{"id":160659,"date":"2024-11-03T23:56:23","date_gmt":"2024-11-03T15:56:23","guid":{"rendered":"https:\/\/server.hk\/cnblog\/160659\/"},"modified":"2024-11-03T23:56:24","modified_gmt":"2024-11-03T15:56:24","slug":"postgresql%e6%95%99%e7%a8%8bpostgresql-%e5%b8%b8%e7%94%a8%e5%87%bd%e6%95%b8","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/160659\/","title":{"rendered":"POSTGRESQL\u6559\u7a0bPostgreSQL \u5e38\u7528\u51fd\u6578"},"content":{"rendered":"<h1 id=\"postgresql-%e5%b8%b8%e7%94%a8%e5%87%bd%e6%95%b8%e6%95%99%e7%a8%8b-lfGwZzTAsr\">PostgreSQL \u5e38\u7528\u51fd\u6578\u6559\u7a0b<\/h1>\n<p>PostgreSQL \u662f\u4e00\u500b\u529f\u80fd\u5f37\u5927\u7684\u958b\u6e90\u95dc\u806f\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\uff0c\u5ee3\u6cdb\u61c9\u7528\u65bc\u5404\u7a2e\u61c9\u7528\u7a0b\u5e8f\u4e2d\u3002\u5b83\u63d0\u4f9b\u4e86\u8a31\u591a\u5167\u5efa\u7684\u51fd\u6578\uff0c\u9019\u4e9b\u51fd\u6578\u53ef\u4ee5\u5e6b\u52a9\u7528\u6236\u66f4\u6709\u6548\u5730\u8655\u7406\u6578\u64da\u3002\u672c\u6587\u5c07\u4ecb\u7d39\u4e00\u4e9b PostgreSQL \u4e2d\u5e38\u7528\u7684\u51fd\u6578\uff0c\u4e26\u63d0\u4f9b\u76f8\u61c9\u7684\u793a\u4f8b\uff0c\u4ee5\u5e6b\u52a9\u8b80\u8005\u66f4\u597d\u5730\u7406\u89e3\u548c\u4f7f\u7528\u9019\u4e9b\u51fd\u6578\u3002<\/p>\n<h2 id=\"1-%e5%ad%97%e7%ac%a6%e4%b8%b2%e5%87%bd%e6%95%b8-lfGwZzTAsr\">1. \u5b57\u7b26\u4e32\u51fd\u6578<\/h2>\n<p>\u5b57\u7b26\u4e32\u51fd\u6578\u5728\u6578\u64da\u8655\u7406\u4e2d\u975e\u5e38\u91cd\u8981\uff0c\u4ee5\u4e0b\u662f\u4e00\u4e9b\u5e38\u7528\u7684\u5b57\u7b26\u4e32\u51fd\u6578\uff1a<\/p>\n<ul>\n<li><code>LENGTH(string)<\/code>\uff1a\u8fd4\u56de\u5b57\u7b26\u4e32\u7684\u9577\u5ea6\u3002<\/li>\n<li><code>UPPER(string)<\/code>\uff1a\u5c07\u5b57\u7b26\u4e32\u8f49\u63db\u70ba\u5927\u5beb\u3002<\/li>\n<li><code>LOWER(string)<\/code>\uff1a\u5c07\u5b57\u7b26\u4e32\u8f49\u63db\u70ba\u5c0f\u5beb\u3002<\/li>\n<li><code>SUBSTRING(string FROM start FOR length)<\/code>\uff1a\u63d0\u53d6\u5b57\u7b26\u4e32\u7684\u4e00\u90e8\u5206\u3002<\/li>\n<\/ul>\n<p>\u4f8b\u5982\uff0c\u4ee5\u4e0b\u67e5\u8a62\u5c07\u8fd4\u56de\u5b57\u7b26\u4e32 &#8220;Hello World&#8221; \u7684\u9577\u5ea6\uff1a<\/p>\n<pre><code>SELECT LENGTH('Hello World');<\/code><\/pre>\n<h2 id=\"2-%e6%95%b8%e5%ad%b8%e5%87%bd%e6%95%b8-lfGwZzTAsr\">2. \u6578\u5b78\u51fd\u6578<\/h2>\n<p>PostgreSQL \u63d0\u4f9b\u4e86\u591a\u7a2e\u6578\u5b78\u51fd\u6578\uff0c\u9019\u4e9b\u51fd\u6578\u53ef\u4ee5\u7528\u65bc\u6578\u503c\u8a08\u7b97\uff1a<\/p>\n<ul>\n<li><code>ABS(value)<\/code>\uff1a\u8fd4\u56de\u6578\u503c\u7684\u7d55\u5c0d\u503c\u3002<\/li>\n<li><code>ROUND(value, decimal_places)<\/code>\uff1a\u5c07\u6578\u503c\u56db\u6368\u4e94\u5165\u5230\u6307\u5b9a\u7684\u5c0f\u6578\u4f4d\u6578\u3002<\/li>\n<li><code>CEIL(value)<\/code>\uff1a\u8fd4\u56de\u5927\u65bc\u6216\u7b49\u65bc\u6307\u5b9a\u6578\u503c\u7684\u6700\u5c0f\u6574\u6578\u3002<\/li>\n<li><code>FLOOR(value)<\/code>\uff1a\u8fd4\u56de\u5c0f\u65bc\u6216\u7b49\u65bc\u6307\u5b9a\u6578\u503c\u7684\u6700\u5927\u6574\u6578\u3002<\/li>\n<\/ul>\n<p>\u4f8b\u5982\uff0c\u4ee5\u4e0b\u67e5\u8a62\u5c07\u8a08\u7b97 -10 \u7684\u7d55\u5c0d\u503c\uff1a<\/p>\n<pre><code>SELECT ABS(-10);<\/code><\/pre>\n<h2 id=\"3-%e6%97%a5%e6%9c%9f%e5%92%8c%e6%99%82%e9%96%93%e5%87%bd%e6%95%b8-lfGwZzTAsr\">3. \u65e5\u671f\u548c\u6642\u9593\u51fd\u6578<\/h2>\n<p>\u65e5\u671f\u548c\u6642\u9593\u51fd\u6578\u5728\u8655\u7406\u6642\u9593\u6233\u548c\u65e5\u671f\u6642\u975e\u5e38\u6709\u7528\uff1a<\/p>\n<ul>\n<li><code>NOW()<\/code>\uff1a\u8fd4\u56de\u7576\u524d\u7684\u65e5\u671f\u548c\u6642\u9593\u3002<\/li>\n<li><code>AGE(timestamp1, timestamp2)<\/code>\uff1a\u8a08\u7b97\u5169\u500b\u6642\u9593\u6233\u4e4b\u9593\u7684\u5dee\u7570\u3002<\/li>\n<li><code>DATE_PART('field', source)<\/code>\uff1a\u63d0\u53d6\u65e5\u671f\u6216\u6642\u9593\u7684\u7279\u5b9a\u90e8\u5206\u3002<\/li>\n<\/ul>\n<p>\u4f8b\u5982\uff0c\u4ee5\u4e0b\u67e5\u8a62\u5c07\u8fd4\u56de\u7576\u524d\u7684\u65e5\u671f\u548c\u6642\u9593\uff1a<\/p>\n<pre><code>SELECT NOW();<\/code><\/pre>\n<h2 id=\"4-%e8%81%9a%e5%90%88%e5%87%bd%e6%95%b8-lfGwZzTAsr\">4. \u805a\u5408\u51fd\u6578<\/h2>\n<p>\u805a\u5408\u51fd\u6578\u7528\u65bc\u5c0d\u6578\u64da\u9032\u884c\u8a08\u7b97\uff0c\u4e26\u8fd4\u56de\u55ae\u4e00\u7684\u7d50\u679c\uff1a<\/p>\n<ul>\n<li><code>COUNT(column)<\/code>\uff1a\u8a08\u7b97\u884c\u6578\u3002<\/li>\n<li><code>SUM(column)<\/code>\uff1a\u8a08\u7b97\u6578\u503c\u7684\u7e3d\u548c\u3002<\/li>\n<li><code>AVG(column)<\/code>\uff1a\u8a08\u7b97\u6578\u503c\u7684\u5e73\u5747\u503c\u3002<\/li>\n<li><code>MAX(column)<\/code>\uff1a\u8fd4\u56de\u5217\u4e2d\u7684\u6700\u5927\u503c\u3002<\/li>\n<li><code>MIN(column)<\/code>\uff1a\u8fd4\u56de\u5217\u4e2d\u7684\u6700\u5c0f\u503c\u3002<\/li>\n<\/ul>\n<p>\u4f8b\u5982\uff0c\u4ee5\u4e0b\u67e5\u8a62\u5c07\u8a08\u7b97\u67d0\u500b\u8868\u4e2d\u6240\u6709\u884c\u7684\u6578\u91cf\uff1a<\/p>\n<pre><code>SELECT COUNT(*) FROM your_table;<\/code><\/pre>\n<h2 id=\"5-%e6%a2%9d%e4%bb%b6%e5%87%bd%e6%95%b8-lfGwZzTAsr\">5. \u689d\u4ef6\u51fd\u6578<\/h2>\n<p>\u689d\u4ef6\u51fd\u6578\u53ef\u4ee5\u6839\u64da\u7279\u5b9a\u689d\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u7d50\u679c\uff1a<\/p>\n<ul>\n<li><code>CASE<\/code>\uff1a\u6839\u64da\u689d\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u503c\u3002<\/li>\n<li><code>COALESCE(value1, value2, ...)<\/code>\uff1a\u8fd4\u56de\u7b2c\u4e00\u500b\u975e\u7a7a\u503c\u3002<\/li>\n<\/ul>\n<p>\u4f8b\u5982\uff0c\u4ee5\u4e0b\u67e5\u8a62\u4f7f\u7528 CASE \u51fd\u6578\u4f86\u6839\u64da\u5206\u6578\u8fd4\u56de\u8a55\u7d1a\uff1a<\/p>\n<pre><code>SELECT \n    CASE \n        WHEN score &gt;= 90 THEN 'A'\n        WHEN score &gt;= 80 THEN 'B'\n        ELSE 'C'\n    END AS grade\nFROM students;<\/code><\/pre>\n<h2 id=\"%e7%b8%bd%e7%b5%90-lfGwZzTAsr\">\u7e3d\u7d50<\/h2>\n<p>PostgreSQL \u63d0\u4f9b\u4e86\u591a\u7a2e\u5f37\u5927\u7684\u51fd\u6578\uff0c\u9019\u4e9b\u51fd\u6578\u53ef\u4ee5\u5e6b\u52a9\u7528\u6236\u5728\u6578\u64da\u8655\u7406\u548c\u5206\u6790\u4e2d\u63d0\u9ad8\u6548\u7387\u3002\u7121\u8ad6\u662f\u5b57\u7b26\u4e32\u8655\u7406\u3001\u6578\u5b78\u8a08\u7b97\u3001\u65e5\u671f\u6642\u9593\u64cd\u4f5c\u9084\u662f\u6578\u64da\u805a\u5408\uff0c\u638c\u63e1\u9019\u4e9b\u5e38\u7528\u51fd\u6578\u90fd\u80fd\u4f7f\u958b\u767c\u8005\u5728\u4f7f\u7528 PostgreSQL \u6642\u66f4\u52a0\u5f97\u5fc3\u61c9\u624b\u3002\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u9ad8\u6548\u7684 <a href=\"https:\/\/server.hk\">VPS<\/a> \u89e3\u6c7a\u65b9\u6848\u4f86\u904b\u884c PostgreSQL\uff0cServer.HK \u63d0\u4f9b\u4e86\u591a\u7a2e\u9078\u64c7\uff0c\u6eff\u8db3\u60a8\u7684\u9700\u6c42\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5b66\u4e60PostgreSQL\u5e38\u7528\u51fd\u6570\uff0c\u901a\u8fc7\u5b9e\u7528\u6559\u7a0b\u638c\u63e1\u6570\u636e\u5904\u7406\u3001\u67e5\u8be2\u4f18\u5316\u548c\u6027\u80fd\u63d0\u5347\u6280\u5de7\uff0c\u63d0\u5347\u6570\u636e\u5e93\u7ba1\u7406\u80fd\u529b\u3002<\/p>\n","protected":false},"author":0,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-160659","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/160659","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=160659"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/160659\/revisions"}],"predecessor-version":[{"id":160660,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/160659\/revisions\/160660"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=160659"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=160659"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=160659"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}