{"id":822,"date":"2022-10-10T09:37:59","date_gmt":"2022-10-10T01:37:59","guid":{"rendered":"https:\/\/qaqaq.top\/?p=822"},"modified":"2022-11-27T12:43:53","modified_gmt":"2022-11-27T04:43:53","slug":"sql%e6%b7%b1%e5%85%a5%e7%90%86%e8%a7%a3%e5%85%b3%e7%b3%bb%e4%bb%a3%e6%95%b0%e3%80%81%e7%ae%80%e5%8d%95%e6%9f%a5%e8%af%a2%e3%80%81%e8%bf%9e%e6%8e%a5","status":"publish","type":"post","link":"https:\/\/qaqaq.top\/?p=822","title":{"rendered":"SQL\u6df1\u5165\u7406\u89e3|\u5173\u7cfb\u4ee3\u6570\u3001\u7b80\u5355\u67e5\u8be2\u3001\u8fde\u63a5"},"content":{"rendered":"\n

\u672c\u6587\u601d\u7ef4\u5bfc\u56fe\uff1a<\/p>\n\n\n\n

\"\"\/<\/div>
\u601d\u7ef4\u5bfc\u56fe<\/figcaption><\/figure>\n\n\n\n

\u5173\u7cfb\u4ee3\u6570 (Relational Algebra)<\/h2>\n\n\n\n

\u5173\u7cfb\u4ee3\u6570\u662f\u6570\u636e\u5e93\u64cd\u4f5c\u7684\u6570\u5b66\u7b26\u53f7\u4f53\u7cfb\uff0c\u53ef\u4ee5\u7406\u89e3\u4e3aSQL\u7684\u6570\u5b66\u7248\u672c\u3002\u5176\u5b9e\u5e94\u8be5\u662f\u53cd\u8fc7\u6765\uff0cSQL\u662f\u5173\u7cfb\u4ee3\u6570\u7684\u5177\u4f53\u5b9e\u73b0\u3002\u7eaf\u7cb9\u7684\u6280\u672f\u4e66\u7c4d\u5f88\u5c11\u8c08\u53ca\u8fd9\u65b9\u9762\uff0c\u5e38\u5e38\u88ab\u8ba4\u4e3a\u662f\u300c\u4e66\u5377\u6c14\u592a\u6d53\u300d\u3002\u5982\u679c\u4f60\u4e0d\u559c\u6b22\u8fd9\u6837\u8fc7\u4e8e\u7406\u8bba\u7684\u63cf\u8ff0\uff0c\u53ef\u4ee5\u8df3\u8fc7\u8fd9\u4e2a\u6807\u9898\u3002\u6211\u5f3a\u70c8\u5efa\u8bae\u4f60\u4e0d\u8df3\u8fc7\uff0c\u62bd\u8c61\u7684\u63cf\u8ff0\u5e38\u5e38\u53ef\u4ee5\u5e2e\u52a9\u5efa\u7acb\u66f4\u597d\u7684\u8ba4\u77e5\u3002<\/p>\n\n\n\n

\u5173\u7cfb\u4ee3\u6570\u7684\u6240\u6709\u8bb0\u53f7\u5982\u4e0b\uff1a<\/p>\n\n\n\n

\"\"\/<\/div>
\u5173\u7cfb\u4ee3\u6570\u8bb0\u53f7<\/figcaption><\/figure>\n\n\n\n

\u5173\u7cfb\u4ee3\u6570\u8bb0\u53f7\u975e\u5e38\u6709\u9650\uff0c\u5bf9\u5e94\u7684SQL\u5173\u952e\u5b57\u4e5f\u5f88\u6709\u9650\u3002\u6709\u4e9b\u8bb0\u53f7\u5b9a\u4e49\u7684\u64cd\u4f5c\u6211\u4eec\u7ecf\u5e38\u4f7f\u7528\u4f46\u4e0d\u81ea\u77e5\uff0c\u53ef\u89c1\u8fd9\u4e9b\u64cd\u4f5c\u6709\u591a\u4e48\u7b80\u5355\uff01\u6240\u4ee5\u8981\u6709\u4fe1\u5fc3\uff0c\u4e00\u5b9a\u53ef\u4ee5\u5199\u597dSQL\uff01<\/p>\n\n\n\n

\u6bcf\u4e00\u4e2a\u8bb0\u53f7\u4ee3\u8868\u5bf9\u6570\u636e\u5e93\u7684\u4e00\u79cd\u64cd\u4f5c\uff0c\u5b9e\u73b0\u4e00\u4e2a\u6570\u636e\u5e93\uff0c\u4e5f\u5c31\u662f\u5bf9\u5e94\u5730\u628a\u8fd9\u4e9b\u64cd\u4f5c\u90fd\u5b9e\u73b0\u4e86\u3002\u4ee5\u4e0b\u4e00\u4e00\u5217\u4e3e\u3002<\/p>\n\n\n\n

\u5173\u7cfb\u6a21\u578b\u548c\u96c6\u5408 (Relational Model)<\/h2>\n\n\n\n

\u300c\u5173\u7cfb\u300d\u6a21\u578b\u662f\u975e\u5e38\u5e38\u89c1\u7684\u6570\u636e\u5e93\u8bbe\u8ba1\uff0c\u4f60\u5373\u4fbf\u4e0d\u77e5\u9053\u8fd9\u4e2a\u540d\u5b57\uff0c\u4e5f\u4e00\u5b9a\u975e\u5e38\u719f\u6089\u5b83\u7684\u6837\u5b50\u3002\u53ef\u4ee5\u7b80\u5355\u5730\u7406\u89e3\u4e3a\uff0c\u5173\u7cfb\u6a21\u578b\u5c31\u662f\u53ef\u4ee5\u753b\u6210\u4e8c\u7ef4\u8868\u683c\u7684\u6a21\u578b\u3002\u6b64\u5916\u4e0d\u5fc5\u8fc7\u591a\u89e3\u91ca\u3002<\/p>\n\n\n\n

\"\"\/<\/div>
\u7f51\u9875\u7248\u4e09\u56fd\u6740\u4f20\u5947\u6570\u636e\u8868| Mercury233<\/figcaption><\/figure>\n\n\n\n

\u6700\u9700\u8981\u6ce8\u610f\u7684\u662f\uff0c\u5173\u7cfb\u6a21\u578b\u7684\u672c\u8d28\u662f\u4e2a\u300c\u96c6\u5408\u300d\uff0c\u5176\u4e2d\u7684\u6570\u636e\u300c\u6ca1\u6709\u987a\u5e8f\u300d\uff0c\u5217\u4e4b\u95f4\u6ca1\u6709\u987a\u5e8f\uff0c\u884c\u4e4b\u95f4\u4e5f\u6ca1\u6709\u987a\u5e8f\uff0c\u53ea\u8bb2\u7a76\u300c\u5b58\u5728\u300d\u4e0e\u5426\u3002<\/p>\n\n\n\n

\u6761\u4ef6\u7b5b\u67e5\u03c3<\/h2>\n\n\n\n

\u6211\u4eec\u7ecf\u5e38\u505a\u7684\u64cd\u4f5c\u662fwhere<\/code>\uff0c\u4e5f\u5c31\u662f\u6761\u4ef6\u67e5\u8be2\u3002\u5728\u5173\u7cfb\u4ee3\u6570\u4e2d\u7684\u539f\u578b\u4e3a\u03c3pred(M)\uff0c\u8868\u793a\u5728pred<\/code>\u6761\u4ef6\u4e0b\u4ece\u96c6\u5408M\u4e2d\u4ea7\u751f\u4e00\u4e2a\u5b50\u96c6\u3002<\/p>\n\n\n\n

\u5982\u60f3\u4ece\u96c6\u5408instructor<\/code>\u4e2d\u53d6\u51fa\u5de5\u8d44salary<\/code>\u5927\u4e8e20000\u7684\u5927\u4f6c\uff0c\u5199\u6210\u5173\u7cfb\u4ee3\u6570\u5c31\u662f\u03c3salary>20000(instructor)\u3002<\/p>\n\n\n\n

\u4f60\u53ef\u80fd\u66f4\u52a0\u719f\u6089SQL\uff0c\u540c\u6837\u7684\u64cd\u4f5c\uff0c\u5199\u6210SQL\u5c31\u662fselect * from instructor where salary > 2000;<\/code><\/p>\n\n\n\n

\u9009\u62e9\u5217\u03a0<\/h2>\n\n\n\n

\u8fd9\u5e94\u8be5\u5c5e\u4e8e\u7ecf\u5e38\u4f7f\u7528\u800c\u4e0d\u81ea\u77e5\u7684\u64cd\u4f5c\u3002\u5b57\u6bcd\u03a0\u7684\u542b\u4e49\u662f\u300c\u6295\u5f71\u300d(Projection)\uff0c\u5728\u300c\u5411\u91cf\u300d\u7684\u8bed\u5883\u4e0b\uff0c\u7701\u7565\u4e00\u4e9b\u5206\u91cf\uff0c\u4fdd\u7559\u4e00\u4e9b\u5206\u91cf\uff0c\u76f8\u5f53\u4e8e\u628a\u5411\u91cf\u300c\u6295\u5f71\u5230\u4f4e\u7ef4\u7a7a\u95f4\u300d\u3002\u5728\u8fd9\u91cc\u662f\u7c7b\u4f3c\u7684\uff0c\u7701\u7565\u4e00\u4e9b\u5217\u7684\u7ed3\u679c\uff0c\u4fdd\u7559\u4e00\u4e9b\u5217\u7684\u7ed3\u679c\uff0c\u5c31\u662f\u300c\u6295\u5f71\u300d\uff0c\u6216\u79f0\u300c\u9009\u62e9\u5217\u300d\u3002<\/p>\n\n\n\n

\u5982\u60f3\u4ece\u96c6\u5408instructor<\/code>\u4e2d\u53d6\u51fa\u59d3\u540dname<\/code>\u548c\u6027\u522bgender<\/code>\uff0c\u5199\u6210\u5173\u7cfb\u4ee3\u6570\u5c31\u662f\u03a0name,gender(instructor)\u3002\u4f60\u53ef\u80fd\u66f4\u52a0\u719f\u6089SQL\uff0c\u540c\u6837\u7684\u64cd\u4f5c\uff0c\u5199\u6210SQL\u5c31\u662fselect name gender from instructor;<\/code><\/p>\n\n\n\n

\u5173\u7cfb\u4ee3\u6570\u548cSQL\u8bed\u53e5\u4e00\u6837\uff0c\u53ef\u4ee5\u300c\u5d4c\u5957\u300d\uff0c\u5199\u6cd5\u975e\u5e38\u81ea\u7136\u3002\u4ece\u4e0a\u9762\u6761\u4ef6\u7b5b\u67e5\u51fa\u6765\u7684\u9ad8\u5de5\u8d44\u5927\u4f6c\u4e2d\u62ff\u5230\u4ed6\u4eec\u7684\u59d3\u540d\u548c\u6027\u522b\uff0c\u5199\u6210\u5173\u7cfb\u4ee3\u6570\u5c31\u662f\u03a0name,gender(\u03c3salary>2000(instructor))\uff0c\u975e\u5e38\u81ea\u7136\uff01<\/p>\n\n\n\n

\u540c\u7406\u53ef\u4ee5\u5199\u51fa\u5bf9\u5e94\u7684SQL\uff0cselect name gender from instructor where salary > 2000;<\/code>\u3002SQL\u7684\u5f62\u5f0f\u4e0d\u662f\u5d4c\u5957\u7684\uff0c\u4f46\u662f\u4f60\u53ef\u4ee5\u7406\u89e3\u4e3a\u4e24\u4e2a\u8fc7\u7a0b\u03c3,\u03a0\u5408\u5e76\u4e3a\u4e00\u4e2a\u8fc7\u7a0b\u03a0(\u03c3())\uff0c\u5206\u522b\u5bf9\u5e94where<\/code>\u548cname gender<\/code>\u5217\u8868\u3002<\/p>\n\n\n\n

\u7b1b\u5361\u5c14\u4e58\u79ef\u00d7 (Cartesian Product)<\/h2>\n\n\n\n

\u4e0a\u9762\u4e24\u4e2a\u8bb0\u53f7\u5b9a\u4e49\u4e86\u5f88\u5e38\u7528\u5f88\u7b80\u5355\u7684\u64cd\u4f5c\uff0c\u8fd9\u4e2a\u8bb0\u53f7\u53ef\u80fd\u6709\u4e00\u70b9\u70b9\u964c\u751f\u3002<\/p>\n\n\n\n

\u4f60\u4e00\u5b9a\u542c\u8bf4\u8fc7\u4e24\u4e2a\u8868\u7684\u300c\u8fde\u63a5\u300d\uff0c\u6709\u300c\u5185\u8fde\u63a5\u300d\u3001\u300c\u5916\u8fde\u63a5\u300d\u3001\u300c\u81ea\u8fde\u63a5\u300d\u7b49\u7b49\u7b49\u3002\u7b1b\u5361\u5c14\u4e58\u79ef\u662f\u5b9e\u73b0\u8fde\u63a5\u6700\u7b80\u5355\u7684\u65b9\u5f0f\uff0c\u9488\u5bf9\u4e0d\u540c\u7684\u8fde\u63a5\u65b9\u5f0f\u548c\u6570\u636e\u60c5\u51b5\uff0c\u53ef\u4ee5\u6709\u5404\u79cd\u5404\u6837\u7684\u4f18\u5316\u3002\u8fd9\u91cc\u4ece\u8fd9\u4e2a\u6700\u7b80\u5355\u7684\u5f00\u59cb\u3002<\/p>\n\n\n\n

\u628a\u4e24\u4e2a\u96c6\u5408\u505a\u7b1b\u5361\u5c14\u4e58\u79ef\uff0c\u5c31\u662f\u8ba9\u4e24\u4e2a\u96c6\u5408\u7684\u300c\u6bcf\u4e00\u884c\u300d\u7684\u300c\u6240\u6709\u7ec4\u5408\u300d\u7ec4\u6210\u4e00\u4e2a\u65b0\u7684\u96c6\u5408\u3002<\/p>\n\n\n\n

\"\"\/<\/div>
\u7b1b\u5361\u5c14\u4e58\u79ef\u548c\u7ed3\u679c\u96c6<\/figcaption><\/figure>\n\n\n\n

\u5982\u4e0a\u56fe\u6240\u793a\uff0c\u6700\u53f3\u8fb9\u7684\u8868\u662f\u5de6\u8fb9\u4e24\u4e2a\u8868\u7684\u4e58\u79ef\u3002\u88681\u7684\u6bcf\u4e00\u884c\u4e00\u5171\u53ef\u4ee5\u548c\u88682\u76843\u884c\u7ec4\u5408\uff0c\u88681\u4e00\u51713\u884c\uff0c\u6545\u6700\u7ec8\u4e00\u51713\u00d73=9\u884c\u3002<\/p>\n\n\n\n

\u82e5\u4e24\u4e2a\u8868\u505a\u7b1b\u5361\u5c14\u4e58\u79ef\uff0c\u7ed3\u679c\u96c6\u7684\u884c\u6570\u662f\u4e24\u4e2a\u8868\u884c\u6570\u7684\u4e58\u79ef\u3002<\/p>\n\n\n\n

\u8981\u8fde\u63a5\u4e24\u4e2a\u8868\u683c\uff0c\u53ea\u9700\u8981\u7b5b\u9009\u7ed3\u679c\u96c6\u5c31\u53ef\u4ee5\u4e86\u3002\u5982\u6709\u4e24\u4e2a\u8868\uff0c\u4e00\u4e2a\u8868\u793a\u6388\u8bfe\u6559\u5e08instructor<\/code>\uff0c\u4e00\u4e2a\u662f\u8bfe\u7a0b\u4fe1\u606fcourse<\/code>\uff0c\u4ed6\u4eec\u5206\u522b\u5305\u542bname<\/code>\u5c5e\u6027\u548cteacher<\/code>\u5c5e\u6027\uff0c\u90fd\u8868\u793a\u300c\u6559\u5e08\u59d3\u540d\u300d\u3002\u5c06\u4e24\u4e2a\u8868\u505a\u7b1b\u5361\u5c14\u4e58\u79ef\uff0c\u7ed3\u679c\u96c6\u4e2d\u4fdd\u7559\u6559\u5e08\u59d3\u540d\u76f8\u540c\u7684\u884c\u5c31\u662f\u6211\u4eec\u60f3\u8981\u7684\u7ed3\u679c\u3002\u5199\u6210\u5173\u7cfb\u4ee3\u6570\u03c3instructor.name=course.teacher(instructor\u00d7course)\uff0c\u5199\u6210SQL\u8bed\u53e5select * from instructor, course where instructor.name = course.teacher;<\/code>\u3002<\/p>\n\n\n\n

\u6211\u4eec\u5f97\u5230\u4e86\u91cd\u8981\u7684\u7ed3\u8bba\uff1a\u8fde\u63a5=\u7b5b\u9009+\u7b1b\u5361\u5c14\u4e58\u79ef<\/em>\u3002<\/p>\n\n\n\n

\u8fde\u63a5<\/h2>\n\n\n\n

\u8fde\u63a5\u6709\u4e13\u95e8\u7684\u8bb0\u53f7\u22c8\uff0c\u4e0b\u6807\u8868\u793a\u8fde\u63a5\u7684\u6761\u4ef6\u3002\u5982\u4e0a\u9762\u7684\u8fde\u63a5\u64cd\u4f5c\u53ef\u4ee5\u5199\u6210\u22c8instructor.name=course.teacher(instructor,course)\u3002<\/p>\n\n\n\n

\u66f4\u591a\u7684\u4e5f\u5c31\u4e0d\u591a\u8bf4\uff0c\u540e\u6587\u4e13\u95e8\u8bb2\u89e3\u8fde\u63a5\u7684\u5404\u79cd\u60c5\u51b5\u3002<\/p>\n\n\n\n

\u5176\u4ed6<\/h2>\n\n\n\n

\u5269\u4f59\u7684\u5173\u7cfb\u4ee3\u6570\u8bb0\u53f7\u975e\u5e38\u7b80\u5355\uff0c\u4e0d\u9700\u8981\u592a\u591a\u89e3\u91ca\u3002<\/p>\n\n\n\n

\u03c1\u662f\u300c\u91cd\u547d\u540d\u300d\uff0cSQL\u8bed\u53e5\u4e2d\u5bf9\u5e94as<\/code>\u5173\u952e\u5b57\uff0c\u4e2a\u4eba\u611f\u89c9\u6ca1\u5fc5\u8981\u4e13\u95e8\u62ff\u4e00\u4e2a\u5b57\u6bcd\u8868\u8fbe\u8fd9\u4e48\u7b80\u5355\u7684\u64cd\u4f5c\u3002<\/p>\n\n\n\n

\u96c6\u5408\u64cd\u4f5c\u6709\u300c\u4ea4\u96c6\u300d\u300c\u5e76\u96c6\u300d\u300c\u8865\u96c6\u300d\u300c\u5dee\u96c6\u300d\uff0c\u662f\u9ad8\u4e2d\u6570\u5b66\u7684\u7b80\u5355\u5e38\u8bc6\uff0c\u4e5f\u5c31\u4e0d\u8d39\u7bc7\u5e45\u4e86\u3002<\/p>\n\n\n\n

\u8fde\u63a5 (Join)<\/h2>\n\n\n\n

\u6211\u4eec\u77e5\u9053\uff0c\u8fde\u63a5\u53ef\u4ee5\u7406\u89e3\u4e3a\u7b5b\u9009+\u7b1b\u5361\u5c14\u4e58\u79ef<\/code>\uff0c\u5373\u4fbf\u771f\u5b9e\u7684\u7b97\u6cd5\u53ef\u4ee5\u505a\u5f88\u591a\u4f18\u5316\uff0c\u57fa\u672c\u601d\u60f3\u4e0d\u4f1a\u53d8\u3002\u7b1b\u5361\u5c14\u4e58\u79ef\u662f\u56fa\u5b9a\u7684\uff0c\u8ba9\u8fde\u63a5\u64cd\u4f5c\u53d8\u5f97\u590d\u6742\u7684\uff0c\u53ea\u6709\u7b5b\u9009<\/code>\u64cd\u4f5c\uff0c\u4e5f\u5c31\u662f\u7b5b\u9009\u6761\u4ef6<\/code>\u3002\u6839\u636e\u4e0d\u540c\u7684\u7b5b\u9009\u6761\u4ef6\uff0cSQL\u63d0\u4f9b\u4e86\u4e0d\u540c\u7684\u4e66\u5199\u65b9\u5f0f\uff0c\u5e2e\u52a9\u7a0b\u5e8f\u5458\u660e\u786e\u76ee\u7684\u3001\u51cf\u5c11\u610f\u6599\u4e4b\u5916\u7684\u4e8b\u60c5\uff0c\u4e5f\u589e\u52a0\u4e86\u5b66\u4e60\u7684\u96be\u5ea6\u3002\u53ea\u8981\u7262\u8bb0\uff0c\u5404\u79cd\u8fde\u63a5\u5c31\u662f\u7b5b\u9009\u6761\u4ef6\u4e0d\u540c<\/em>\uff0c\u4e5f\u5c31\u53ef\u4ee5\u5f88\u5bb9\u6613\u5730\u533a\u5206\u5404\u79cd\u8fde\u63a5\u4e86\u3002<\/p>\n\n\n\n

\u4ee5\u4e0b\u6328\u4e2a\u4ecb\u7ecd\u5e38\u7528\u7684\u8fde\u63a5\u65b9\u5f0f\uff0c\u540c\u65f6\u5448\u73b0\u5bf9\u5e94SQL\u7684\u5199\u6cd5\u3002<\/p>\n\n\n\n

\u81ea\u7136\u8fde\u63a5 (Natural Join)<\/h2>\n\n\n\n

\u4e24\u4e2a\u8868\u4e2d\u542b\u6709\u76f8\u540c\u7684\u300c\u5c5e\u6027\u300d\uff0c\u6216\u79f0\u300c\u5217\u300d\uff0c\u5728\u7b1b\u5361\u5c14\u4e58\u79ef\u7684\u7ed3\u679c\u96c6\u4e2d\uff0c\u7b5b\u9009\u8fd9\u4e9b\u76f8\u540c\u5c5e\u6027\u76f8\u7b49\u7684\u60c5\u51b5\u3002<\/p>\n\n\n\n

\u524d\u6587\u8bb2\u89e3\u7b1b\u5361\u5c14\u96c6\u5408\u65f6\u7684\u4f8b\u5b50\u5c31\u662f\u4e00\u79cd\u81ea\u7136\u8fde\u63a5\uff0c\u76f8\u540c\u7684\u5217\u662f\u8868\u8fbe\u6559\u5e08\u59d3\u540d\u7684\u4e24\u4e2a\u5c5e\u6027\u3002\u4f46\u662f\uff0c \u4eceSQL\u7684\u89d2\u5ea6\u8bf4\uff0c\u8fd9\u4e2a\u4f8b\u5b50\u5e76\u4e0d\u81ea\u52a8\u6784\u6210\u300c\u81ea\u7136\u8fde\u63a5\u300d\uff0c\u56e0\u4e3a\u4e24\u4e2a\u5217\u7684\u300c\u540d\u79f0\u300d\u4e0d\u540c\u3002\u628ainstructor<\/code>\u8868\u4e2d\u7684\u5217\u540d\u6539\u4e3ateacher<\/code>\uff0c\u6216\u628acourse<\/code>\u8868\u4e2d\u7684\u5217\u540d\u6539\u4e3aname<\/code>\uff0c\u624d\u53ef\u4ee5\u81ea\u52a8\u6784\u6210SQL\u610f\u4e49\u4e0b\u7684\u300c\u81ea\u8fde\u63a5\u300d\u3002<\/p>\n\n\n\n

\u867d\u7136SQL\u6709\u6240\u89c4\u5b9a\uff0c\u4f46\u662f\u6211\u4eec\u77e5\u9053\uff0c\u81ea\u7136\u8fde\u63a5\u5b9e\u9645\u5212\u51fa\u4e86\u4e00\u7c7b\u8fde\u63a5\uff0c\u4ee3\u8868\u300c\u4f7f\u7528\u76f8\u7b49\u6761\u4ef6\u7b5b\u9009\u300d\u3002\u53ea\u8981\u6211\u4eec\u660e\u786e\uff0c\u300c\u4f7f\u7528\u76f8\u7b49\u6761\u4ef6\u7b5b\u9009\u300d\u662f\u6709\u76f4\u63a5SQL\u652f\u6301\u7684\uff0c\u5c31\u53ef\u4ee5\u4e86\u3002<\/p>\n\n\n\n

\u8bf4\u4e86\u8fd9\u4e48\u591a\uff0c\u8fd8\u6ca1\u8bf4SQL\u600e\u4e48\u5199\u3002<\/p>\n\n\n\n

\u6700\u7b80\u5355\u7684\u662f\u76f4\u63a5\u4f7f\u7528SQL\u63d0\u4f9b\u7684\u5173\u952e\u5b57natural join<\/code>\u3002\u5047\u8bbestudent<\/code>\u8868\u548ctakes<\/code>\u8868\u6709\u76f8\u540c\u7684\u5217ID<\/code>\uff0c\u5219\u4ee5\u4e0b\u4e24\u884cSQL\u7b49\u4ef7\uff1a<\/p>\n\n\n\n

select name, title from student natural join takes;\nselect name, title from student, takes where student.ID = takes.ID;<\/code><\/pre>\n\n\n\n
\u5173\u952e\u5b57natural join<\/code>\u76f8\u5f53\u4e8e\u81ea\u52a8\u6dfb\u52a0\u4e86where<\/code>\u8bed\u53e5\uff0c\u81ea\u52a8\u68c0\u67e5\u4e86\u4e24\u4e2a\u8868\u7684\u54ea\u51e0\u4e2a\u5c5e\u6027\u76f8\u540c\u3002<\/p>\n\n\n\n
\u4e5f\u53ef\u4ee5\u540c\u65f6\u64cd\u4f5c\u591a\u4e2a\u8868\uff0c\u591a\u5199\u51e0\u4e2anatural join<\/code>\u5c31\u53ef\u4ee5\u4e86\u3002\u5f53\u7136\uff0c\u524d\u63d0\u662f\u591a\u4e2a\u8868\u90fd\u5b58\u5728\u540c\u6837\u7684\u5217\u3002<\/p>\n\n\n\n
select name, title \nfrom student natural join takes natural join course;<\/code><\/pre>\n\n\n\n
\u65e0\u8bba\u6709\u591a\u5c11\u4e2a\u8868\u88ab\u540c\u65f6\u64cd\u4f5c\uff0cSQL\u89e3\u91ca\u5668\u90fd\u4f1a\u627e\u5230\u8fd9\u4e9b\u8868\u5171\u6709\u7684\u76f8\u540c\u5217\uff0c\u4ee5\u8fd9\u4e9b\u5217\u7684\u76f8\u7b49\u4e3a\u6761\u4ef6\uff0c\u7b5b\u9009\u4ea7\u751f\u7ed3\u679c\u96c6\u3002<\/p>\n\n\n\n
\u6307\u5b9a\u8fde\u63a5\u6761\u4ef6<\/h2>\n\n\n\n
\u8fd9\u6837\u81ea\u52a8\u627e\u76f8\u540c\u5217\u7684\u64cd\u4f5c\u5341\u5206\u65b9\u4fbf\uff0c\u540c\u65f6\u4e5f\u5341\u5206\u5371\u9669\u3002\u8981\u662f\u7a0b\u5e8f\u5458\u7c97\u5fc3\u5730\u770b\u6f0f\u4e86\u4e00\u4e9b\u5217\u540d\uff0c\u6216\u662f\u5bf9\u8868\u7ed3\u6784\u6709\u4e0d\u6b63\u786e\u7684\u9884\u671f\uff0c\u53ef\u80fd\u5bfc\u81f4\u6570\u636e\u5e93\u91c7\u7528\u7684\u76f8\u7b49\u6761\u4ef6\u6bd4\u7a0b\u5e8f\u5458\u8bbe\u60f3\u7684\u8981\u591a\u3002SQL\u4e5f\u63d0\u4f9b\u4e86\u624b\u52a8\u6307\u5b9a\u8fde\u63a5\u5c5e\u6027\u7684\u65b9\u6cd5\u3002<\/p>\n\n\n\n
\u5982\u8981\u8fde\u63a5\u8868\u793a\u9009\u8bfe\u60c5\u51b5\u7684\u8868takes<\/code>\u548c\u8bfe\u7a0b\u5217\u8868course<\/code>\uff0c\u6307\u5b9a\u4ee5\u5c5e\u6027course_id<\/code>\u76f8\u7b49\u4e3a\u7b5b\u9009\u6761\u4ef6\u3002\u4ee5\u4e0bSQL\u8bed\u53e5\u7b49\u4ef7\uff1a<\/p>\n\n\n\n
select name, title from takes join course using(course_id);\nselect name, title from takes, course where takes.course_id = course.course_id;<\/code><\/pre>\n\n\n\n
\u4e5f\u53ef\u4ee5\u6307\u5b9a\u591a\u4e2a\u5c5e\u6027\uff0c\u76f8\u5f53\u4e8e\u591a\u4e2a\u7b5b\u9009\u6761\u4ef6\uff1a<\/p>\n\n\n\n
select name, title from takes join course using(course_id, course_name);<\/code><\/pre>\n\n\n\n
join...using...<\/code>\u5f62\u5f0f\u7684\u8bed\u53e5\u53ef\u4ee5\u5f88\u65b9\u4fbf\u5730\u6307\u5b9a\u300c\u76f8\u7b49\u300d\u6761\u4ef6\uff0cSQL\u540c\u6837\u63d0\u4f9b\u4e86\u6307\u5b9a\u5176\u4ed6\u6761\u4ef6\u7684\u65b9\u5f0f\uff0c\u4e5f\u5c31\u662fjoin...on...<\/code>\u3002on<\/code>\u8bed\u53e5\u540c\u6837\u53ef\u4ee5\u6307\u5b9a\u76f8\u7b49\u6761\u4ef6\uff0c\u5982\u4e0a\u9762\u7684SQL\u7b49\u4ef7\u4e8e\u4ee5\u4e0bSQL\uff1a<\/p>\n\n\n\n
select name, title from takes join course on takes.course_id = course.course_id;<\/code><\/pre>\n\n\n\n
on<\/code>\u5173\u952e\u5b57\u53ef\u4ee5\u6307\u5b9a\u4efb\u610f\u7b5b\u9009\u6761\u4ef6\uff0c\u8fd9\u5c31\u53ef\u4ee5\u5b9e\u73b0\u4efb\u610f\u5f62\u5f0f\u7684\u8fde\u63a5\uff0c\u4e5f\u589e\u52a0\u4e86\u6211\u4eec\u5b66\u4e60\u7684\u96be\u5ea6\u3002<\/p>\n\n\n\n
\u4f60\u53ef\u80fd\u8ba4\u4e3a\uff0cwhere<\/code>\u5173\u952e\u5b57\u53ef\u4ee5\u76f4\u63a5\u7b5b\u9009\u7b1b\u5361\u5c14\u4e58\u79ef\u7684\u7ed3\u679c\uff0c\u6ca1\u6709\u5fc5\u8981\u4f7f\u7528on<\/code>\u6216using<\/code>\u3002\u8fd9\u662f\u4e2a\u4eba\u4e60\u60ef\u95ee\u9898\uff0c\u89c1\u4ec1\u89c1\u667a\u3002\u7136\u800c\uff0cwhere<\/code>\u901a\u5e38\u7528\u4f5c\u5bf9\u7ed3\u679c\u96c6\u6700\u540e\u7684\u7b5b\u9009\uff0c\u800con using<\/code>\u4e13\u95e8\u7528\u4f5c\u8fde\u63a5\u65f6\u5019\u7684\u7b5b\u9009\uff0c\u9075\u5b88\u4e00\u4e9b\u89c4\u5b9a\uff0c\u4e0d\u4f46\u53ef\u4ee5\u5e2e\u52a9SQL\u89e3\u91ca\u5668\u51cf\u8f7b\u8d1f\u62c5\uff0c\u8fd8\u53ef\u4ee5\u8ba9\u81ea\u5df1\u7684\u5de5\u4f5c\u66f4\u52a0\u6e05\u6670\u660e\u4e86\u3002<\/p>\n\n\n\n
\u5916\u8fde\u63a5 (Outer Join)<\/h2>\n\n\n\n
\u4f7f\u7528\u300c\u81ea\u7136\u8fde\u63a5\u300d\u65f6\uff0c\u82e5\u6709\u4e00\u4e2a\u53d6\u503c\u6ca1\u6709\u540c\u65f6\u51fa\u73b0\u5728\u4e24\u4e2a\u8868\u4e2d\uff0c\u8fde\u63a5\u7684\u7ed3\u679c\u96c6\u4e2d\u4e5f\u4e0d\u4f1a\u51fa\u73b0\u8fd9\u4e2a\u53d6\u503c\u3002\u82e5\u6709\u4e2a\u5b66\u751f\u6ca1\u6709\u9009\u4efb\u4f55\u8bfe\u7a0b\uff0c\u5728\u5b66\u751f\u8868student<\/code>\u4e2d\u6709\u4ed6\uff0c\u4f46\u662f\u5728\u9009\u8bfe\u8868takes<\/code>\u4e2d\u6ca1\u6709\u4ed6\uff0c\u90a3\u4e48\u4ee5\u300c\u5b66\u751f\u59d3\u540d\u76f8\u7b49\u300d\u4f5c\u4e3a\u8fde\u63a5\u7b5b\u9009\u6761\u4ef6\u7684\u7ed3\u679c\u96c6\u4e2d\u4e5f\u4e0d\u4f1a\u51fa\u73b0\u8fd9\u4e2a\u5b66\u751f\u7684\u540d\u5b57\u3002<\/p>\n\n\n\n
\u5728\u5927\u591a\u6570\u60c5\u51b5\u4e0b\uff0c\u6211\u4eec\u60f3\u8981\u8fd9\u6837\u7684\u6548\u679c\u3002\u4f46\u662f\uff0c\u6211\u4eec\u6709\u65f6\u4e5f\u60f3\u4fdd\u7559\u5176\u4e2d\u4e00\u4e2a\u8868\u7684\u4fe1\u606f\uff0c\u4e0d\u5e0c\u671b\u8fde\u63a5\u4e4b\u540e\u5f97\u5230\u7684\u8868\u4fe1\u606f\u7f3a\u5931\u3002\u8fd9\u5c31\u662f\u300c\u5916\u8fde\u63a5\u300d\u3002<\/p>\n\n\n\n
\u5f53\u6307\u5b9a\u8fde\u63a5\u65b9\u5f0f\u4e3a\u300c\u5916\u8fde\u63a5\u300d\u65f6\uff0c\u5373\u4fbf\u6709\u7684\u5143\u7d20\u6ca1\u6709\u540c\u65f6\u51fa\u73b0\u5728\u4e24\u5f20\u8868\u91cc\uff0c\u4e5f\u4f1a\u88ab\u4fdd\u7559\u3002\u5982\u4e00\u4e2a\u6ca1\u6709\u9009\u4efb\u4f55\u8bfe\u7684\u5b66\u751f\uff0c\u6307\u5b9a\u5916\u8fde\u63a5\u540e\uff0c\u8fd9\u4e2a\u5b66\u751f\u5728\u5b66\u751f\u8868student<\/code>\u4e2d\u7684\u4fe1\u606f\u4f1a\u5b8c\u6574\u51fa\u73b0\u5728\u7ed3\u679c\u96c6\u4e2d\uff0c\u800c\u76f8\u5e94\u884c\u4e2d\u6765\u81ea\u9009\u8bfe\u8868takes<\/code>\u7684\u4fe1\u606f\u5219\u4e0d\u4f1a\u51fa\u73b0\uff0c\u4ee5\u300c\u7a7a\u300d\u663e\u793a\u3002\u53ef\u80fd\u5f62\u5f0f\u5982\u4e0b\uff1a<\/p>\n\n\n\n
\"\"\/<\/div>
\u5916\u8fde\u63a5<\/figcaption><\/figure>\n\n\n\n
SQL\u8bed\u53e5\u4e2d\u5bf9\u5e94\u7684\u5173\u952e\u5b57\u662fouter join<\/code>\uff0c\u53ef\u4ee5\u52a0\u4e0a\u524d\u7f00left<\/code>\u6216right<\/code>\u6216full<\/code>\uff0c\u8868\u793a\u300c\u5de6\u8fde\u63a5\u300d\u3001\u300c\u53f3\u8fde\u63a5\u300d\u548c\u300c\u5168\u8fde\u63a5\u300d\u3002\u6240\u8c13\u300c\u5de6\u53f3\u300d\u7684\u610f\u601d\u662f\uff0c\u4fdd\u7559outer join<\/code>\u64cd\u4f5c\u7b26\u5de6\u8fb9\u6216\u662f\u53f3\u8fb9\u7684\u5217\u7684\u4fe1\u606f\u3002\u5982\u4e0a\u56fe\u7684\u7ed3\u679c\u96c6\uff0c\u5c31\u662f\u4e00\u4e2a\u300c\u5de6\u8fde\u63a5\u300d\u7684\u7ed3\u679c\u96c6\uff0c\u4fdd\u7559\u4e86\u5de6\u8fb9student<\/code>\u8868\u7684\u4fe1\u606f\uff0c\u800c\u6ca1\u6709\u4fdd\u7559\u53f3\u8fb9takes<\/code>\u8868\u7684\u4fe1\u606f\uff0c\u51fa\u73b0\u5728takes<\/code>\u8868\u4e2d\u7684\u4fe1\u606f\u8981\u662f\u6ca1\u6709\u51fa\u73b0\u5728student<\/code>\u8868\u4e2d\uff0c\u4e5f\u5c31\u4e0d\u4f1a\u51fa\u73b0\u5728\u7ed3\u679c\u96c6\u4e2d\u3002<\/p>\n\n\n\n
full<\/code>\u4ee3\u8868\u8981\u540c\u65f6\u4fdd\u7559\u4e24\u4e2a\u8868\u7684\u4fe1\u606f\uff0c\u5982\u679c\u4e00\u4e2a\u8868\u4e2d\u7684\u4fe1\u606f\u5728\u53e6\u4e00\u4e2a\u8868\u4e2d\u6ca1\u51fa\u73b0\uff0c\u5c31\u628a\u6ca1\u51fa\u73b0\u7684\u4fe1\u606f\u663e\u793a\u4e3a\u300c\u7a7a\u300d\uff0c\u9053\u7406\u662f\u76f8\u540c\u7684\u3002<\/p>\n\n\n\n
\u4e0a\u56fe\u5bf9\u5e94SQL\u8bed\u53e5\u5982\u4e0b\uff0c\u540c\u6837\u4f7f\u7528on<\/code>\u6765\u6307\u5b9a\u8fde\u63a5\u6761\u4ef6\u3002<\/p>\n\n\n\n
select * from student left outer join takes on student.name = takes.name;<\/code><\/pre>\n\n\n\n
\u76f8\u540c\u7684\u7ed3\u679c\u53ef\u4ee5\u7531\u300c\u987a\u5e8f\u76f8\u53cd\u300d\u7684\u53f3\u8fde\u63a5\u5f97\u5230\uff1a<\/p>\n\n\n\n
select * from takes right outer join student on student.name = takes.name;<\/code><\/pre>\n\n\n\n
\u4e0a\u9762\u4e24\u4e2aSQL\u5f97\u5230\u7684\u7ed3\u679c\u96c6\u76f8\u540c\u3002\u8fd9\u63d0\u9192\u6211\u4eec\uff0c\u65e0\u8bba\u662f\u5de6\u8fde\u63a5\u8fd8\u662f\u53f3\u8fde\u63a5\uff0c\u751a\u81f3\u662f\u5168\u8fde\u63a5\uff0c\u91cd\u8981\u7684\u662f\u6307\u5b9a\u597d\u300c\u8981\u4fdd\u7559\u54ea\u4e2a\u8868\u7684\u4fe1\u606f\u300d\uff0c\u800c\u4e0d\u662f\u300c\u8fde\u63a5\u7684\u540d\u5b57\u662f\u4ec0\u4e48\u300d\u3002<\/p>\n\n\n\n
\u4ece\u5185\u8fde\u63a5\u5230\u5916\u8fde\u63a5<\/h2>\n\n\n\n
\u300c\u5185\u8fde\u63a5\u300d\u662f\u548c\u300c\u5916\u8fde\u63a5\u300d\u76f8\u5bf9\u7684\u6982\u5ff5\uff0c\u4e5f\u5c31\u662f\u4e22\u5f03\u6ca1\u6709\u540c\u65f6\u51fa\u73b0\u5728\u4e24\u4e2a\u8868\u4e2d\u7684\u6570\u636e\uff0c\u4e5f\u5c31\u662f\u6211\u4eec\u4e00\u5f00\u59cb\u4ecb\u7ecd\u7684\u8fde\u63a5\u65b9\u5f0f\u3002\u53ef\u4ee5\u901a\u8fc7\u5185\u8fde\u63a5\u7406\u89e3\u5916\u8fde\u63a5\u3002<\/p>\n\n\n\n
\u4e24\u4e2a\u8868\u8fdb\u884c\u5185\u8fde\u63a5\u540e\uff0c\u6709\u7684\u884c\u6ee1\u8db3\u5185\u8fde\u63a5\u7684\u7b5b\u9009\u6761\u4ef6\uff0c\u6709\u7684\u4e0d\u6ee1\u8db3\u3002\u7ed9\u4e0d\u6ee1\u8db3\u7b5b\u9009\u6761\u4ef6\u7684\uff0c\u76f8\u5e94\u586b\u8865\u7a7a\u503c\uff0c\u5f97\u5230\u7684\u5c31\u662f\u300c\u5916\u8fde\u63a5\u300d\u7684\u7ed3\u679c\u96c6\u3002<\/p>\n\n\n\n
\u7531\u6b64\uff0c\u6211\u4eec\u53ef\u4ee5\u8fd9\u6837\u7406\u89e3\uff1a\u5916\u8fde\u63a5=\u5185\u8fde\u63a5+Null\u586b\u8865<\/em>\u3002<\/p>\n\n\n\n
\u5916\u8fde\u63a5\u6761\u4ef6\u4f7f\u7528where<\/code><\/h2>\n\n\n\n
\u5916\u8fde\u63a5\u7684\u7b5b\u9009\u6761\u4ef6\u4e0d\u80fd\u7528where<\/code>\u5199\u3002<\/p>\n\n\n\n
\u8003\u8651\u8fd9\u6837\u4e00\u4e2aSQL\u8bed\u53e5\uff1a<\/p>\n\n\n\n
select * from student left outer join takes on true where student.ID = takes.ID;<\/code><\/pre>\n\n\n\n
\u8fd9\u4e2aSQL\u8bed\u53e5\uff0c\u8fde\u63a5\u7684\u7ed3\u679c\u96c6\u662f\u5b8c\u6574\u7684\u3001\u6ca1\u6709\u7b5b\u9009\u8fc7\u7684\u7b1b\u5361\u5c14\u4e58\u79ef\u3002\u628a\u8fde\u63a5\u7684\u7ed3\u679c\u96c6\u901a\u8fc7where<\/code>\u7b5b\u9009\uff0c\u6700\u7ec8\u7ed3\u679c\u96c6\u4e2d\u4e00\u5b9a\u4e0d\u5b58\u5728ID<\/code>\u4e0d\u76f8\u7b49\u7684\u884c\uff0c\u8fd9\u4e0d\u662f\u6211\u4eec\u60f3\u8981\u7684\u300c\u5916\u8fde\u63a5\u300d\u7ed3\u679c\u3002<\/p>\n\n\n\n
\u4f60\u53ef\u4ee5\u505c\u4e0b\u6765\u60f3\u4e00\u60f3\uff0c\u6709\u6ca1\u6709\u53ef\u80fd\u901a\u8fc7where<\/code>\u5b9e\u73b0\u5916\u8fde\u63a5\u3002\u5f53\u7136\u662f\u4e0d\u53ef\u80fd\u7684\uff01\u56e0\u4e3a\u300c\u7b5b\u9009\u300d\u4e0d\u662f\u5916\u8fde\u63a5\u7684\u6700\u7ec8\u7ed3\u679c\uff0c\u8fd8\u6709\u586b\u8865\u7a7a\u503c\u8fd9\u4e00\u6b65\uff0c\u5e76\u4e14\u586b\u8865\u7a7a\u503c\u4f9d\u8d56\u7b5b\u9009\u7684\u7ed3\u679c\u3002<\/p>\n\n\n\n
\u4ea4\u53c9\u8fde\u63a5<\/h2>\n\n\n\n
\u4ea4\u53c9\u8fde\u63a5\u5c31\u662f\u76f4\u63a5\u4fdd\u7559\u7b1b\u5361\u5c14\u4e58\u79ef\u7684\u7ed3\u679c\u96c6\uff0c\u4e0d\u505a\u4efb\u4f55\u5904\u7406\uff0c\u6ca1\u6709\u592a\u591a\u597d\u8bf4\u7684\u3002\u666e\u901a\u7684\u9017\u53f7\u53ef\u4ee5\u89e6\u53d1\u4ea4\u53c9\u8fde\u63a5\uff0c\u5982select * from student, takes;<\/code>\u3002\u4e5f\u53ef\u4ee5\u4f7f\u7528cross join<\/code>\u5173\u952e\u5b57\uff0c\u5982select * from student cross join takes;<\/code>\u3002<\/p>\n\n\n\n
\u5e94\u8be5\u4e0d\u9700\u8981\u518d\u591a\u89e3\u91ca\u4e86\u3002<\/p>\n\n\n\n
\u81ea\u8fde\u63a5<\/h2>\n\n\n\n
\u540c\u4e00\u4e2a\u8868\u53ef\u4ee5\u5f53\u505a\u4e24\u4e2a\u8868\u6765\u4f7f\u7528\uff0c\u51fa\u73b0\u5728join<\/code>\u64cd\u4f5c\u7b26\u7684\u4e24\u8fb9\uff0c\u76f8\u540c\u7684\u8fde\u63a5\u64cd\u4f5c\u4ecd\u7136\u9002\u7528\u3002\u5982\u5217\u51fa\u6240\u6709\u7684\u5de5\u8d44\u5927\u5c0f\u5173\u7cfb\uff0c\u663e\u793a\u6240\u6709\u300c\u540c\u4e8bA\u6bd4\u540c\u4e8bB\u5de5\u8d44\u9ad8\u300d\u7684\u60c5\u51b5\u3002<\/p>\n\n\n\n
select higher.name as better_employee, lower.name as lower_employee\nfrom salary as higher join salary as lower\non higher.sal > lower.sal;<\/code><\/pre>\n\n\n\n
\u6839\u636e\u663e\u793a\u51fa\u6765\u7684\u300c\u5de5\u8d44\u6bd4\u8f83\u300d\uff0c\u4f60\u5c31\u53ef\u4ee5\u53bb\u6253\u6b7b\u6bd4\u4f60\u5de5\u8d44\u9ad8\u7684\u540c\u4e8b\u4e86\u3002<\/p>\n\n\n\n
\u5149\u662f\u53ef\u4ee5\u7528\u6765\u6253\u6b7b\u540c\u4e8b\u8fd8\u4e0d\u592a\u591f\uff0c\u300c\u81ea\u8fde\u63a5\u300d\u7684\u64cd\u4f5c\u573a\u666f\u66f4\u591a\u662f\u4e00\u79cd\u6811\u5f62\u7ed3\u6784\u7684\u5e8f\u5217\u5316\u65b9\u5f0f\uff0c\u5e38\u7528\u6765\u5904\u7406\u300c\u4e0a\u4e0b\u7ea7\u5173\u7cfb\u300d\u3002\u5177\u6709\u4e0a\u4e0b\u7ea7\u5173\u7cfb\u7684\u8868\uff0c\u901a\u5e38\u6709\u4e00\u4e2a\u552f\u4e00\u8868\u793a\u81ea\u5df1\u7684id\uff0c\u8fd8\u6709\u4e00\u4e2a\u8868\u793a\u7236\u5bf9\u8c61\u7684id\u3002Linux\u7684\u8fdb\u7a0b\u7ba1\u7406\u5668\u5c31\u662f\u4e00\u4e2a\u5f88\u597d\u7684\u4f8b\u5b50\u3002\u4e0b\u8868\u662f\u5728MacOSX\u7ec8\u7aef\u4e2d\u8f93\u5165ps -ej<\/code>\u5f97\u5230\u7684\u90e8\u5206\u7ed3\u679c\uff1a<\/p>\n\n\n\n
\"\"\/<\/div>
Mac\u8fdb\u7a0b\u8868<\/figcaption><\/figure>\n\n\n\n
PID<\/code>\u662f\u300c\u8fdb\u7a0b\u63cf\u8ff0\u7b26\u300d\uff0cPPID<\/code>\u662f\u7236\u8fdb\u7a0b\u7684\u300c\u8fdb\u7a0b\u63cf\u8ff0\u7b26\u300d\u3002\u53ef\u4ee5\u770b\u5230\uff0c\u5927\u591a\u6570\u8fdb\u7a0b\u7684\u7236\u8fdb\u7a0b\u90fd\u662f1\u53f7\u8fdb\u7a0b\uff0c\u4e5f\u5c31\u662f\/sbin\/launchd<\/code>\uff0c\u4e5f\u5c31\u662fMac\u7cfb\u7edf\u7684\u7956\u5b97\u8fdb\u7a0b\u3002\u8fd9\u4e2a\u8fdb\u7a0b\u662f\u7cfb\u7edf\u542f\u52a8\u4e4b\u540e\u542f\u52a8\u7684\u7b2c\u4e00\u4e2a\u8fdb\u7a0b\uff0c\u5b83\u7684\u7236\u8fdb\u7a0b\u7684\u300c\u8fdb\u7a0b\u63cf\u8ff0\u7b26\u300d\u662f\u7279\u6b8a\u503c0\u3002Mac\u7684\u8fdb\u7a0b\u542f\u52a8\u6b21\u5e8f\u5927\u6982\u5982\u4e0b\u56fe\uff0c\u662f\u4e2a\u6811\u5f62\u7ed3\u6784\u3002<\/p>\n\n\n\n
\"\"\/<\/div>
mac boot<\/figcaption><\/figure>\n\n\n\n
\u50cfMac\u7684\u8fdb\u7a0b\u8868\u8fd9\u6837\u6709\u7740\u6811\u5f62\u7ed3\u6784\u7684\u8868\u5c31\u662f\u6709\u300c\u6811\u5f62\u7ed3\u6784\u300d\u7684\uff0c\u6709\u552f\u4e00\u786e\u5b9a\u81ea\u8eab\u7684id\uff0c\u4e5f\u6709\u300c\u7236\u5bf9\u8c61\u300d\u7684id\u3002\u5f53\u6211\u4eec\u770b\u5230\u67d0\u4e00\u884c\uff0c\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7PPID<\/code>\u627e\u5230\u8fd9\u4e00\u884c\u7684\u7236\u5bf9\u8c61\u3002\u6bcf\u4e2a\u5bf9\u8c61\u90fd\u6709\u4e00\u4e2a\u7236\u5bf9\u8c61\uff0c\u8fd9\u6837\u5c31\u6784\u6210\u4e86\u4e00\u4e2a\u6811\u5f62\u7ed3\u6784\uff0c\u6839\u5bf9\u8c61\u7684\u7236\u5bf9\u8c61\u7528\u4e00\u4e2a\u7279\u6b8a\u503c\u6765\u8868\u793a\u3002<\/p>\n\n\n\n
\u53ef\u4ee5\u663e\u793a\u51fa\u6bcf\u4e2a\u8fdb\u7a0b\u7684\u7236\u8fdb\u7a0b\u7684\u547d\u4ee4\u548c\u81ea\u5df1\u7684\u547d\u4ee4\uff0cSQL\u8bed\u53e5\u5982\u4e0b\uff1a<\/p>\n\n\n\n
select child.command, parent.command\nfrom process as child join process as parent\non child.ppid = parent.pid;<\/code><\/pre>\n\n\n\n
\u8fde\u63a5\u603b\u7ed3<\/h2>\n\n\n\n
\u8981\u5199\u5e26\u6709\u8fde\u63a5\u7684\u67e5\u8be2\uff0c \u9700\u8981\u60f3\u6e05\u695a\u8fd9\u4e24\u4ef6\u4e8b\u60c5\uff1a<\/p>\n\n\n\n
  1. \u7b5b\u9009\u6761\u4ef6\u662f\u4ec0\u4e48\uff1f<\/li>
  2. \u662f\u5426\u4fdd\u7559\u53ea\u5728\u4e00\u4e2a\u8868\u4e2d\u51fa\u73b0\u8fc7\u7684\u4fe1\u606f\uff1f<\/li><\/ol>\n\n\n\n
    \u5176\u4f59\u7684\uff0c\u4e5f\u5c31\u5f88\u7b80\u5355\u5566\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"
    \u672c\u6587\u601d\u7ef4\u5bfc\u56fe\uff1a \u5173\u7cfb\u4ee3\u6570 (Relational Algebra) \u5173\u7cfb\u4ee3\u6570\u662f\u6570\u636e\u5e93\u64cd\u4f5c\u7684\u6570\u5b66\u7b26\u53f7\u4f53\u7cfb\uff0c\u53ef\u4ee5\u7406 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[25],"tags":[57],"class_list":["post-822","post","type-post","status-publish","format-standard","hentry","category-25","tag-57"],"_links":{"self":[{"href":"https:\/\/qaqaq.top\/index.php?rest_route=\/wp\/v2\/posts\/822"}],"collection":[{"href":"https:\/\/qaqaq.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/qaqaq.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/qaqaq.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/qaqaq.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=822"}],"version-history":[{"count":1,"href":"https:\/\/qaqaq.top\/index.php?rest_route=\/wp\/v2\/posts\/822\/revisions"}],"predecessor-version":[{"id":823,"href":"https:\/\/qaqaq.top\/index.php?rest_route=\/wp\/v2\/posts\/822\/revisions\/823"}],"wp:attachment":[{"href":"https:\/\/qaqaq.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=822"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/qaqaq.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=822"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/qaqaq.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=822"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}