{"id":106765,"date":"2026-09-18T09:48:59","date_gmt":"2026-09-18T01:48:59","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/106765.html"},"modified":"2026-09-18T09:48:59","modified_gmt":"2026-09-18T01:48:59","slug":"mysql-dql%e5%85%a8%e9%9d%a2%e8%a7%a3%e6%9e%90%ef%bc%9a%e4%bb%8e%e5%85%a5%e9%97%a8%e5%88%b0%e7%b2%be%e9%80%9a","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/106765.html","title":{"rendered":"MySQL DQL\u5168\u9762\u89e3\u6790\uff1a\u4ece\u5165\u95e8\u5230\u7cbe\u901a"},"content":{"rendered":"

\u200b\"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

\u5728\u6570\u636e\u5e93\u7684\u5e7f\u9614\u5929\u5730\u4e2d，MySQL \u51ed\u501f\u5176\u5f00\u6e90\u3001\u9ad8\u6548\u3001\u6613\u7528\u7b49\u7279\u6027，\u6210\u4e3a\u4e86\u4f17\u591a\u5f00\u53d1\u8005\u7684\u9996\u9009\u3002\u800c\u5728 MySQL \u7684\u4f17\u591a\u529f\u80fd\u4e2d，\u6570\u636e\u67e5\u8be2\u8bed\u8a00（Data Query Language，\u7b80\u79f0 DQL）\u65e0\u7591\u662f\u6700\u4e3a\u5e38\u7528\u4e14\u5f3a\u5927\u7684\u90e8\u5206\u4e4b\u4e00\u3002\u901a\u8fc7 DQL，\u6211\u4eec\u53ef\u4ee5\u4ece\u6570\u636e\u5e93\u4e2d\u68c0\u7d22\u51fa\u6240\u9700\u7684\u6570\u636e，\u8fdb\u884c\u5404\u79cd\u590d\u6742\u7684\u6570\u636e\u5206\u6790\u548c\u5904\u7406\u3002\u672c\u6587\u5c06\u6df1\u5165\u63a2\u8ba8 MySQL DQL \u7684\u5404\u4e2a\u65b9\u9762，\u5e2e\u52a9\u4f60\u5168\u9762\u638c\u63e1\u8fd9\u4e00\u91cd\u8981\u6280\u80fd\u3002<\/p>\n

\u4e00\u3001DQL \u57fa\u7840：SELECT \u8bed\u53e5\u5165\u95e8<\/h4>\n

DQL \u7684\u6838\u5fc3\u662f SELECT \u8bed\u53e5，\u5b83\u7684\u57fa\u672c\u8bed\u6cd5\u5982\u4e0b：<\/p>\n

SELECT<\/span> column1,<\/span> column2,<\/span> .<\/span>.<\/span>.<\/span>
\nFROM<\/span> table_name;<\/span><\/p>\n

\u5176\u4e2d，SELECT\u5173\u952e\u5b57\u6307\u5b9a\u8981\u67e5\u8be2\u7684\u5217，FROM\u5173\u952e\u5b57\u6307\u5b9a\u6570\u636e\u6765\u6e90\u7684\u8868\u3002\u4f8b\u5982，\u5047\u8bbe\u6709\u4e00\u4e2a\u540d\u4e3aemployees\u7684\u8868，\u5305\u542bemployee_id\u3001first_name\u3001last_name\u548csalary\u7b49\u5217，\u8981\u67e5\u8be2\u6240\u6709\u5458\u5de5\u7684\u59d3\u540d\u548c\u85aa\u6c34，\u53ef\u4ee5\u8fd9\u6837\u5199：<\/p>\n

SELECT<\/span> first_name,<\/span> last_name,<\/span> salary
\nFROM<\/span> employees;<\/span><\/p>\n

\u5982\u679c\u8981\u67e5\u8be2\u8868\u4e2d\u7684\u6240\u6709\u5217，\u53ef\u4ee5\u4f7f\u7528\u901a\u914d\u7b26*：<\/p>\n

SELECT<\/span> *<\/span>
\nFROM<\/span> employees;<\/span><\/p>\n

\u4e0d\u8fc7，\u5728\u5b9e\u9645\u5e94\u7528\u4e2d，\u5c3d\u91cf\u660e\u786e\u6307\u5b9a\u6240\u9700\u5217，\u8fd9\u6837\u4e0d\u4ec5\u53ef\u4ee5\u63d0\u9ad8\u67e5\u8be2\u6548\u7387，\u8fd8\u80fd\u4f7f\u4ee3\u7801\u66f4\u5177\u53ef\u8bfb\u6027\u3002<\/p>\n

\u4e8c\u3001\u6570\u636e\u8fc7\u6ee4：WHERE \u5b50\u53e5\u7684\u4f7f\u7528<\/h4>\n

\u5728\u5f88\u591a\u60c5\u51b5\u4e0b，\u6211\u4eec\u5e76\u4e0d\u9700\u8981\u67e5\u8be2\u8868\u4e2d\u7684\u6240\u6709\u6570\u636e，\u800c\u662f\u5e0c\u671b\u6839\u636e\u7279\u5b9a\u6761\u4ef6\u8fdb\u884c\u7b5b\u9009\u3002\u8fd9\u65f6，\u5c31\u9700\u8981\u7528\u5230WHERE\u5b50\u53e5\u3002WHERE\u5b50\u53e5\u7528\u4e8e\u5728SELECT\u8bed\u53e5\u4e2d\u6dfb\u52a0\u6761\u4ef6，\u8fc7\u6ee4\u51fa\u7b26\u5408\u6761\u4ef6\u7684\u884c\u3002\u5176\u8bed\u6cd5\u5982\u4e0b：<\/p>\n

SELECT<\/span> column1,<\/span> column2,<\/span> .<\/span>.<\/span>.<\/span><\/p>\n

FROM<\/span> table_name<\/p>\n

WHERE<\/span> condition;<\/span><\/p>\n

condition\u662f\u4e00\u4e2a\u903b\u8f91\u8868\u8fbe\u5f0f，\u53ef\u4ee5\u4f7f\u7528\u5404\u79cd\u6bd4\u8f83\u8fd0\u7b97\u7b26（\u5982=\u3001<>\u3001<\u3001>\u3001<=\u3001>=）\u3001\u903b\u8f91\u8fd0\u7b97\u7b26（\u5982AND\u3001OR\u3001NOT）\u4ee5\u53ca\u5176\u4ed6\u51fd\u6570\u548c\u8868\u8fbe\u5f0f\u3002\u4f8b\u5982，\u8981\u67e5\u8be2\u85aa\u6c34\u5927\u4e8e 5000 \u7684\u5458\u5de5\u4fe1\u606f：<\/p>\n

SELECT<\/span> *<\/span><\/p>\n

FROM<\/span> employees<\/p>\n

WHERE<\/span> salary ><\/span> 5000<\/span>;<\/span><\/p>\n

\u8981\u67e5\u8be2\u90e8\u95e8\u4e3a \u201c\u9500\u552e\u90e8\u201d \u4e14\u85aa\u6c34\u5927\u4e8e 8000 \u7684\u5458\u5de5：<\/p>\n

SELECT<\/span> *<\/span><\/p>\n

FROM<\/span> employees<\/p>\n

WHERE<\/span> department =<\/span> '\u9500\u552e\u90e8'<\/span> AND<\/span> salary ><\/span> 8000<\/span>;<\/span><\/p>\n

WHERE\u5b50\u53e5\u8fd8\u652f\u6301\u4f7f\u7528LIKE\u5173\u952e\u5b57\u8fdb\u884c\u6a21\u7cca\u67e5\u8be2\u3002LIKE\u901a\u5e38\u4e0e\u901a\u914d\u7b26\u4e00\u8d77\u4f7f\u7528，%\u8868\u793a\u4efb\u610f\u5b57\u7b26\u5e8f\u5217（\u5305\u62ec\u7a7a\u5b57\u7b26\u5e8f\u5217），_\u8868\u793a\u4efb\u610f\u5355\u4e2a\u5b57\u7b26\u3002\u4f8b\u5982，\u8981\u67e5\u8be2\u59d3 \u201c\u5f20\u201d \u7684\u5458\u5de5：<\/p>\n

SELECT<\/span> *<\/span><\/p>\n

FROM<\/span> employees<\/p>\n

WHERE<\/span> first_name LIKE<\/span> '\u5f20%'<\/span>;<\/span><\/p>\n

\u67e5\u8be2\u540d\u5b57\u4e2d\u5305\u542b \u201c\u660e\u201d \u5b57\u7684\u5458\u5de5：<\/p>\n

SELECT<\/span> *<\/span><\/p>\n

FROM<\/span> employees<\/p>\n

WHERE<\/span> first_name LIKE<\/span> '%\u660e%'<\/span>;<\/span><\/p>\n

\u4e09\u3001\u7ed3\u679c\u6392\u5e8f：ORDER BY \u5b50\u53e5<\/h4>\n

\u67e5\u8be2\u7ed3\u679c\u9ed8\u8ba4\u662f\u65e0\u5e8f\u7684，\u4f46\u5728\u5b9e\u9645\u5e94\u7528\u4e2d，\u6211\u4eec\u5e38\u5e38\u9700\u8981\u5bf9\u7ed3\u679c\u8fdb\u884c\u6392\u5e8f，\u4ee5\u4fbf\u66f4\u597d\u5730\u67e5\u770b\u548c\u5206\u6790\u6570\u636e\u3002ORDER BY\u5b50\u53e5\u7528\u4e8e\u5bf9\u67e5\u8be2\u7ed3\u679c\u8fdb\u884c\u6392\u5e8f，\u5176\u8bed\u6cd5\u5982\u4e0b：<\/p>\n

SELECT<\/span> column1,<\/span> column2,<\/span> .<\/span>.<\/span>.<\/span><\/p>\n

FROM<\/span> table_name<\/p>\n

ORDER<\/span> BY<\/span> column1 [<\/span>ASC<\/span>|<\/span>DESC<\/span>]<\/span>,<\/span> column2 [<\/span>ASC<\/span>|<\/span>DESC<\/span>]<\/span>,<\/span> .<\/span>.<\/span>.<\/span>;<\/span><\/p>\n

ASC\u8868\u793a\u5347\u5e8f\u6392\u5217（\u9ed8\u8ba4），DESC\u8868\u793a\u964d\u5e8f\u6392\u5217\u3002\u4f8b\u5982，\u8981\u6309\u7167\u85aa\u6c34\u4ece\u9ad8\u5230\u4f4e\u67e5\u8be2\u5458\u5de5\u4fe1\u606f：<\/p>\n

SELECT<\/span> *<\/span><\/p>\n

FROM<\/span> employees<\/p>\n

ORDER<\/span> BY<\/span> salary DESC<\/span>;<\/span><\/p>\n

\u5982\u679c\u8981\u5148\u6309\u90e8\u95e8\u5347\u5e8f\u6392\u5e8f，\u5728\u6bcf\u4e2a\u90e8\u95e8\u5185\u518d\u6309\u85aa\u6c34\u964d\u5e8f\u6392\u5e8f，\u53ef\u4ee5\u8fd9\u6837\u5199：<\/p>\n

SELECT<\/span> *<\/span><\/p>\n

FROM<\/span> employees<\/p>\n

ORDER<\/span> BY<\/span> department ASC<\/span>,<\/span> salary DESC<\/span>;<\/span><\/p>\n

\u56db\u3001\u805a\u5408\u51fd\u6570：\u7edf\u8ba1\u6570\u636e\u7684\u5229\u5668<\/h4>\n

\u805a\u5408\u51fd\u6570\u7528\u4e8e\u5bf9\u4e00\u7ec4\u6570\u636e\u8fdb\u884c\u8ba1\u7b97，\u5e76\u8fd4\u56de\u4e00\u4e2a\u5355\u4e00\u7684\u503c\u3002\u5e38\u89c1\u7684\u805a\u5408\u51fd\u6570\u6709COUNT（\u8ba1\u6570）\u3001SUM（\u6c42\u548c）\u3001AVG（\u5e73\u5747\u503c）\u3001MAX（\u6700\u5927\u503c）\u548cMIN（\u6700\u5c0f\u503c）\u3002\u8fd9\u4e9b\u51fd\u6570\u5728\u6570\u636e\u5206\u6790\u4e2d\u975e\u5e38\u6709\u7528\u3002<\/p>\n

  • COUNT \u51fd\u6570：\u7528\u4e8e\u7edf\u8ba1\u6ee1\u8db3\u6761\u4ef6\u7684\u884c\u6570\u3002\u4f8b\u5982，\u8981\u7edf\u8ba1\u5458\u5de5\u8868\u4e2d\u7684\u5458\u5de5\u603b\u6570：<\/li>\n

    SELECT<\/span> COUNT<\/span>(<\/span>*<\/span>)<\/span><\/p>\n

    FROM<\/span> employees;<\/span><\/p>\n

    \u8981\u7edf\u8ba1\u85aa\u6c34\u5927\u4e8e 6000 \u7684\u5458\u5de5\u4eba\u6570：<\/p>\n

    SELECT<\/span> COUNT<\/span>(<\/span>*<\/span>)<\/span><\/p>\n

    FROM<\/span> employees<\/p>\n

    WHERE<\/span> salary ><\/span> 6000<\/span>;<\/span><\/p>\n

  • SUM \u51fd\u6570：\u7528\u4e8e\u8ba1\u7b97\u67d0\u4e00\u5217\u7684\u603b\u548c\u3002\u4f8b\u5982，\u8981\u8ba1\u7b97\u6240\u6709\u5458\u5de5\u7684\u85aa\u6c34\u603b\u548c：<\/li>\n

    SELECT<\/span> SUM<\/span>(<\/span>salary)<\/span><\/p>\n

    FROM<\/span> employees;<\/span><\/p>\n

  • AVG \u51fd\u6570：\u7528\u4e8e\u8ba1\u7b97\u67d0\u4e00\u5217\u7684\u5e73\u5747\u503c\u3002\u4f8b\u5982，\u8981\u8ba1\u7b97\u5458\u5de5\u7684\u5e73\u5747\u85aa\u6c34：<\/li>\n

    SELECT<\/span> AVG<\/span>(<\/span>salary)<\/span><\/p>\n

    FROM<\/span> employees;<\/span><\/p>\n

  • MAX \u548c MIN \u51fd\u6570：\u5206\u522b\u7528\u4e8e\u83b7\u53d6\u67d0\u4e00\u5217\u7684\u6700\u5927\u503c\u548c\u6700\u5c0f\u503c\u3002\u4f8b\u5982，\u8981\u83b7\u53d6\u6700\u9ad8\u85aa\u6c34\u548c\u6700\u4f4e\u85aa\u6c34：<\/li>\n

    SELECT<\/span> MAX<\/span>(<\/span>salary)<\/span>,<\/span> MIN<\/span>(<\/span>salary)<\/span><\/p>\n

    FROM<\/span> employees;<\/span><\/p>\n

    \u4e94\u3001\u5206\u7ec4\u67e5\u8be2：GROUP BY \u5b50\u53e5\u4e0e HAVING \u5b50\u53e5<\/p>\n

    \u5f53\u6211\u4eec\u9700\u8981\u5bf9\u6570\u636e\u8fdb\u884c\u5206\u7ec4\u7edf\u8ba1\u65f6，\u5c31\u9700\u8981\u7528\u5230GROUP BY\u5b50\u53e5\u3002GROUP BY\u5b50\u53e5\u5c06\u67e5\u8be2\u7ed3\u679c\u6309\u7167\u6307\u5b9a\u7684\u5217\u8fdb\u884c\u5206\u7ec4，\u7136\u540e\u53ef\u4ee5\u5bf9\u6bcf\u4e2a\u7ec4\u5e94\u7528\u805a\u5408\u51fd\u6570\u3002\u5176\u8bed\u6cd5\u5982\u4e0b：<\/p>\n

    SELECT<\/span> column1,<\/span> aggregate_function(<\/span>column2)<\/span><\/p>\n

    FROM<\/span> table_name<\/p>\n

    GROUP<\/span> BY<\/span> column1;<\/span><\/p>\n

    \u4f8b\u5982，\u8981\u6309\u90e8\u95e8\u7edf\u8ba1\u5458\u5de5\u4eba\u6570：<\/p>\n

    SELECT<\/span> department,<\/span> COUNT<\/span>(<\/span>*<\/span>)<\/span><\/p>\n

    FROM<\/span> employees<\/p>\n

    GROUP<\/span> BY<\/span> department;<\/span><\/p>\n

    \u5982\u679c\u5728\u5206\u7ec4\u540e\u8fd8\u9700\u8981\u5bf9\u7ec4\u8fdb\u884c\u8fc7\u6ee4，\u5c31\u9700\u8981\u4f7f\u7528HAVING\u5b50\u53e5\u3002HAVING\u5b50\u53e5\u7684\u4f5c\u7528\u7c7b\u4f3c\u4e8eWHERE\u5b50\u53e5，\u4f46WHERE\u5b50\u53e5\u7528\u4e8e\u5bf9\u884c\u8fdb\u884c\u8fc7\u6ee4，\u800cHAVING\u5b50\u53e5\u7528\u4e8e\u5bf9\u7ec4\u8fdb\u884c\u8fc7\u6ee4\u3002\u4f8b\u5982，\u8981\u67e5\u8be2\u5458\u5de5\u4eba\u6570\u5927\u4e8e 5 \u7684\u90e8\u95e8：<\/p>\n

    SELECT<\/span> department,<\/span> COUNT<\/span>(<\/span>*<\/span>)<\/span><\/p>\n

    FROM<\/span> employees<\/p>\n

    GROUP<\/span> BY<\/span> department<\/p>\n

    HAVING<\/span> COUNT<\/span>(<\/span>*<\/span>)<\/span> ><\/span> 5<\/span>;<\/span><\/p>\n

    \u516d\u3001\u8fde\u63a5\u67e5\u8be2：\u6574\u5408\u591a\u8868\u6570\u636e<\/h4>\n

    \u5728\u5b9e\u9645\u7684\u6570\u636e\u5e93\u5e94\u7528\u4e2d，\u6570\u636e\u5f80\u5f80\u5206\u6563\u5728\u591a\u4e2a\u8868\u4e2d\u3002\u8fde\u63a5\u67e5\u8be2\u5141\u8bb8\u6211\u4eec\u4ece\u591a\u4e2a\u8868\u4e2d\u68c0\u7d22\u6570\u636e，\u5e76\u5c06\u5b83\u4eec\u7ec4\u5408\u5728\u4e00\u8d77\u3002\u5e38\u89c1\u7684\u8fde\u63a5\u7c7b\u578b\u6709\u5185\u8fde\u63a5（INNER JOIN）\u3001\u5de6\u8fde\u63a5（LEFT JOIN）\u3001\u53f3\u8fde\u63a5（RIGHT JOIN）\u548c\u5168\u8fde\u63a5（FULL JOIN，MySQL \u4e0d\u76f4\u63a5\u652f\u6301，\u53ef\u901a\u8fc7LEFT JOIN\u548cRIGHT JOIN\u8054\u5408\u5b9e\u73b0）\u3002<\/p>\n

  • \u5185\u8fde\u63a5（INNER JOIN）：\u8fd4\u56de\u4e24\u4e2a\u8868\u4e2d\u6ee1\u8db3\u8fde\u63a5\u6761\u4ef6\u7684\u6240\u6709\u884c\u3002\u5176\u8bed\u6cd5\u5982\u4e0b：<\/li>\n

    SELECT<\/span> column1,<\/span> column2,<\/span> .<\/span>.<\/span>.<\/span><\/p>\n

    FROM<\/span> table1<\/p>\n

    INNER<\/span> JOIN<\/span> table2<\/p>\n

    ON<\/span> table1.<\/span>common_column =<\/span> table2.<\/span>common_column;<\/span><\/p>\n

    \u4f8b\u5982，\u5047\u8bbe\u6709\u4e00\u4e2adepartments\u8868，\u5305\u542bdepartment_id\u548cdepartment_name\u5217，\u8981\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u53ca\u5176\u5458\u5de5\u4fe1\u606f，\u53ef\u4ee5\u4f7f\u7528\u5185\u8fde\u63a5：<\/p>\n

    SELECT<\/span> employees.<\/span>employee_id,<\/span> employees.<\/span>first_name,<\/span> departments.<\/span>department_name<\/p>\n

    FROM<\/span> employees<\/p>\n

    INNER<\/span> JOIN<\/span> departments<\/p>\n

    ON<\/span> employees.<\/span>department_id =<\/span> departments.<\/span>department_id;<\/span><\/p>\n

  • \u5de6\u8fde\u63a5（LEFT JOIN）：\u8fd4\u56de\u5de6\u8868\u4e2d\u7684\u6240\u6709\u884c\u4ee5\u53ca\u53f3\u8868\u4e2d\u6ee1\u8db3\u8fde\u63a5\u6761\u4ef6\u7684\u884c\u3002\u5982\u679c\u53f3\u8868\u4e2d\u6ca1\u6709\u5339\u914d\u7684\u884c，\u5219\u7ed3\u679c\u96c6\u4e2d\u76f8\u5e94\u5217\u7684\u503c\u4e3aNULL\u3002\u8bed\u6cd5\u5982\u4e0b：<\/li>\n

    SELECT<\/span> column1,<\/span> column2,<\/span> .<\/span>.<\/span>.<\/span><\/p>\n

    FROM<\/span> table1<\/p>\n

    LEFT<\/span> JOIN<\/span> table2<\/p>\n

    ON<\/span> table1.<\/span>common_column =<\/span> table2.<\/span>common_column;<\/span><\/p>\n

    \u4f8b\u5982，\u8981\u67e5\u8be2\u6240\u6709\u90e8\u95e8\u53ca\u5176\u5458\u5de5\u4fe1\u606f，\u5373\u4f7f\u67d0\u4e2a\u90e8\u95e8\u6ca1\u6709\u5458\u5de5，\u4e5f\u8981\u663e\u793a\u8be5\u90e8\u95e8\u4fe1\u606f，\u53ef\u4ee5\u4f7f\u7528\u5de6\u8fde\u63a5：<\/p>\n

    SELECT<\/span> departments.<\/span>department_name,<\/span> employees.<\/span>employee_id,<\/span> employees.<\/span>first_name<\/p>\n

    FROM<\/span> departments<\/p>\n

    LEFT<\/span> JOIN<\/span> employees<\/p>\n

    ON<\/span> departments.<\/span>department_id =<\/span> employees.<\/span>department_id;<\/span><\/p>\n

  • \u53f3\u8fde\u63a5（RIGHT JOIN）：\u4e0e\u5de6\u8fde\u63a5\u76f8\u53cd，\u8fd4\u56de\u53f3\u8868\u4e2d\u7684\u6240\u6709\u884c\u4ee5\u53ca\u5de6\u8868\u4e2d\u6ee1\u8db3\u8fde\u63a5\u6761\u4ef6\u7684\u884c\u3002\u8bed\u6cd5\u5982\u4e0b：<\/li>\n

    SELECT<\/span> column1,<\/span> column2,<\/span> .<\/span>.<\/span>.<\/span><\/p>\n

    FROM<\/span> table1<\/p>\n

    RIGHT<\/span> JOIN<\/span> table2<\/p>\n

    ON<\/span> table1.<\/span>common_column =<\/span> table2.<\/span>common_column;<\/span><\/p>\n

    \u5728\u5b9e\u9645\u5e94\u7528\u4e2d，\u6839\u636e\u5177\u4f53\u9700\u6c42\u9009\u62e9\u5408\u9002\u7684\u8fde\u63a5\u7c7b\u578b\u975e\u5e38\u91cd\u8981，\u5b83\u76f4\u63a5\u5f71\u54cd\u5230\u67e5\u8be2\u7ed3\u679c\u7684\u51c6\u786e\u6027\u548c\u5b8c\u6574\u6027\u3002<\/p>\n

    \u4e03\u3001\u5b50\u67e5\u8be2：\u67e5\u8be2\u4e2d\u7684\u67e5\u8be2<\/h4>\n

    \u5b50\u67e5\u8be2\u662f\u6307\u5728\u4e00\u4e2a\u67e5\u8be2\u8bed\u53e5\u4e2d\u5d4c\u5957\u53e6\u4e00\u4e2a\u67e5\u8be2\u8bed\u53e5\u3002\u5b50\u67e5\u8be2\u53ef\u4ee5\u5d4c\u5957\u5728SELECT\u3001FROM\u3001WHERE\u7b49\u5b50\u53e5\u4e2d，\u7528\u4e8e\u89e3\u51b3\u4e00\u4e9b\u590d\u6742\u7684\u67e5\u8be2\u9700\u6c42\u3002\u4f8b\u5982，\u8981\u67e5\u8be2\u85aa\u6c34\u9ad8\u4e8e\u5e73\u5747\u85aa\u6c34\u7684\u5458\u5de5：<\/p>\n

    SELECT<\/span> *<\/span><\/p>\n

    FROM<\/span> employees<\/p>\n

    WHERE<\/span> salary ><\/span> (<\/span>SELECT<\/span> AVG<\/span>(<\/span>salary)<\/span> FROM<\/span> employees)<\/span>;<\/span><\/p>\n

    \u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d，\u5b50\u67e5\u8be2(SELECT AVG(salary) FROM employees)\u5148\u8ba1\u7b97\u51fa\u5e73\u5747\u85aa\u6c34，\u7136\u540e\u4e3b\u67e5\u8be2\u6839\u636e\u8fd9\u4e2a\u7ed3\u679c\u7b5b\u9009\u51fa\u85aa\u6c34\u9ad8\u4e8e\u5e73\u5747\u85aa\u6c34\u7684\u5458\u5de5\u3002<\/p>\n

    \u5b50\u67e5\u8be2\u8fd8\u53ef\u4ee5\u7528\u4e8e\u591a\u8868\u5173\u8054\u7684\u590d\u6742\u67e5\u8be2\u573a\u666f\u3002\u4f8b\u5982，\u5047\u8bbe\u6709\u4e00\u4e2aorders\u8868\u8bb0\u5f55\u8ba2\u5355\u4fe1\u606f，\u5305\u542border_id\u3001customer_id\u548corder_amount\u5217，\u8981\u67e5\u8be2\u8d2d\u4e70\u91d1\u989d\u6700\u9ad8\u7684\u5ba2\u6237\u4fe1\u606f，\u53ef\u4ee5\u8fd9\u6837\u5199：<\/p>\n

    SELECT<\/span> *<\/span><\/p>\n

    FROM<\/span> customers<\/p>\n

    WHERE<\/span> customer_id =<\/span> (<\/span>SELECT<\/span> customer_id<\/p>\n

    FROM<\/span> orders<\/p>\n

    ORDER<\/span> BY<\/span> order_amount DESC<\/span><\/p>\n

    LIMIT<\/span> 1<\/span>)<\/span>;<\/span><\/p>\n

    \u8fd9\u91cc，\u5b50\u67e5\u8be2\u5148\u627e\u51fa\u8d2d\u4e70\u91d1\u989d\u6700\u9ad8\u7684\u8ba2\u5355\u5bf9\u5e94\u7684\u5ba2\u6237 ID，\u7136\u540e\u4e3b\u67e5\u8be2\u6839\u636e\u8fd9\u4e2a ID \u67e5\u8be2\u5ba2\u6237\u4fe1\u606f\u3002<\/p>\n

    \u516b\u3001DQL \u5b9e\u6218\u6280\u5de7\u4e0e\u4f18\u5316<\/h4>\n
  • \u4f7f\u7528\u7d22\u5f15：\u7d22\u5f15\u662f\u63d0\u9ad8\u67e5\u8be2\u6027\u80fd\u7684\u91cd\u8981\u624b\u6bb5\u3002\u5728\u7ecf\u5e38\u7528\u4e8e\u67e5\u8be2\u6761\u4ef6\u7684\u5217\u4e0a\u521b\u5efa\u7d22\u5f15，\u53ef\u4ee5\u663e\u8457\u52a0\u5feb\u67e5\u8be2\u901f\u5ea6\u3002\u4f8b\u5982，\u5982\u679c\u7ecf\u5e38\u6839\u636e\u5458\u5de5\u7684employee_id\u8fdb\u884c\u67e5\u8be2，\u53ef\u4ee5\u5728employee_id\u5217\u4e0a\u521b\u5efa\u7d22\u5f15：<\/li>\n

    CREATE<\/span> INDEX<\/span> idx_employee_id ON<\/span> employees(<\/span>employee_id)<\/span>;<\/span><\/p>\n

    \u4f46\u8981\u6ce8\u610f，\u7d22\u5f15\u5e76\u4e0d\u662f\u8d8a\u591a\u8d8a\u597d，\u8fc7\u591a\u7684\u7d22\u5f15\u4f1a\u589e\u52a0\u6570\u636e\u63d2\u5165\u3001\u66f4\u65b0\u548c\u5220\u9664\u7684\u65f6\u95f4，\u56e0\u4e3a\u6570\u636e\u5e93\u5728\u66f4\u65b0\u6570\u636e\u65f6，\u8fd8\u9700\u8981\u540c\u65f6\u66f4\u65b0\u7d22\u5f15\u3002<\/p>\n

    2. \u907f\u514d\u5168\u8868\u626b\u63cf：\u5c3d\u91cf\u907f\u514d\u5728\u67e5\u8be2\u4e2d\u4f7f\u7528\u6ca1\u6709\u7d22\u5f15\u7684\u5217\u8fdb\u884c\u8fc7\u6ee4\u6761\u4ef6，\u4ee5\u514d\u5bfc\u81f4\u5168\u8868\u626b\u63cf\u3002\u4f8b\u5982，\u5982\u679cemployees\u8868\u7684email\u5217\u6ca1\u6709\u7d22\u5f15，\u800c\u67e5\u8be2\u8bed\u53e5\u4e3aSELECT * FROM employees WHERE email = '``example@example.com``';，\u6570\u636e\u5e93\u5c31\u9700\u8981\u626b\u63cf\u6574\u4e2a\u8868\u6765\u67e5\u627e\u5339\u914d\u7684\u884c，\u8fd9\u5728\u6570\u636e\u91cf\u8f83\u5927\u65f6\u4f1a\u975e\u5e38\u8017\u65f6\u3002<\/p>\n

    3. \u4f18\u5316\u5b50\u67e5\u8be2：\u5b50\u67e5\u8be2\u867d\u7136\u5f3a\u5927，\u4f46\u5982\u679c\u4f7f\u7528\u4e0d\u5f53，\u53ef\u80fd\u4f1a\u5bfc\u81f4\u6027\u80fd\u95ee\u9898\u3002\u5728\u4e00\u4e9b\u60c5\u51b5\u4e0b，\u53ef\u4ee5\u5c06\u5b50\u67e5\u8be2\u6539\u5199\u4e3a\u8fde\u63a5\u67e5\u8be2，\u4ee5\u63d0\u9ad8\u6027\u80fd\u3002\u4f8b\u5982，\u524d\u9762\u63d0\u5230\u7684\u67e5\u8be2\u85aa\u6c34\u9ad8\u4e8e\u5e73\u5747\u85aa\u6c34\u7684\u5458\u5de5\u7684\u4f8b\u5b50，\u4e5f\u53ef\u4ee5\u6539\u5199\u4e3a\u8fde\u63a5\u67e5\u8be2：<\/p>\n

    SELECT<\/span> e1.<\/span>*<\/span><\/p>\n

    FROM<\/span> employees e1<\/p>\n

    JOIN<\/span> (<\/span>SELECT<\/span> AVG<\/span>(<\/span>salary)<\/span> AS<\/span> avg_salary FROM<\/span> employees)<\/span> e2<\/p>\n

    ON<\/span> e1.<\/span>salary ><\/span> e2.<\/span>avg_salary;<\/span><\/p>\n

  • \u5408\u7406\u4f7f\u7528\u4e34\u65f6\u8868\u548c\u89c6\u56fe：\u5728\u5904\u7406\u590d\u6742\u67e5\u8be2\u65f6，\u53ef\u4ee5\u8003\u8651\u4f7f\u7528\u4e34\u65f6\u8868\u548c\u89c6\u56fe\u3002\u4e34\u65f6\u8868\u7528\u4e8e\u5b58\u50a8\u4e2d\u95f4\u7ed3\u679c，\u5728\u9700\u8981\u591a\u6b21\u4f7f\u7528\u8fd9\u4e9b\u7ed3\u679c\u65f6，\u53ef\u4ee5\u51cf\u5c11\u91cd\u590d\u8ba1\u7b97\u3002\u89c6\u56fe\u5219\u53ef\u4ee5\u5c06\u590d\u6742\u7684\u67e5\u8be2\u5c01\u88c5\u8d77\u6765，\u65b9\u4fbf\u540e\u7eed\u5f15\u7528，\u540c\u65f6\u4e5f\u63d0\u9ad8\u4e86\u6570\u636e\u7684\u5b89\u5168\u6027\u548c\u4e00\u81f4\u6027\u3002\u4f8b\u5982，\u521b\u5efa\u4e00\u4e2a\u89c6\u56fe\u6765\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u5458\u5de5\u4eba\u6570\u548c\u5e73\u5747\u85aa\u6c34：<\/li>\n

    CREATE<\/span> VIEW<\/span> department_summary AS<\/span><\/p>\n

    SELECT<\/span> department,<\/span> COUNT<\/span>(<\/span>*<\/span>)<\/span> AS<\/span> employee\\\\_count,<\/span> AVG<\/span>(<\/span>salary)<\/span> AS<\/span> avg_salary<\/p>\n

    FROM<\/span> employees<\/p>\n

    GROUP<\/span> BY<\/span> department;<\/span><\/p>\n

    \u4e4b\u540e，\u53ef\u4ee5\u50cf\u67e5\u8be2\u666e\u901a\u8868\u4e00\u6837\u67e5\u8be2\u8fd9\u4e2a\u89c6\u56fe：<\/p>\n

    SELECT<\/span> *<\/span> FROM<\/span> department_summary;<\/span><\/p>\n

    \u4e5d\u3001\u603b\u7ed3<\/h4>\n

    MySQL DQL \u4f5c\u4e3a\u6570\u636e\u5e93\u67e5\u8be2\u7684\u6838\u5fc3\u5de5\u5177，\u5177\u6709\u4e30\u5bcc\u7684\u529f\u80fd\u548c\u5f3a\u5927\u7684\u8868\u73b0\u529b\u3002\u901a\u8fc7\u672c\u6587\u7684\u4ecb\u7ecd，\u4f60\u5df2\u7ecf\u4e86\u89e3\u4e86 DQL \u7684\u57fa\u7840\u8bed\u6cd5\u3001\u5e38\u7528\u5b50\u53e5\u3001\u9ad8\u7ea7\u5e94\u7528\u4ee5\u53ca\u5b9e\u6218\u4f18\u5316\u6280\u5de7\u3002\u5728\u5b9e\u9645\u5e94\u7528\u4e2d，\u4e0d\u65ad\u7ec3\u4e60\u548c\u79ef\u7d2f\u7ecf\u9a8c，\u6839\u636e\u5177\u4f53\u7684\u4e1a\u52a1\u9700\u6c42\u7075\u6d3b\u8fd0\u7528\u8fd9\u4e9b\u77e5\u8bc6，\u4f60\u5c06\u80fd\u591f\u9ad8\u6548\u5730\u4ece\u6570\u636e\u5e93\u4e2d\u83b7\u53d6\u6240\u9700\u7684\u6570\u636e，\u4e3a\u6570\u636e\u5206\u6790\u3001\u4e1a\u52a1\u51b3\u7b56\u7b49\u63d0\u4f9b\u6709\u529b\u652f\u6301\u3002<\/p>\n

    \u5e0c\u671b\u672c\u6587\u80fd\u6210\u4e3a\u4f60\u5b66\u4e60 MySQL DQL \u7684\u5f97\u529b\u52a9\u624b，\u5e2e\u52a9\u4f60\u5728\u6570\u636e\u5e93\u5f00\u53d1\u7684\u9053\u8def\u4e0a\u8fc8\u51fa\u575a\u5b9e\u7684\u6b65\u4f10\u3002\u5982\u679c\u4f60\u5728\u5b66\u4e60\u8fc7\u7a0b\u4e2d\u9047\u5230\u95ee\u9898，\u4e0d\u8981\u6c14\u9981，\u591a\u67e5\u9605\u8d44\u6599，\u591a\u5b9e\u8df5，\u76f8\u4fe1\u4f60\u4e00\u5b9a\u80fd\u591f\u638c\u63e1\u8fd9\u95e8\u91cd\u8981\u7684\u6280\u80fd\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"

    \u200b
    \n\u5728\u6570\u636e\u5e93\u7684\u5e7f\u9614\u5929\u5730\u4e2d，MySQL \u51ed\u501f\u5176\u5f00\u6e90\u3001\u9ad8\u6548\u3001\u6613\u7528\u7b49\u7279\u6027，\u6210\u4e3a\u4e86\u4f17\u591a\u5f00\u53d1\u8005\u7684\u9996\u9009\u3002\u800c\u5728 MySQL \u7684\u4f17\u591a\u529f\u80fd\u4e2d，\u6570\u636e\u67e5\u8be2\u8bed\u8a00（Data Query Language，\u7b80\u79f0 DQL）\u65e0\u7591\u662f\u6700\u4e3a\u5e38\u7528\u4e14\u5f3a\u5927\u7684\u90e8\u5206\u4e4b\u4e00\u3002\u901a\u8fc7 DQL，\u6211\u4eec\u53ef\u4ee5\u4ece\u6570\u636e\u5e93\u4e2d\u68c0\u7d22\u51fa\u6240\u9700\u7684\u6570\u636e，\u8fdb\u884c\u5404\u79cd\u590d\u6742\u7684\u6570\u636e\u5206\u6790\u548c\u5904\u7406\u3002\u672c\u6587\u5c06\u6df1\u5165\u63a2\u8ba8 MySQL DQL \u7684\u5404\u4e2a\u65b9\u9762，\u5e2e<\/p>\n","protected":false},"author":2,"featured_media":106764,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[12124,114,768,100],"topic":[],"class_list":["post-106765","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-server","tag-dql","tag-mysql","tag-sql","tag-100"],"yoast_head":"\nMySQL DQL\u5168\u9762\u89e3\u6790\uff1a\u4ece\u5165\u95e8\u5230\u7cbe\u901a - 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