{"id":60325,"date":"2024-10-13T01:55:15","date_gmt":"2024-10-12T17:55:15","guid":{"rendered":"https:\/\/server.hk\/cnblog\/60325\/"},"modified":"2024-10-13T01:55:16","modified_gmt":"2024-10-12T17:55:16","slug":"db2-select%e8%aa%9e%e5%8f%a5%e9%ab%98%e7%b4%9a%e7%94%a8%e6%b3%95%e5%af%a6%e4%be%8b%e6%bc%94%e7%a4%ba","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/60325\/","title":{"rendered":"DB2 SELECT\u8a9e\u53e5\u9ad8\u7d1a\u7528\u6cd5\u5be6\u4f8b\u6f14\u793a"},"content":{"rendered":"

DB2 SELECT\u8a9e\u53e5\u9ad8\u7d1a\u7528\u6cd5\u5be6\u4f8b\u6f14\u793a<\/h1>\n

\u5728\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0cDB2\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u5ee3\u6cdb\u61c9\u7528\u65bc\u4f01\u696d\u7d1a\u61c9\u7528\u7a0b\u5e8f\u4e2d\u3002\u5176SELECT\u8a9e\u53e5\u662f\u7528\u65bc\u67e5\u8a62\u6578\u64da\u7684\u6838\u5fc3\u529f\u80fd\u4e4b\u4e00\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eDB2 SELECT\u8a9e\u53e5\u7684\u9ad8\u7d1a\u7528\u6cd5\uff0c\u4e26\u901a\u904e\u5be6\u4f8b\u6f14\u793a\u5176\u5f37\u5927\u529f\u80fd\u3002<\/p>\n

1. \u57fa\u672cSELECT\u8a9e\u53e5<\/h2>\n

\u5728\u958b\u59cb\u9ad8\u7d1a\u7528\u6cd5\u4e4b\u524d\uff0c\u9996\u5148\u56de\u9867\u4e00\u4e0b\u57fa\u672c\u7684SELECT\u8a9e\u53e5\u3002\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n

SELECT column1, column2 FROM table_name WHERE condition;<\/code><\/pre>\n
\u4f8b\u5982\uff0c\u5f9e\u540d\u70ba\u201cemployees\u201d\u7684\u8868\u4e2d\u9078\u64c7\u6240\u6709\u54e1\u5de5\u7684\u59d3\u540d\u548c\u5de5\u8cc7\uff1a<\/p>\n
SELECT name, salary FROM employees;<\/code><\/pre>\n
2. \u4f7f\u7528\u805a\u5408\u51fd\u6578<\/h2>\n
\u805a\u5408\u51fd\u6578\u5982COUNT\u3001SUM\u3001AVG\u3001MAX\u548cMIN\u53ef\u4ee5\u7528\u4f86\u5c0d\u6578\u64da\u9032\u884c\u7d71\u8a08\u5206\u6790\u3002\u4ee5\u4e0b\u662f\u4f7f\u7528\u805a\u5408\u51fd\u6578\u7684\u793a\u4f8b\uff1a<\/p>\n
SELECT COUNT(*) AS total_employees FROM employees;<\/code><\/pre>\n
\u9019\u689d\u8a9e\u53e5\u5c07\u8fd4\u56de\u201cemployees\u201d\u8868\u4e2d\u7684\u7e3d\u54e1\u5de5\u6578\u3002<\/p>\n
2.1 GROUP BY\u5b50\u53e5<\/h3>\n
\u7576\u9700\u8981\u5c0d\u6578\u64da\u9032\u884c\u5206\u7d44\u6642\uff0c\u53ef\u4ee5\u4f7f\u7528GROUP BY\u5b50\u53e5\u3002\u4f8b\u5982\uff0c\u8a08\u7b97\u6bcf\u500b\u90e8\u9580\u7684\u5e73\u5747\u5de5\u8cc7\uff1a<\/p>\n
SELECT department, AVG(salary) AS avg_salary FROM employees GROUP BY department;<\/code><\/pre>\n
3. \u4f7f\u7528JOIN\u64cd\u4f5c<\/h2>\n
JOIN\u64cd\u4f5c\u5141\u8a31\u5f9e\u591a\u500b\u8868\u4e2d\u67e5\u8a62\u6578\u64da\u3002\u4ee5\u4e0b\u662fINNER JOIN\u7684\u793a\u4f8b\uff1a<\/p>\n
SELECT e.name, d.department_name \nFROM employees e \nINNER JOIN departments d ON e.department_id = d.id;<\/code><\/pre>\n
\u9019\u689d\u8a9e\u53e5\u5c07\u8fd4\u56de\u6bcf\u4f4d\u54e1\u5de5\u53ca\u5176\u6240\u5c6c\u90e8\u9580\u7684\u540d\u7a31\u3002<\/p>\n
3.1 LEFT JOIN\u548cRIGHT JOIN<\/h3>\n
LEFT JOIN\u548cRIGHT JOIN\u7528\u65bc\u7372\u53d6\u4e00\u500b\u8868\u4e2d\u7684\u6240\u6709\u8a18\u9304\uff0c\u5373\u4f7f\u5728\u53e6\u4e00\u500b\u8868\u4e2d\u6c92\u6709\u5339\u914d\u7684\u8a18\u9304\u3002\u4f8b\u5982\uff0c\u4f7f\u7528LEFT JOIN\u67e5\u8a62\u6240\u6709\u54e1\u5de5\u53ca\u5176\u90e8\u9580\uff0c\u5373\u4f7f\u67d0\u4e9b\u54e1\u5de5\u6c92\u6709\u90e8\u9580\uff1a<\/p>\n
SELECT e.name, d.department_name \nFROM employees e \nLEFT JOIN departments d ON e.department_id = d.id;<\/code><\/pre>\n
4. \u4f7f\u7528\u5b50\u67e5\u8a62<\/h2>\n
\u5b50\u67e5\u8a62\u662f\u5d4c\u5957\u5728\u5176\u4ed6\u67e5\u8a62\u4e2d\u7684\u67e5\u8a62\u3002\u4ee5\u4e0b\u662f\u4f7f\u7528\u5b50\u67e5\u8a62\u7684\u793a\u4f8b\uff1a<\/p>\n
SELECT name \nFROM employees \nWHERE salary > (SELECT AVG(salary) FROM employees);<\/code><\/pre>\n
\u9019\u689d\u8a9e\u53e5\u5c07\u8fd4\u56de\u6240\u6709\u5de5\u8cc7\u9ad8\u65bc\u5e73\u5747\u5de5\u8cc7\u7684\u54e1\u5de5\u59d3\u540d\u3002<\/p>\n
5. \u4f7f\u7528CASE\u8a9e\u53e5<\/h2>\n
CASE\u8a9e\u53e5\u5141\u8a31\u5728\u67e5\u8a62\u4e2d\u9032\u884c\u689d\u4ef6\u908f\u8f2f\u8655\u7406\u3002\u4ee5\u4e0b\u662f\u4f7f\u7528CASE\u7684\u793a\u4f8b\uff1a<\/p>\n
SELECT name, \n       CASE \n           WHEN salary < 30000 THEN '\u4f4e' \n           WHEN salary BETWEEN 30000 AND 60000 THEN '\u4e2d' \n           ELSE '\u9ad8' \n       END AS salary_level \nFROM employees;<\/code><\/pre>\n
\u9019\u689d\u8a9e\u53e5\u5c07\u6839\u64da\u5de5\u8cc7\u6c34\u5e73\u70ba\u6bcf\u4f4d\u54e1\u5de5\u5206\u914d\u4e00\u500b\u6a19\u7c64\u3002<\/p>\n
6. \u4f7f\u7528\u7a97\u53e3\u51fd\u6578<\/h2>\n
\u7a97\u53e3\u51fd\u6578\u5141\u8a31\u5728\u67e5\u8a62\u7d50\u679c\u4e2d\u9032\u884c\u66f4\u8907\u96dc\u7684\u8a08\u7b97\u3002\u4ee5\u4e0b\u662f\u4f7f\u7528\u7a97\u53e3\u51fd\u6578\u7684\u793a\u4f8b\uff1a<\/p>\n
SELECT name, salary, \n       RANK() OVER (ORDER BY salary DESC) AS salary_rank \nFROM employees;<\/code><\/pre>\n
\u9019\u689d\u8a9e\u53e5\u5c07\u70ba\u6bcf\u4f4d\u54e1\u5de5\u6839\u64da\u5de5\u8cc7\u6392\u540d\u3002<\/p>\n
\u7e3d\u7d50<\/h2>\n
DB2\u7684SELECT\u8a9e\u53e5\u63d0\u4f9b\u4e86\u591a\u7a2e\u9ad8\u7d1a\u7528\u6cd5\uff0c\u80fd\u5920\u6eff\u8db3\u8907\u96dc\u7684\u6578\u64da\u67e5\u8a62\u9700\u6c42\u3002\u901a\u904e\u4f7f\u7528\u805a\u5408\u51fd\u6578\u3001JOIN\u64cd\u4f5c\u3001\u5b50\u67e5\u8a62\u3001CASE\u8a9e\u53e5\u548c\u7a97\u53e3\u51fd\u6578\uff0c\u958b\u767c\u8005\u53ef\u4ee5\u9748\u6d3b\u5730\u5f9e\u6578\u64da\u5eab\u4e2d\u63d0\u53d6\u6240\u9700\u7684\u4fe1\u606f\u3002\u9019\u4e9b\u6280\u8853\u4e0d\u50c5\u63d0\u9ad8\u4e86\u67e5\u8a62\u7684\u6548\u7387\uff0c\u9084\u589e\u5f37\u4e86\u6578\u64da\u5206\u6790\u7684\u80fd\u529b\u3002<\/p>\n
\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u7a69\u5b9a\u7684 \u9999\u6e2fVPS<\/a> \u89e3\u6c7a\u65b9\u6848\u4ee5\u652f\u6301\u60a8\u7684\u6578\u64da\u5eab\u61c9\u7528\uff0cServer.HK\u63d0\u4f9b\u591a\u7a2e\u9078\u64c7\uff0c\u6eff\u8db3\u4e0d\u540c\u9700\u6c42\u3002\u7121\u8ad6\u662f\u5c0f\u578b\u4f01\u696d\u9084\u662f\u5927\u578b\u4f01\u696d\uff0c\u6211\u5011\u7684 \u4e91\u670d\u52a1\u5668<\/a> \u90fd\u80fd\u70ba\u60a8\u63d0\u4f9b\u53ef\u9760\u7684\u652f\u6301\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u63a2\u7d22DB2 SELECT\u8a9e\u53e5\u7684\u9ad8\u7d1a\u7528\u6cd5\uff0c\u901a\u904e\u5be6\u4f8b\u6f14\u793a\u6df1\u5165\u7406\u89e3\u6578\u64da\u67e5\u8a62\u6280\u5de7\uff0c\u63d0\u5347\u6578\u64da\u8655\u7406\u6548\u7387\u3002<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-60325","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/60325","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"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=60325"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/60325\/revisions"}],"predecessor-version":[{"id":60326,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/60325\/revisions\/60326"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=60325"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=60325"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=60325"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}