{"id":2688,"date":"2025-03-12T23:48:28","date_gmt":"2025-03-12T15:48:28","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=2688"},"modified":"2025-03-12T23:48:28","modified_gmt":"2025-03-12T15:48:28","slug":"postgresql-%e5%ad%90%e6%9f%a5%e8%af%a2%ef%bc%88subquery%ef%bc%89%e8%af%a6%e8%a7%a3","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/03\/12\/postgresql-%e5%ad%90%e6%9f%a5%e8%af%a2%ef%bc%88subquery%ef%bc%89%e8%af%a6%e8%a7%a3\/","title":{"rendered":"PostgreSQL \u5b50\u67e5\u8be2\uff08Subquery\uff09\u8be6\u89e3"},"content":{"rendered":"\n

\u5b50\u67e5\u8be2<\/strong>\uff08Subquery\uff09\u662f\u5d4c\u5957\u5728\u53e6\u4e00\u4e2a\u67e5\u8be2\uff08\u5982 SELECT<\/code>\u3001INSERT<\/code>\u3001UPDATE<\/code> \u6216 DELETE<\/code>\uff09\u4e2d\u7684\u67e5\u8be2\u3002\u5b50\u67e5\u8be2\u53ef\u4ee5\u5728\u6570\u636e\u5e93\u4e2d\u5145\u5f53\u4e00\u4e2a\u4e34\u65f6\u7684\u8868\uff0c\u63d0\u4f9b\u67e5\u8be2\u7684\u6570\u636e\u3002PostgreSQL \u652f\u6301\u591a\u79cd\u7c7b\u578b\u7684\u5b50\u67e5\u8be2\uff0c\u5305\u62ec\u6807\u91cf\u5b50\u67e5\u8be2\u3001\u5217\u5b50\u67e5\u8be2\u3001\u884c\u5b50\u67e5\u8be2\u548c\u8fde\u63a5\u5b50\u67e5\u8be2\u7b49\u3002<\/p>\n\n\n\n

\n\n\n\n

1. \u5b50\u67e5\u8be2\u7684\u57fa\u672c\u7528\u6cd5<\/strong><\/h2>\n\n\n\n

\u5b50\u67e5\u8be2\u901a\u5e38\u7528\u4e8e\u4ee5\u4e0b\u51e0\u79cd\u60c5\u5f62\uff1a<\/p>\n\n\n\n

    \n
  • \u4f5c\u4e3a\u67e5\u8be2\u6761\u4ef6<\/strong>\uff1a\u5b50\u67e5\u8be2\u53ef\u4ee5\u4f5c\u4e3a WHERE<\/code>\u3001HAVING<\/code> \u6216 FROM<\/code> \u5b50\u53e5\u7684\u6761\u4ef6\uff0c\u7528\u4e8e\u7b5b\u9009\u6570\u636e\u3002<\/li>\n\n\n\n
  • \u4f5c\u4e3a\u4e34\u65f6\u8868<\/strong>\uff1a\u5b50\u67e5\u8be2\u53ef\u4ee5\u4f5c\u4e3a\u4e00\u4e2a\u865a\u62df\u8868\uff0c\u5728 FROM<\/code> \u5b50\u53e5\u4e2d\u4f7f\u7528\u3002<\/li>\n<\/ul>\n\n\n\n
    \n\n\n\n

    2. \u5b50\u67e5\u8be2\u7684\u7c7b\u578b<\/strong><\/h2>\n\n\n\n

    2.1 \u6807\u91cf\u5b50\u67e5\u8be2\uff08Scalar Subquery\uff09<\/strong><\/h3>\n\n\n\n

    \u6807\u91cf\u5b50\u67e5\u8be2\u8fd4\u56de\u4e00\u4e2a\u5355\u4e00\u503c\uff0c\u901a\u5e38\u5728\u67e5\u8be2\u7684 SELECT<\/code>\u3001WHERE<\/code> \u6216 HAVING<\/code> \u5b50\u53e5\u4e2d\u4f7f\u7528\u3002<\/p>\n\n\n\n

    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n

    SELECT name, salary\nFROM employees\nWHERE salary > (\n    SELECT AVG(salary)\n    FROM employees\n);<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1a\u8fd9\u4e2a\u67e5\u8be2\u9009\u62e9\u6240\u6709\u5de5\u8d44\u9ad8\u4e8e\u5458\u5de5\u5e73\u5747\u5de5\u8d44\u7684\u5458\u5de5\u3002\u5b50\u67e5\u8be2 (SELECT AVG(salary) FROM employees)<\/code> \u8ba1\u7b97\u5458\u5de5\u7684\u5e73\u5747\u5de5\u8d44\uff0c\u6807\u91cf\u5b50\u67e5\u8be2\u7684\u7ed3\u679c\u662f\u4e00\u4e2a\u5355\u4e00\u503c\uff0c\u7528\u6765\u4e0e\u5916\u90e8\u67e5\u8be2\u7684\u5de5\u8d44\u8fdb\u884c\u6bd4\u8f83\u3002<\/p>\n\n\n\n
    2.2 \u5217\u5b50\u67e5\u8be2\uff08Column Subquery\uff09<\/strong><\/h3>\n\n\n\n
    \u5217\u5b50\u67e5\u8be2\u8fd4\u56de\u591a\u4e2a\u503c\uff0c\u4f46\u53ea\u5305\u542b\u4e00\u4e2a\u5217\u3002\u5b83\u901a\u5e38\u7528\u4e8e IN<\/code> \u6216 NOT IN<\/code> \u5b50\u53e5\u4e2d\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n
    SELECT name, department\nFROM employees\nWHERE department IN (\n    SELECT department\n    FROM employees\n    WHERE salary > 50000\n);<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1a\u8be5\u67e5\u8be2\u67e5\u627e\u6240\u6709\u5de5\u8d44\u9ad8\u4e8e 50000 \u7684\u5458\u5de5\u6240\u5728\u90e8\u95e8\u4e2d\u7684\u5176\u4ed6\u5458\u5de5\u3002\u5b50\u67e5\u8be2\u8fd4\u56de\u4e00\u4e2a\u90e8\u95e8\u5217\u8868\uff0c\u5916\u90e8\u67e5\u8be2\u901a\u8fc7 IN<\/code> \u5b50\u53e5\u4f7f\u7528\u8be5\u5217\u8868\u6765\u7b5b\u9009\u5458\u5de5\u3002<\/p>\n\n\n\n
    2.3 \u884c\u5b50\u67e5\u8be2\uff08Row Subquery\uff09<\/strong><\/h3>\n\n\n\n
    \u884c\u5b50\u67e5\u8be2\u8fd4\u56de\u591a\u5217\u548c\u591a\u884c\uff0c\u901a\u5e38\u7528\u4e8e\u6bd4\u8f83\u591a\u4e2a\u5217\u7684\u503c\u3002\u5b83\u901a\u5e38\u4e0e IN<\/code>\u3001ANY<\/code> \u6216 ALL<\/code> \u4e00\u8d77\u4f7f\u7528\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n
    SELECT name, department, salary\nFROM employees\nWHERE (department, salary) IN (\n    SELECT department, MAX(salary)\n    FROM employees\n    GROUP BY department\n);<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1a\u6b64\u67e5\u8be2\u67e5\u627e\u6bcf\u4e2a\u90e8\u95e8\u4e2d\u5de5\u8d44\u6700\u9ad8\u7684\u5458\u5de5\u3002\u5b50\u67e5\u8be2\u8fd4\u56de\u6bcf\u4e2a\u90e8\u95e8\u7684\u6700\u5927\u5de5\u8d44\uff0c\u5916\u90e8\u67e5\u8be2\u6839\u636e\u90e8\u95e8\u548c\u5de5\u8d44\u5339\u914d\u5458\u5de5\u4fe1\u606f\u3002<\/p>\n\n\n\n
    2.4 \u76f8\u5173\u5b50\u67e5\u8be2\uff08Correlated Subquery\uff09<\/strong><\/h3>\n\n\n\n
    \u76f8\u5173\u5b50\u67e5\u8be2\u4e0e\u5916\u90e8\u67e5\u8be2\u7684\u6bcf\u4e00\u884c\u76f8\u5173\u8054\u3002\u5b83\u901a\u8fc7\u5916\u90e8\u67e5\u8be2\u7684\u5217\u4e0e\u5b50\u67e5\u8be2\u7684\u5217\u8fdb\u884c\u6bd4\u8f83\uff0c\u6267\u884c\u65f6\u4e3a\u6bcf\u4e00\u884c\u8ba1\u7b97\u5b50\u67e5\u8be2\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n
    SELECT e1.name, e1.salary\nFROM employees e1\nWHERE e1.salary > (\n    SELECT AVG(e2.salary)\n    FROM employees e2\n    WHERE e1.department = e2.department\n);<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1a\u6b64\u67e5\u8be2\u67e5\u627e\u6bcf\u4e2a\u90e8\u95e8\u4e2d\u5de5\u8d44\u9ad8\u4e8e\u8be5\u90e8\u95e8\u5e73\u5747\u5de5\u8d44\u7684\u5458\u5de5\u3002\u5b50\u67e5\u8be2\u4f9d\u8d56\u4e8e\u5916\u90e8\u67e5\u8be2\u7684 department<\/code> \u5217\uff0c\u56e0\u6b64\u5b83\u662f\u4e00\u4e2a\u76f8\u5173\u5b50\u67e5\u8be2\u3002<\/p>\n\n\n\n
    \n\n\n\n
    3. \u5b50\u67e5\u8be2\u7684\u4f7f\u7528\u573a\u666f<\/strong><\/h2>\n\n\n\n
    3.1 \u5b50\u67e5\u8be2\u4f5c\u4e3a SELECT<\/code> \u7684\u4e00\u90e8\u5206<\/strong><\/h3>\n\n\n\n
    \u5b50\u67e5\u8be2\u53ef\u4ee5\u4f5c\u4e3a\u5916\u90e8\u67e5\u8be2\u7684\u5217\u8fd4\u56de\u503c\u4e4b\u4e00\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n
    SELECT name, (\n    SELECT department\n    FROM employees\n    WHERE employees.id = employees_department.id\n) AS department\nFROM employees_department;<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1a\u6b64\u67e5\u8be2\u4ece employees_department<\/code> \u8868\u4e2d\u9009\u62e9\u5458\u5de5\u7684\u540d\u5b57\uff0c\u5e76\u4e14\u4e3a\u6bcf\u4e2a\u5458\u5de5\u8fd4\u56de\u5176\u6240\u5728\u7684\u90e8\u95e8\u3002<\/p>\n\n\n\n
    3.2 \u5b50\u67e5\u8be2\u4f5c\u4e3a FROM<\/code> \u5b50\u53e5\u7684\u4e00\u90e8\u5206<\/strong><\/h3>\n\n\n\n
    \u5b50\u67e5\u8be2\u53ef\u4ee5\u4f5c\u4e3a FROM<\/code> \u5b50\u53e5\u4e2d\u7684\u8868\uff0c\u901a\u5e38\u7528\u6765\u521b\u5efa\u4e34\u65f6\u8868\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n
    SELECT sub.department, sub.avg_salary\nFROM (\n    SELECT department, AVG(salary) AS avg_salary\n    FROM employees\n    GROUP BY department\n) AS sub;<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1a\u8be5\u67e5\u8be2\u9996\u5148\u901a\u8fc7\u5b50\u67e5\u8be2\u8ba1\u7b97\u6bcf\u4e2a\u90e8\u95e8\u7684\u5e73\u5747\u5de5\u8d44\uff0c\u7136\u540e\u5728\u5916\u90e8\u67e5\u8be2\u4e2d\u83b7\u53d6\u8fd9\u4e9b\u7ed3\u679c\u3002<\/p>\n\n\n\n
    3.3 \u5b50\u67e5\u8be2\u4f5c\u4e3a WHERE<\/code> \u5b50\u53e5\u7684\u4e00\u90e8\u5206<\/strong><\/h3>\n\n\n\n
    \u5b50\u67e5\u8be2\u5e38\u5e38\u4e0e WHERE<\/code> \u5b50\u53e5\u914d\u5408\u4f7f\u7528\uff0c\u7528\u6765\u7b5b\u9009\u6570\u636e\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n
    SELECT name, salary\nFROM employees\nWHERE department = 'HR'\n  AND salary > (\n    SELECT AVG(salary)\n    FROM employees\n    WHERE department = 'HR'\n);<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1a\u67e5\u8be2\u627e\u51fa HR<\/code> \u90e8\u95e8\u4e2d\u5de5\u8d44\u9ad8\u4e8e\u90e8\u95e8\u5e73\u5747\u5de5\u8d44\u7684\u5458\u5de5\u3002<\/p>\n\n\n\n
    3.4 \u5b50\u67e5\u8be2\u4f5c\u4e3a HAVING<\/code> \u5b50\u53e5\u7684\u4e00\u90e8\u5206<\/strong><\/h3>\n\n\n\n
    \u5b50\u67e5\u8be2\u4e5f\u53ef\u4ee5\u5728 HAVING<\/code> \u5b50\u53e5\u4e2d\u4f7f\u7528\uff0c\u4ee5\u7b5b\u9009\u5206\u7ec4\u540e\u7684\u6570\u636e\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n
    SELECT department, COUNT(*) AS employee_count\nFROM employees\nGROUP BY department\nHAVING COUNT(*) > (\n    SELECT AVG(employee_count)\n    FROM (\n        SELECT department, COUNT(*) AS employee_count\n        FROM employees\n        GROUP BY department\n    ) AS dept_counts\n);<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1a\u8be5\u67e5\u8be2\u8fd4\u56de\u5458\u5de5\u6570\u591a\u4e8e\u6240\u6709\u90e8\u95e8\u5e73\u5747\u5458\u5de5\u6570\u7684\u90e8\u95e8\u3002<\/p>\n\n\n\n
    \n\n\n\n
    4. \u5b50\u67e5\u8be2\u6027\u80fd\u4f18\u5316<\/strong><\/h2>\n\n\n\n
    \u5b50\u67e5\u8be2\u5728\u6267\u884c\u65f6\u53ef\u80fd\u9700\u8981\u591a\u6b21\u626b\u63cf\u8868\uff0c\u7279\u522b\u662f\u76f8\u5173\u5b50\u67e5\u8be2\u548c\u5927\u578b\u6570\u636e\u96c6\u65f6\uff0c\u53ef\u80fd\u4f1a\u5f71\u54cd\u67e5\u8be2\u6027\u80fd\u3002\u4ee5\u4e0b\u662f\u4e00\u4e9b\u4f18\u5316\u5b50\u67e5\u8be2\u7684\u65b9\u6cd5\uff1a<\/p>\n\n\n\n
    4.1 \u4f7f\u7528\u8fde\u63a5\u4ee3\u66ff\u5b50\u67e5\u8be2<\/strong><\/h3>\n\n\n\n
    \u5bf9\u4e8e\u67d0\u4e9b\u5b50\u67e5\u8be2\uff0c\u5c24\u5176\u662f\u975e\u76f8\u5173\u5b50\u67e5\u8be2\uff0c\u53ef\u4ee5\u901a\u8fc7\u8fde\u63a5\uff08JOIN<\/code>\uff09\u6765\u66ff\u4ee3\uff0c\u901a\u5e38\u80fd\u63d0\u9ad8\u6027\u80fd\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n
    SELECT e1.name, e1.salary\nFROM employees e1\nJOIN (\n    SELECT department, MAX(salary) AS max_salary\n    FROM employees\n    GROUP BY department\n) e2\nON e1.department = e2.department\nWHERE e1.salary = e2.max_salary;<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1a\u8fd9\u4e2a\u67e5\u8be2\u4f7f\u7528\u8fde\u63a5\u4ee3\u66ff\u5b50\u67e5\u8be2\uff0c\u901a\u5e38\u6bd4\u76f4\u63a5\u4f7f\u7528\u5b50\u67e5\u8be2\u6267\u884c\u5f97\u66f4\u5feb\u3002<\/p>\n\n\n\n
    4.2 \u4f7f\u7528 EXISTS \u4ee3\u66ff IN<\/strong><\/h3>\n\n\n\n
    \u5728\u5904\u7406\u5177\u6709\u8f83\u5927\u96c6\u5408\u7684\u6570\u636e\u65f6\uff0c\u4f7f\u7528 EXISTS<\/code> \u66ff\u4ee3 IN<\/code> \u5b50\u67e5\u8be2\u53ef\u80fd\u4f1a\u66f4\u9ad8\u6548\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a<\/strong><\/p>\n\n\n\n
    SELECT name\nFROM employees e1\nWHERE EXISTS (\n    SELECT 1\n    FROM employees e2\n    WHERE e1.department = e2.department\n      AND e2.salary > 50000\n);<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>\uff1aEXISTS<\/code> \u5b50\u67e5\u8be2\u5728\u627e\u5230\u7b2c\u4e00\u4e2a\u7b26\u5408\u6761\u4ef6\u7684\u8bb0\u5f55\u65f6\u7acb\u5373\u505c\u6b62\uff0c\u8fd9\u6bd4 IN<\/code> \u5b50\u67e5\u8be2\uff08\u4f1a\u5c06\u6240\u6709\u5339\u914d\u503c\u52a0\u8f7d\u5230\u5185\u5b58\u4e2d\uff09\u901a\u5e38\u66f4\u9ad8\u6548\u3002<\/p>\n\n\n\n
    \n\n\n\n
    5. \u603b\u7ed3<\/strong><\/h2>\n\n\n\n
    PostgreSQL \u4e2d\u7684\u5b50\u67e5\u8be2\u63d0\u4f9b\u4e86\u5f3a\u5927\u7684\u67e5\u8be2\u529f\u80fd\uff0c\u80fd\u8ba9\u4f60\u5728\u67e5\u8be2\u4e2d\u52a8\u6001\u8ba1\u7b97\u3001\u7b5b\u9009\u548c\u805a\u5408\u6570\u636e\u3002\u901a\u8fc7\u9002\u5f53\u5730\u9009\u62e9\u4e0d\u540c\u7c7b\u578b\u7684\u5b50\u67e5\u8be2\uff08\u5982\u6807\u91cf\u5b50\u67e5\u8be2\u3001\u5217\u5b50\u67e5\u8be2\u3001\u884c\u5b50\u67e5\u8be2\u7b49\uff09\uff0c\u4f60\u53ef\u4ee5\u7075\u6d3b\u5730\u5904\u7406\u5404\u79cd\u67e5\u8be2\u9700\u6c42\u3002\u540c\u65f6\uff0c\u7406\u89e3\u5e76\u5e94\u7528\u4f18\u5316\u6280\u672f\uff0c\u53ef\u4ee5\u663e\u8457\u63d0\u5347\u67e5\u8be2\u6027\u80fd\u3002<\/p>\n\n\n\n
    \u66f4\u591a\u8be6\u7ec6\u5185\u5bb9\u8bf7\u5173\u6ce8\u5176\u4ed6\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"
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