{"id":1717,"date":"2025-02-16T08:43:29","date_gmt":"2025-02-16T00:43:29","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=1717"},"modified":"2025-02-16T08:43:29","modified_gmt":"2025-02-16T00:43:29","slug":"first-%e5%87%bd%e6%95%b0%e5%b8%b8%e8%a7%81%e9%97%ae%e9%a2%98%e5%8f%8a%e8%a7%a3%e5%86%b3%e6%8c%87%e5%8d%97","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/02\/16\/first-%e5%87%bd%e6%95%b0%e5%b8%b8%e8%a7%81%e9%97%ae%e9%a2%98%e5%8f%8a%e8%a7%a3%e5%86%b3%e6%8c%87%e5%8d%97\/","title":{"rendered":"FIRST() \u51fd\u6570\u5e38\u89c1\u95ee\u9898\u53ca\u89e3\u51b3\u6307\u5357"},"content":{"rendered":"\n

FIRST()<\/code> \u51fd\u6570\u867d\u7136\u5728\u4e00\u4e9b\u6570\u636e\u5e93\u7cfb\u7edf\u4e2d\u662f\u53ef\u7528\u7684\uff0c\u4f46\u5728\u5176\u4ed6\u7cfb\u7edf\uff08\u5982 MySQL\u3001PostgreSQL \u548c SQL Server \u7b49\uff09\u4e2d\u5e76\u4e0d\u652f\u6301\u3002\u56e0\u6b64\uff0c\u4f7f\u7528 FIRST()<\/code> \u51fd\u6570\u65f6\u53ef\u80fd\u4f1a\u9047\u5230\u4e00\u4e9b\u5e38\u89c1\u7684\u95ee\u9898\u3002\u4ee5\u4e0b\u662f FIRST()<\/code> \u51fd\u6570\u7684\u5e38\u89c1\u95ee\u9898\u53ca\u5176\u89e3\u51b3\u6307\u5357\u3002<\/p>\n\n\n\n

1. \u95ee\u9898\uff1a\u6570\u636e\u5e93\u4e0d\u652f\u6301 FIRST()<\/code> \u51fd\u6570<\/strong><\/h3>\n\n\n\n

\u539f\u56e0\uff1a<\/h4>\n\n\n\n

FIRST()<\/code> \u51fd\u6570\u5e76\u4e0d\u662f SQL \u6807\u51c6\u7684\u4e00\u90e8\u5206\uff0c\u6240\u4ee5\u5e76\u4e0d\u662f\u6240\u6709\u7684\u6570\u636e\u5e93\u7cfb\u7edf\u90fd\u652f\u6301\u5b83\u3002\u4f8b\u5982\uff0cMySQL\u3001PostgreSQL \u548c SQL Server \u4e2d\u90fd\u6ca1\u6709 FIRST()<\/code> \u51fd\u6570\u3002<\/p>\n\n\n\n

\u89e3\u51b3\u65b9\u6848\uff1a<\/h4>\n\n\n\n

\u5bf9\u4e8e\u4e0d\u652f\u6301 FIRST()<\/code> \u51fd\u6570\u7684\u6570\u636e\u5e93\uff0c\u4f60\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u65b9\u6cd5\u6a21\u62df\u76f8\u540c\u7684\u529f\u80fd\uff1a<\/p>\n\n\n\n

    \n
  • MySQL<\/strong> \u548c PostgreSQL<\/strong>\uff1a\u53ef\u4ee5\u4f7f\u7528 ORDER BY<\/code> \u548c LIMIT<\/code>\uff08\u6216 FETCH FIRST<\/code>\uff09\u6765\u83b7\u53d6\u6392\u5e8f\u540e\u7684\u7b2c\u4e00\u6761\u8bb0\u5f55\u3002<\/li>\n<\/ul>\n\n\n\n
      SELECT column_name\n  FROM table_name\n  ORDER BY column_name ASC\n  LIMIT 1;<\/code><\/pre>\n\n\n\n
      \n
    • SQL Server<\/strong>\uff1a\u53ef\u4ee5\u4f7f\u7528 TOP 1<\/code> \u6765\u83b7\u53d6\u7b2c\u4e00\u6761\u8bb0\u5f55\u3002<\/li>\n<\/ul>\n\n\n\n
        SELECT TOP 1 column_name\n  FROM table_name\n  ORDER BY column_name ASC;<\/code><\/pre>\n\n\n\n
      2. \u95ee\u9898\uff1aFIRST()<\/code> \u8fd4\u56de\u7684\u7ed3\u679c\u4e0e\u9884\u671f\u4e0d\u7b26<\/strong><\/h3>\n\n\n\n
      \u539f\u56e0\uff1a<\/h4>\n\n\n\n
      FIRST()<\/code> \u51fd\u6570\u7684\u884c\u4e3a\u5728\u4e0d\u540c\u7684\u6570\u636e\u5e93\u7cfb\u7edf\u4e2d\u53ef\u80fd\u4e0d\u540c\uff0c\u7279\u522b\u662f\u6392\u5e8f\u65b9\u5f0f\u3002\u4f8b\u5982\uff0c\u5728\u67d0\u4e9b\u6570\u636e\u5e93\u4e2d\uff0cFIRST()<\/code> \u53ef\u80fd\u4f1a\u8fd4\u56de\u8868\u4e2d\u7684\u7b2c\u4e00\u6761\u8bb0\u5f55\uff0c\u800c\u5728\u5176\u4ed6\u6570\u636e\u5e93\u4e2d\uff0c\u53ef\u80fd\u662f\u8fd4\u56de\u6309\u67d0\u4e2a\u5217\u6392\u5e8f\u540e\u7684\u7b2c\u4e00\u6761\u8bb0\u5f55\u3002<\/p>\n\n\n\n
      \u89e3\u51b3\u65b9\u6848\uff1a<\/h4>\n\n\n\n
      \u786e\u4fdd\u4f60\u5728\u67e5\u8be2\u4e2d\u4f7f\u7528\u4e86\u5408\u9002\u7684\u6392\u5e8f\u65b9\u5f0f\u3002\u5982\u679c\u4f60\u5e0c\u671b\u6309\u67d0\u5217\u6392\u5e8f\u540e\u83b7\u53d6\u7b2c\u4e00\u6761\u8bb0\u5f55\uff0c\u5e94\u8be5\u663e\u5f0f\u6307\u5b9a ORDER BY<\/code> \u5b50\u53e5\u3002\u4f8b\u5982\uff0c\u6309\u5de5\u8d44\uff08salary<\/code>\uff09\u5347\u5e8f\u6392\u5e8f\u5e76\u83b7\u53d6\u6700\u4f4e\u5de5\u8d44\uff1a<\/p>\n\n\n\n
      SELECT FIRST(salary)\nFROM employees\nORDER BY salary ASC;<\/code><\/pre>\n\n\n\n
      \u5982\u679c\u6570\u636e\u5e93\u4e0d\u652f\u6301 FIRST()<\/code>\uff0c\u53ef\u4ee5\u4f7f\u7528 LIMIT<\/code>\uff08\u6216 TOP<\/code>\uff09\u8fdb\u884c\u6a21\u62df\uff1a<\/p>\n\n\n\n
      SELECT salary\nFROM employees\nORDER BY salary ASC\nLIMIT 1;  -- \u6216 SQL Server \u4f7f\u7528 TOP 1<\/code><\/pre>\n\n\n\n
      3. \u95ee\u9898\uff1aFIRST()<\/code> \u8fd4\u56de NULL<\/code><\/strong><\/h3>\n\n\n\n
      \u539f\u56e0\uff1a<\/h4>\n\n\n\n
      \u5982\u679c\u8868\u4e2d\u6ca1\u6709\u4efb\u4f55\u6570\u636e\uff0c\u6216\u8005\u4f60\u4f7f\u7528\u4e86\u8fc7\u6ee4\u6761\u4ef6\uff0c\u5bfc\u81f4\u6ca1\u6709\u7b26\u5408\u6761\u4ef6\u7684\u8bb0\u5f55\uff0cFIRST()<\/code> \u53ef\u80fd\u4f1a\u8fd4\u56de NULL<\/code>\u3002<\/p>\n\n\n\n
      \u89e3\u51b3\u65b9\u6848\uff1a<\/h4>\n\n\n\n
        \n
      • \u786e\u4fdd\u67e5\u8be2\u7684\u6761\u4ef6\u6b63\u786e\uff0c\u4e14\u81f3\u5c11\u6709\u4e00\u884c\u7b26\u5408\u6761\u4ef6\u3002<\/li>\n\n\n\n
      • \u4f7f\u7528 COALESCE()<\/code> \u6216 IFNULL()<\/code> \u7b49\u51fd\u6570\u6765\u5904\u7406 NULL<\/code> \u8fd4\u56de\u503c\uff1a<\/li>\n<\/ul>\n\n\n\n
          SELECT COALESCE(FIRST(salary), 0) AS first_salary\n  FROM employees;<\/code><\/pre>\n\n\n\n
        \u6216\u8005\uff1a<\/p>\n\n\n\n
          SELECT IFNULL(FIRST(salary), 0) AS first_salary\n  FROM employees;<\/code><\/pre>\n\n\n\n
        4. \u95ee\u9898\uff1a\u67e5\u8be2\u4f7f\u7528 FIRST()<\/code> \u7ed3\u679c\u4e22\u5931\u6216\u4e0d\u7a33\u5b9a<\/strong><\/h3>\n\n\n\n
        \u539f\u56e0\uff1a<\/h4>\n\n\n\n
        FIRST()<\/code> \u51fd\u6570\u53ef\u80fd\u4f1a\u8fd4\u56de\u4e0d\u7a33\u5b9a\u7684\u7ed3\u679c\uff0c\u5c24\u5176\u662f\u5f53\u6ca1\u6709\u663e\u5f0f\u6307\u5b9a\u6392\u5e8f\u65f6\u3002\u6ca1\u6709\u6392\u5e8f\u7684\u60c5\u51b5\u4e0b\uff0c\u6570\u636e\u5e93\u7cfb\u7edf\u53ef\u80fd\u4f1a\u6309\u5185\u90e8\u6570\u636e\u5b58\u50a8\u7684\u987a\u5e8f\u8fd4\u56de\u7b2c\u4e00\u4e2a\u503c\uff0c\u800c\u8fd9\u4e2a\u987a\u5e8f\u53ef\u80fd\u662f\u4e0d\u53ef\u9884\u6d4b\u7684\u3002<\/p>\n\n\n\n
        \u89e3\u51b3\u65b9\u6848\uff1a<\/h4>\n\n\n\n
        \u59cb\u7ec8\u4f7f\u7528 ORDER BY<\/code> \u5b50\u53e5\u6765\u660e\u786e\u6307\u5b9a\u6392\u5e8f\u89c4\u5219\uff0c\u786e\u4fdd\u7ed3\u679c\u7684\u7a33\u5b9a\u6027\u3002\u4f8b\u5982\uff0c\u6309 employee_id<\/code> \u6392\u5e8f\u5e76\u83b7\u53d6\u7b2c\u4e00\u6761\u8bb0\u5f55\uff1a<\/p>\n\n\n\n
        SELECT FIRST(salary)\nFROM employees\nORDER BY employee_id ASC;<\/code><\/pre>\n\n\n\n
        \u5982\u679c\u6570\u636e\u5e93\u4e0d\u652f\u6301 FIRST()<\/code>\uff0c\u53ef\u4ee5\u4f7f\u7528 LIMIT<\/code> \u6216 TOP<\/code> \u6765\u4ee3\u66ff\uff0c\u5e76\u660e\u786e\u6392\u5e8f\uff1a<\/p>\n\n\n\n
        SELECT salary\nFROM employees\nORDER BY employee_id ASC\nLIMIT 1;  -- \u6216 SQL Server \u4f7f\u7528 TOP 1<\/code><\/pre>\n\n\n\n
        5. \u95ee\u9898\uff1aFIRST()<\/code> \u548c GROUP BY<\/code> \u4e00\u8d77\u4f7f\u7528\u65f6\u51fa\u73b0\u95ee\u9898<\/strong><\/h3>\n\n\n\n
        \u539f\u56e0\uff1a<\/h4>\n\n\n\n
        \u5728\u4f7f\u7528 GROUP BY<\/code> \u65f6\uff0c\u5982\u679c\u6ca1\u6709\u6b63\u786e\u5904\u7406\u6392\u5e8f\u6216\u6ca1\u6709\u6307\u5b9a\u5408\u9002\u7684\u5217\uff0cFIRST()<\/code> \u51fd\u6570\u7684\u7ed3\u679c\u53ef\u80fd\u4f1a\u51fa\u73b0\u9519\u8bef\uff0c\u5bfc\u81f4\u8fd4\u56de\u7684\u6570\u636e\u4e0d\u7b26\u5408\u9884\u671f\u3002<\/p>\n\n\n\n
        \u89e3\u51b3\u65b9\u6848\uff1a<\/h4>\n\n\n\n
        \u786e\u4fdd\u5728\u4f7f\u7528 GROUP BY<\/code> \u65f6\uff0c\u6b63\u786e\u5904\u7406\u6392\u5e8f\uff0c\u5e76\u660e\u786e\u6307\u5b9a\u8981\u83b7\u53d6\u7684\u201c\u7b2c\u4e00\u6761\u8bb0\u5f55\u201d\u3002\u4f8b\u5982\uff0c\u6309\u6bcf\u4e2a\u90e8\u95e8\u7684\u6700\u65e9\uff08\u6700\u5c0f\uff09\u5de5\u8d44\u6392\u5e8f\uff1a<\/p>\n\n\n\n
        SELECT department, FIRST(salary)\nFROM employees\nGROUP BY department\nORDER BY salary ASC;<\/code><\/pre>\n\n\n\n
        \u5982\u679c\u4f60\u7684\u6570\u636e\u5e93\u4e0d\u652f\u6301 FIRST()<\/code>\uff0c\u4f60\u53ef\u4ee5\u4f7f\u7528 LIMIT<\/code>\uff08\u6216 TOP 1<\/code>\uff09\u6765\u4ee3\u66ff\uff1a<\/p>\n\n\n\n
        SELECT department, salary\nFROM employees\nWHERE salary IN (\n  SELECT MIN(salary) FROM employees GROUP BY department\n);<\/code><\/pre>\n\n\n\n
        6. \u95ee\u9898\uff1aFIRST()<\/code> \u4e0e DISTINCT<\/code> \u914d\u5408\u4f7f\u7528\u65f6\u7684\u95ee\u9898<\/strong><\/h3>\n\n\n\n
        \u539f\u56e0\uff1a<\/h4>\n\n\n\n
        \u5728\u4e00\u4e9b\u6570\u636e\u5e93\u7cfb\u7edf\u4e2d\uff0cFIRST()<\/code> \u548c DISTINCT<\/code> \u4e00\u8d77\u4f7f\u7528\u65f6\uff0c\u53ef\u80fd\u4f1a\u51fa\u73b0\u610f\u5916\u7684\u7ed3\u679c\uff0c\u5c24\u5176\u662f\u5f53\u6709\u91cd\u590d\u6570\u636e\u65f6\u3002<\/p>\n\n\n\n
        \u89e3\u51b3\u65b9\u6848\uff1a<\/h4>\n\n\n\n
        \u4f7f\u7528 DISTINCT<\/code> \u65f6\uff0c\u786e\u4fdd\u6570\u636e\u5728\u805a\u5408\u4e4b\u524d\u5df2\u7ecf\u53bb\u91cd\u3002\u5982\u679c\u9700\u8981\u83b7\u53d6\u53bb\u91cd\u540e\u7684\u201c\u7b2c\u4e00\u4e2a\u201d\u8bb0\u5f55\uff0c\u53ef\u4ee5\u8003\u8651\u4f7f\u7528 GROUP BY<\/code> \u6216\u5728 ORDER BY<\/code> \u4e2d\u6307\u5b9a\u6392\u5e8f\u89c4\u5219\u6765\u4fdd\u8bc1\u6570\u636e\u7684\u6b63\u786e\u6027\u3002\u4f8b\u5982\uff0c\u83b7\u53d6\u6bcf\u4e2a\u90e8\u95e8\u7684\u7b2c\u4e00\u4e2a\u4e0d\u540c\u7684\u5de5\u8d44\uff1a<\/p>\n\n\n\n
        SELECT department, FIRST(salary)\nFROM (SELECT DISTINCT department, salary FROM employees) AS distinct_salaries\nGROUP BY department;<\/code><\/pre>\n\n\n\n
        7. \u95ee\u9898\uff1aFIRST()<\/code> \u4e0e\u5206\u9875\u67e5\u8be2\u4e00\u8d77\u4f7f\u7528\u65f6\u7684\u95ee\u9898<\/strong><\/h3>\n\n\n\n
        \u539f\u56e0\uff1a<\/h4>\n\n\n\n
        \u5f53\u4f7f\u7528\u5206\u9875\u67e5\u8be2\u65f6\uff0cFIRST()<\/code> \u53ef\u80fd\u4e0d\u7a33\u5b9a\uff0c\u56e0\u4e3a\u5b83\u4f9d\u8d56\u4e8e\u884c\u7684\u987a\u5e8f\u3002\u800c\u5206\u9875\u67e5\u8be2\u901a\u5e38\u4f9d\u8d56\u4e8e\u5206\u9875\u7684 OFFSET<\/code> \u548c LIMIT<\/code>\uff0c\u8fd9\u53ef\u80fd\u5bfc\u81f4\u8fd4\u56de\u4e0d\u4e00\u81f4\u7684\u7ed3\u679c\u3002<\/p>\n\n\n\n
        \u89e3\u51b3\u65b9\u6848\uff1a<\/h4>\n\n\n\n
        \u907f\u514d\u5728\u5206\u9875\u67e5\u8be2\u4e2d\u76f4\u63a5\u4f7f\u7528 FIRST()<\/code>\uff0c\u800c\u662f\u4f7f\u7528\u6807\u51c6\u7684\u6392\u5e8f\u548c LIMIT<\/code> \u6216 FETCH FIRST<\/code> \u6765\u4fdd\u8bc1\u8fd4\u56de\u4e00\u81f4\u7684\u7ed3\u679c\uff1a<\/p>\n\n\n\n
        SELECT salary\nFROM employees\nORDER BY salary ASC\nLIMIT 1 OFFSET 10;  -- \u4ece\u7b2c 11 \u6761\u8bb0\u5f55\u5f00\u59cb\uff0c\u83b7\u53d6\u4e0b\u4e00\u9875\u7684\u7b2c\u4e00\u6761\u8bb0\u5f55<\/code><\/pre>\n\n\n\n
        \u603b\u7ed3<\/h3>\n\n\n\n
          \n
        • \u4e0d\u652f\u6301\u7684\u6570\u636e\u5e93<\/strong>\uff1a\u5982\u679c\u6570\u636e\u5e93\u4e0d\u652f\u6301 FIRST()<\/code>\uff0c\u4f60\u53ef\u4ee5\u4f7f\u7528 ORDER BY<\/code> \u548c LIMIT<\/code>\uff08\u6216 TOP<\/code>\uff09\u6765\u5b9e\u73b0\u76f8\u540c\u7684\u529f\u80fd\u3002<\/li>\n\n\n\n
        • \u6392\u5e8f\u95ee\u9898<\/strong>\uff1a\u786e\u4fdd\u603b\u662f\u4f7f\u7528 ORDER BY<\/code> \u5b50\u53e5\u6765\u660e\u786e\u6307\u5b9a\u6392\u5e8f\u89c4\u5219\u3002<\/li>\n\n\n\n
        • NULL \u5904\u7406<\/strong>\uff1a\u786e\u4fdd\u8868\u4e2d\u6709\u6570\u636e\uff0c\u6216\u8005\u4f7f\u7528 COALESCE()<\/code> \u7b49\u51fd\u6570\u6765\u5904\u7406 NULL<\/code> \u503c\u3002<\/li>\n\n\n\n
        • GROUP BY \u95ee\u9898<\/strong>\uff1a\u5728\u4f7f\u7528 GROUP BY<\/code> \u65f6\uff0c\u786e\u4fdd\u6b63\u786e\u6392\u5e8f\uff0c\u5e76\u4f7f\u7528\u5408\u9002\u7684\u67e5\u8be2\u65b9\u5f0f\u6765\u8fd4\u56de\u6bcf\u7ec4\u7684\u7b2c\u4e00\u4e2a\u8bb0\u5f55\u3002<\/li>\n\n\n\n
        • <\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"
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