5668\u9009\u62e9\u4f7f\u7528 idx2\nORDER BY c1 DESC, c2 ASC   -- \u4f18\u5316\u5668\u9009\u62e9\u4f7f\u7528 idx3\n<\/pre>\n<h5>\u6dfb\u52a0\u964d\u5e8f\u7d22\u5f15\u8bed\u6cd5\uff1a<\/h5>\n<p>\u9664\u4e86\u5728\u5efa\u8868\u65f6\u521b\u5efa\u964d\u5e8f\u7d22\u5f15\u4ee5\u5916\uff0c\u8fd8\u53ef\u4ee5\u4f7f\u7528\u6539\u8868\u6dfb\u52a0\u7d22\u5f15\u7684\u8bed\u6cd5\u6765\u521b\u5efa\u964d\u5e8f\u7d22\u5f15\u3002<\/p>\n<ul>\n<li>alter table tb add index idx_1(name desc, address asc);<\/li>\n<li>create index idx_2 on tb(name desc, address desc);<\/li>\n<\/ul>\n<h5>\u964d\u5e8f\u7d22\u5f15\u7684\u9650\u5236\u6761\u4ef6\uff1a<\/h5>\n<ul>\n<li>\u53ea\u6709 InnoDB \u5b58\u50a8\u5f15\u64ce\u652f\u6301\u964d\u5e8f\u7d22\u5f15\uff0c\u5176\u4ed6\u5f15\u64ce\u4e0d\u652f\u6301\u3002<\/li>\n<li>\u5982\u679c\u4e8c\u7ea7\u7d22\u5f15\u6216\u8005\u4e3b\u952e\u7d22\u5f15\u5305\u542b\u964d\u5e8f\u5b57\u6bb5\uff0c\u90a3\u4e48 change buffer \u5c06\u4e0d\u652f\u6301\u8fd9\u6837\u7684\u7d22\u5f15\u3002<\/li>\n<li>InnoDB \u5168\u6587\u7d22\u5f15\u7684 FTS_DOC_ID\u00a0\u5b57\u6bb5\u4e0d\u80fd\u88ab\u5b9a\u4e49\u4e3a\u964d\u5e8f\u7d22\u5f15\u3002<\/li>\n<li>\u53ea\u8981\u5347\u5e8f\u7d22\u5f15\u652f\u6301\u7684\u6570\u636e\u7c7b\u578b\uff0c\u964d\u987a\u7d22\u5f15\u90fd\u652f\u6301\u3002<\/li>\n<li>\u964d\u5e8f\u7d22\u5f15\u652f\u6301\u666e\u901a\u7684\u5b57\u6bb5\u548c\u865a\u62df\u5b57\u6bb5\u3002<\/li>\n<li>\u5bf9\u4e8e\u4f7f\u7528\u805a\u5408\u51fd\u6570 max()\/min()\uff0c\u4f46\u662f\u6ca1\u6709\u4f7f\u7528 group by \u5b50\u53e5\uff0c\u4e0d\u80fd\u4f7f\u7528\u964d\u5e8f\u7d22\u5f15\u8fdb\u884c\u4f18\u5316\u3002<\/li>\n<li>\u964d\u5e8f\u7d22\u5f15\u53ea\u652f\u6301 BTREE \u7d22\u5f15\uff0c\u4e0d\u652f\u6301 HASH \u7d22\u5f15\uff0c\u540c\u6837\u4e5f\u4e0d\u652f\u6301\u5168\u6587\u7d22\u5f15\u548c\u7a7a\u95f4\u7d22\u5f15\u3002<\/li>\n<\/ul>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>MySQL 8.0 \u7248\u672c\u5f00\u59cb\u652f\u6301\u964d\u5e8f\u7d22\u5f15\uff08Descending Indexes\uff09\uff0c\u5728 8.0 \u4e4b\u524d\u7684\u7248\u672c\uff0c\u4f7f\u7528 &hellip;<\/p>\n<p class=\"read-more\"> <a class=\"\" href=\"http:\/\/www.weijing.co\/?p=5376\"> <span class=\"screen-reader-text\">MySQL \u964d\u5e8f\u7d22\u5f15 (Descending Indexes)<\/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":0,"uagb_excerpt":"MySQL 8.0 \u7248\u672c\u5f00\u59cb\u652f\u6301\u964d\u5e8f\u7d22\u5f15\uff08Descending Indexes\uff09\uff0c\u5728 8.0 \u4e4b\u524d\u7684\u7248\u672c\uff0c\u4f7f\u7528&hellip;","_links":{"self":[{"href":"http:\/\/www.weijing.co\/index.php?rest_route=\/wp\/v2\/posts\/5376"}],"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=5376"}],"version-history":[{"count":0,"href":"http:\/\/www.weijing.co\/index.php?rest_route=\/wp\/v2\/posts\/5376\/revisions"}],"wp:attachment":[{"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5376"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5376"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.weijing.co\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5376"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}