{"id":455,"date":"2024-12-22T13:50:20","date_gmt":"2024-12-22T05:50:20","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=455"},"modified":"2024-12-22T13:50:20","modified_gmt":"2024-12-22T05:50:20","slug":"sql-%e9%87%8c%e6%80%8e%e4%b9%88%e5%ae%9e%e7%8e%b0%e6%9f%a5%e8%af%a2%e7%bb%93%e6%9e%9c%e5%8e%bb%e9%87%8d","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2024\/12\/22\/sql-%e9%87%8c%e6%80%8e%e4%b9%88%e5%ae%9e%e7%8e%b0%e6%9f%a5%e8%af%a2%e7%bb%93%e6%9e%9c%e5%8e%bb%e9%87%8d\/","title":{"rendered":"SQL\u00a0\u91cc\u600e\u4e48\u5b9e\u73b0\u67e5\u8be2\u7ed3\u679c\u53bb\u91cd"},"content":{"rendered":"\n
\n

\u5728 SQL \u67e5\u8be2\u4e2d\uff0c\u53bb\u91cd\u64cd\u4f5c\u4e3b\u8981\u901a\u8fc7 DISTINCT<\/code> \u5173\u952e\u5b57\u6765\u5b9e\u73b0\uff0cDISTINCT<\/code> \u7528\u4e8e\u79fb\u9664\u67e5\u8be2\u7ed3\u679c\u4e2d\u7684\u91cd\u590d\u8bb0\u5f55\uff0c\u53ea\u8fd4\u56de\u552f\u4e00\u7684\u8bb0\u5f55\u3002<\/p>\n<\/blockquote>\n\n\n\n

1. \u57fa\u672c\u8bed\u6cd5<\/strong><\/h3>\n\n\n\n
SELECT DISTINCT column1, column2, ... FROM table_name;<\/code><\/pre>\n\n\n\n
    \n
  • DISTINCT<\/code> \u540e\u9762\u53ef\u4ee5\u8ddf\u591a\u4e2a\u5217\uff0c\u8868\u793a\u67e5\u8be2\u7ed3\u679c\u4e2d\u4f1a\u53bb\u6389\u90a3\u4e9b\u5728\u6240\u6709\u5217\u7684\u7ec4\u5408\u4e0a\u5b8c\u5168\u76f8\u540c\u7684\u8bb0\u5f55\u3002<\/li>\n<\/ul>\n\n\n\n
    \n\n\n\n
    2. \u793a\u4f8b\uff1a<\/strong><\/h3>\n\n\n\n
    \u5047\u8bbe\u6709\u4e00\u4e2a employees<\/code> \u8868\uff0c\u5185\u5bb9\u5982\u4e0b\uff1a<\/p>\n\n\n\n
    id<\/th>name<\/th>department<\/th>salary<\/th><\/tr><\/thead>
    1<\/td>Alice<\/td>HR<\/td>5000<\/td><\/tr>
    2<\/td>Bob<\/td>IT<\/td>6000<\/td><\/tr>
    3<\/td>Alice<\/td>HR<\/td>5000<\/td><\/tr>
    4<\/td>Carol<\/td>HR<\/td>5500<\/td><\/tr>
    5<\/td>Alice<\/td>IT<\/td>7000<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    2.1 \u53bb\u91cd\u5355\u5217\uff1a<\/strong><\/h4>\n\n\n\n
    \u5982\u679c\u6211\u4eec\u53ea\u60f3\u53bb\u6389 name<\/code> \u5217\u4e2d\u7684\u91cd\u590d\u9879\uff0c\u53ef\u4ee5\u4f7f\u7528\uff1a<\/p>\n\n\n\n
    SELECT DISTINCT name FROM employees;<\/code><\/pre>\n\n\n\n
    \u7ed3\u679c\uff1a<\/strong><\/p>\n\n\n\n
    name<\/th><\/tr><\/thead>
    Alice<\/td><\/tr>
    Bob<\/td><\/tr>
    Carol<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    2.2 \u53bb\u91cd\u591a\u5217\uff1a<\/strong><\/h4>\n\n\n\n
    \u5982\u679c\u6211\u4eec\u5e0c\u671b\u53bb\u6389 name<\/code> \u548c department<\/code> \u5217\u7684\u91cd\u590d\u9879\uff0c\u53ef\u4ee5\u4f7f\u7528\uff1a<\/p>\n\n\n\n
    SELECT DISTINCT name, department FROM employees;<\/code><\/pre>\n\n\n\n
    \u7ed3\u679c\uff1a<\/strong><\/p>\n\n\n\n
    name<\/th>department<\/th><\/tr><\/thead>
    Alice<\/td>HR<\/td><\/tr>
    Bob<\/td>IT<\/td><\/tr>
    Carol<\/td>HR<\/td><\/tr>
    Alice<\/td>IT<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0cDISTINCT<\/code> \u4f1a\u786e\u4fdd\u6bcf\u4e00\u5bf9 (name, department)<\/code> \u7ec4\u5408\u662f\u552f\u4e00\u7684\uff0c\u6240\u4ee5 Alice<\/code> \u5728 HR<\/code> \u548c IT<\/code> \u90e8\u95e8\u7684\u8bb0\u5f55\u4f1a\u88ab\u4fdd\u7559\u3002<\/p>\n\n\n\n
    \n\n\n\n
    3. \u53bb\u91cd\u4e0e\u805a\u5408<\/strong><\/h3>\n\n\n\n
    \u6709\u65f6\uff0c\u4f60\u53ef\u80fd\u4e0d\u4ec5\u9700\u8981\u53bb\u91cd\uff0c\u8fd8\u60f3\u5bf9\u6570\u636e\u8fdb\u884c\u805a\u5408\u64cd\u4f5c\uff08\u4f8b\u5982\u8ba1\u7b97\u603b\u6570\u3001\u5e73\u5747\u503c\u7b49\uff09\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0cDISTINCT<\/code> \u53ef\u4ee5\u4e0e\u805a\u5408\u51fd\u6570\u4e00\u8d77\u4f7f\u7528\u3002<\/p>\n\n\n\n
    3.1 \u53bb\u91cd\u5e76\u8ba1\u7b97\u603b\u6570\uff1a<\/strong><\/h4>\n\n\n\n
    \u5982\u679c\u6211\u4eec\u8981\u7edf\u8ba1 name<\/code> \u5217\u4e2d\u4e0d\u540c\u5458\u5de5\u7684\u6570\u91cf\uff0c\u53ef\u4ee5\u8fd9\u6837\u505a\uff1a<\/p>\n\n\n\n
    SELECT COUNT(DISTINCT name) FROM employees;<\/code><\/pre>\n\n\n\n
    \u7ed3\u679c\uff1a<\/strong><\/p>\n\n\n\n
    COUNT(DISTINCT name)<\/th><\/tr><\/thead>
    3<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \u56e0\u4e3a Alice<\/code> \u5728\u8868\u4e2d\u6709\u591a\u6761\u8bb0\u5f55\uff0c\u4f46 DISTINCT<\/code> \u4f1a\u628a\u5b83\u4eec\u5408\u5e76\u4e3a\u4e00\u4e2a\u552f\u4e00\u8bb0\u5f55\u3002<\/p>\n\n\n\n
    3.2 \u53bb\u91cd\u5e76\u8ba1\u7b97\u5e73\u5747\u85aa\u8d44\uff1a<\/strong><\/h4>\n\n\n\n
    \u6211\u4eec\u8fd8\u53ef\u4ee5\u53bb\u91cd\u5e76\u8ba1\u7b97\u4e0d\u540c name<\/code> \u7684\u5e73\u5747\u85aa\u8d44\uff1a<\/p>\n\n\n\n
    SELECT AVG(DISTINCT salary) FROM employees;<\/code><\/pre>\n\n\n\n
    \u7ed3\u679c\uff1a<\/strong><\/p>\n\n\n\n
    AVG(DISTINCT salary)<\/th><\/tr><\/thead>
    6000<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \u5728\u6b64\u793a\u4f8b\u4e2d\uff0cDISTINCT<\/code> \u4f1a\u8ba1\u7b97\u85aa\u8d44\u4e2d\u7684\u552f\u4e00\u503c\uff085000\u30016000\u30015500\u30017000\uff09\uff0c\u7136\u540e\u6c42\u5176\u5e73\u5747\u503c\u3002<\/p>\n\n\n\n
    \n\n\n\n
    4. \u6ce8\u610f\u4e8b\u9879<\/strong><\/h3>\n\n\n\n
      \n
    • DISTINCT<\/code> \u53bb\u91cd\u7684\u662f\u5217\u7ec4\u5408<\/strong>\uff0c\u800c\u4e0d\u4ec5\u4ec5\u662f\u5355\u4e2a\u5217\u3002\u5982\u679c\u591a\u4e2a\u5217\u7ec4\u5408\u76f8\u540c\uff0cDISTINCT<\/code> \u4f1a\u53bb\u9664\u91cd\u590d\u7684\u884c\u3002<\/li>\n\n\n\n
    • \u6027\u80fd\u95ee\u9898<\/strong>\uff1a\u4f7f\u7528 DISTINCT<\/code> \u65f6\uff0c\u6570\u636e\u5e93\u4f1a\u5bf9\u7ed3\u679c\u96c6\u8fdb\u884c\u6392\u5e8f\u548c\u53bb\u91cd\u64cd\u4f5c\uff0c\u8fd9\u53ef\u80fd\u4f1a\u5f71\u54cd\u6027\u80fd\uff0c\u5c24\u5176\u662f\u5728\u6570\u636e\u91cf\u975e\u5e38\u5927\u7684\u65f6\u5019\u3002\u5982\u679c\u53ea\u9700\u8981\u5bf9\u67d0\u4e9b\u5217\u53bb\u91cd\uff0c\u5efa\u8bae\u53ea\u9009\u62e9\u90a3\u4e9b\u5fc5\u8981\u7684\u5217\uff0c\u907f\u514d\u67e5\u8be2\u4e2d\u5305\u542b\u4e0d\u5fc5\u8981\u7684\u5b57\u6bb5\u3002<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      5. \u4f18\u5316\u53bb\u91cd<\/strong><\/h3>\n\n\n\n
      \u5982\u679c\u67e5\u8be2\u6570\u636e\u91cf\u8f83\u5927\uff0c\u4e14\u9700\u8981\u53bb\u91cd\uff0c\u53ef\u4ee5\u8003\u8651\u4ee5\u4e0b\u65b9\u6cd5\u6765\u4f18\u5316\u6027\u80fd\uff1a<\/p>\n\n\n\n
        \n
      • \u4f7f\u7528\u7d22\u5f15<\/strong>\uff1a\u786e\u4fdd\u88ab\u67e5\u8be2\u7684\u5217\u4e0a\u6709\u7d22\u5f15\uff0c\u7279\u522b\u662f\u5f53\u4f60\u4f7f\u7528 DISTINCT<\/code> \u5bf9\u67d0\u4e2a\u5217\u8fdb\u884c\u53bb\u91cd\u65f6\uff0c\u7d22\u5f15\u80fd\u591f\u52a0\u901f\u53bb\u91cd\u8fc7\u7a0b\u3002<\/li>\n\n\n\n
      • \u67e5\u8be2\u7ed3\u679c\u5b57\u6bb5\u6700\u5c0f\u5316<\/strong>\uff1a\u53ea\u9009\u62e9\u5fc5\u8981\u7684\u5b57\u6bb5\u8fdb\u884c\u53bb\u91cd\uff0c\u800c\u4e0d\u662f\u5bf9\u6574\u4e2a\u8868\u8fdb\u884c\u53bb\u91cd\u3002<\/li>\n<\/ul>\n\n\n\n
        \u4f8b\u5982\uff1a<\/p>\n\n\n\n
        SELECT DISTINCT name FROM employees;<\/code><\/pre>\n\n\n\n
        \u5728\u8fd9\u91cc\uff0c\u5982\u679c name<\/code> \u5217\u4e0a\u6709\u7d22\u5f15\uff0c\u6570\u636e\u5e93\u53ef\u4ee5\u66f4\u5feb\u901f\u5730\u8bc6\u522b\u552f\u4e00\u7684 name<\/code>\u3002<\/p>\n\n\n\n
        \n\n\n\n
        6. \u53bb\u91cd\u548c\u6392\u5e8f<\/strong><\/h3>\n\n\n\n
        DISTINCT<\/code> \u548c ORDER BY<\/code> \u53ef\u4ee5\u7ed3\u5408\u4f7f\u7528\uff0c\u786e\u4fdd\u53bb\u91cd\u540e\u7684\u7ed3\u679c\u662f\u6709\u5e8f\u7684\u3002<\/p>\n\n\n\n
        6.1 \u53bb\u91cd\u5e76\u6392\u5e8f\uff1a<\/strong><\/h4>\n\n\n\n
        SELECT DISTINCT name FROM employees ORDER BY name;<\/code><\/pre>\n\n\n\n
        \u7ed3\u679c\uff1a<\/strong><\/p>\n\n\n\n
        name<\/th><\/tr><\/thead>
        Alice<\/td><\/tr>
        Bob<\/td><\/tr>
        Carol<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
        \u8fd9\u6837\u4f1a\u53bb\u9664\u91cd\u590d\u7684 name<\/code> \u5e76\u6309\u5b57\u6bcd\u987a\u5e8f\u5bf9\u7ed3\u679c\u6392\u5e8f\u3002<\/p>\n\n\n\n
        \n\n\n\n
        7. \u603b\u7ed3<\/strong><\/h3>\n\n\n\n
          \n
        • DISTINCT<\/code> \u7528\u4e8e\u4ece\u67e5\u8be2\u7ed3\u679c\u4e2d\u53bb\u9664\u91cd\u590d\u8bb0\u5f55\u3002<\/li>\n\n\n\n
        • \u53ef\u4ee5\u5355\u72ec\u5bf9\u67d0\u4e00\u5217\u8fdb\u884c\u53bb\u91cd\uff0c\u4e5f\u53ef\u4ee5\u5bf9\u591a\u4e2a\u5217\u7684\u7ec4\u5408\u8fdb\u884c\u53bb\u91cd\u3002<\/li>\n\n\n\n
        • \u5728\u52a8\u6001 SQL \u548c\u805a\u5408\u67e5\u8be2\u4e2d\uff0cDISTINCT<\/code> \u53ef\u4ee5\u5e2e\u52a9\u7b80\u5316\u903b\u8f91\uff0c\u907f\u514d\u91cd\u590d\u3002<\/li>\n\n\n\n
        • \u5bf9\u4e8e\u5927\u578b\u6570\u636e\u96c6\uff0cDISTINCT<\/code> \u4f1a\u6709\u6027\u80fd\u5f00\u9500\uff0c\u5efa\u8bae\u7ed3\u5408\u7d22\u5f15\u548c\u6700\u5c0f\u5316\u67e5\u8be2\u5b57\u6bb5\u6765\u4f18\u5316\u6027\u80fd\u3002<\/li>\n<\/ul>\n\n\n\n
          \u5e0c\u671b\u8fd9\u4e9b\u89e3\u91ca\u80fd\u5e2e\u52a9\u4f60\u66f4\u597d\u5730\u7406\u89e3 SQL \u4e2d\u7684\u53bb\u91cd\u64cd\u4f5c\uff01\u66f4\u591a\u8be6\u7ec6\u5185\u5bb9\u8bf7\u5173\u6ce8\u5176\u4ed6\u76f8\u5173\u6587\u7ae0\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
          \u5728 SQL \u67e5\u8be2\u4e2d\uff0c\u53bb\u91cd\u64cd\u4f5c\u4e3b\u8981\u901a\u8fc7 DISTINCT \u5173\u952e\u5b57\u6765\u5b9e\u73b0\uff0cDISTINCT \u7528\u4e8e\u79fb\u9664\u67e5\u8be2\u7ed3\u679c\u4e2d\u7684\u91cd […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[36],"tags":[],"class_list":["post-455","post","type-post","status-publish","format-standard","hentry","category-sql"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/455","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=455"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/455\/revisions"}],"predecessor-version":[{"id":456,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/455\/revisions\/456"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=455"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=455"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=455"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}