{"id":640,"date":"2025-01-01T11:09:08","date_gmt":"2025-01-01T03:09:08","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=640"},"modified":"2025-01-01T11:09:08","modified_gmt":"2025-01-01T03:09:08","slug":"%e6%80%8e%e6%a0%b7%e4%bb%8e%e9%80%97%e5%8f%b7%e5%88%86%e9%9a%94%e7%9a%84%e5%ad%97%e7%ac%a6%e4%b8%b2%e4%b8%ad%e6%8f%90%e5%8f%96%e7%ac%ac-n-%e4%b8%aa%e5%80%bc%ef%bc%8c%e5%b9%b6%e5%a4%84%e7%90%86","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/01\/01\/%e6%80%8e%e6%a0%b7%e4%bb%8e%e9%80%97%e5%8f%b7%e5%88%86%e9%9a%94%e7%9a%84%e5%ad%97%e7%ac%a6%e4%b8%b2%e4%b8%ad%e6%8f%90%e5%8f%96%e7%ac%ac-n-%e4%b8%aa%e5%80%bc%ef%bc%8c%e5%b9%b6%e5%a4%84%e7%90%86\/","title":{"rendered":"\u600e\u6837\u4ece\u9017\u53f7\u5206\u9694\u7684\u5b57\u7b26\u4e32\u4e2d\u63d0\u53d6\u7b2c n \u4e2a\u503c\uff0c\u5e76\u5904\u7406\u7a7a\u503c"},"content":{"rendered":"\n
\n

\u5728 Oracle PL\/SQL \u4e2d\uff0c\u4f60\u53ef\u4ee5\u4f7f\u7528\u591a\u79cd\u65b9\u6cd5\u4ece\u9017\u53f7\u5206\u9694\u7684\u5b57\u7b26\u4e32\u4e2d\u63d0\u53d6\u7b2c n \u4e2a\u503c\uff0c\u5e76\u5904\u7406\u7a7a\u503c\u3002\u5e38\u89c1\u7684\u65b9\u6cd5\u5305\u62ec\u4f7f\u7528 REGEXP_SUBSTR<\/code> \u51fd\u6570\u6216\u4f7f\u7528 SUBSTR<\/code> \u548c INSTR<\/code> \u7ed3\u5408\u7684\u65b9\u5f0f\u3002\u4e0b\u9762\u6211\u5c06\u8be6\u7ec6\u8bb2\u89e3\u8fd9\u4e9b\u65b9\u6cd5\u5e76\u5c55\u793a\u5982\u4f55\u5904\u7406\u7a7a\u503c\u7684\u60c5\u51b5\u3002<\/p>\n<\/blockquote>\n\n\n\n

\n\n\n\n

\u65b9\u6cd5 1\uff1a\u4f7f\u7528 REGEXP_SUBSTR<\/code> \u63d0\u53d6\u7b2c n \u4e2a\u503c<\/h3>\n\n\n\n

REGEXP_SUBSTR<\/code> \u51fd\u6570\u53ef\u4ee5\u7528\u6b63\u5219\u8868\u8fbe\u5f0f\u4ece\u5b57\u7b26\u4e32\u4e2d\u63d0\u53d6\u5b50\u4e32\u3002\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528\u6b63\u5219\u8868\u8fbe\u5f0f\u63d0\u53d6\u7b2c n \u4e2a\u9017\u53f7\u5206\u9694\u7684\u503c\u3002\u4e3a\u4e86\u5904\u7406\u7a7a\u503c\uff0c\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528 NVL<\/code> \u6216 COALESCE<\/code> \u51fd\u6570\u6765\u786e\u4fdd\u8fd4\u56de\u7684\u7ed3\u679c\u4e0d\u4e3a NULL<\/code>\u3002<\/p>\n\n\n\n

\u793a\u4f8b\uff1a\u63d0\u53d6\u7b2c n \u4e2a\u503c\u5e76\u5904\u7406\u7a7a\u503c<\/h4>\n\n\n\n

\u5047\u8bbe\u6709\u4e00\u4e2a\u9017\u53f7\u5206\u9694\u7684\u5b57\u7b26\u4e32 str = 'a,b,,d,e'<\/code>\uff0c\u6211\u4eec\u9700\u8981\u63d0\u53d6\u7b2c 3 \u4e2a\u503c\u5e76\u5904\u7406\u7a7a\u503c\u3002<\/p>\n\n\n\n

DECLARE\n    str VARCHAR2(100) := 'a,b,,d,e';\n    n   NUMBER := 3;  -- \u7b2cn\u4e2a\u503c\n    result VARCHAR2(100);\nBEGIN\n    -- \u63d0\u53d6\u7b2cn\u4e2a\u503c\uff0c\u5982\u679c\u4e3a\u7a7a\u5219\u8fd4\u56de 'No value'\n    result := REGEXP_SUBSTR(str, '[^,]+', 1, n);\n    -- \u5904\u7406\u7a7a\u503c\n    IF result IS NULL THEN\n        result := 'No value';\n    END IF;\n\n    DBMS_OUTPUT.PUT_LINE('The ' || n || 'th value is: ' || result);\nEND;<\/code><\/pre>\n\n\n\n
\u89e3\u91ca<\/strong>:<\/p>\n\n\n\n
    \n
  • REGEXP_SUBSTR(str, '[^,]+', 1, n)<\/code>\uff1a<\/li>\n\n\n\n
  • [^,]+<\/code> \u8868\u793a\u5339\u914d\u975e\u9017\u53f7\u7684\u4e00\u4e2a\u6216\u591a\u4e2a\u5b57\u7b26\u3002<\/li>\n\n\n\n
  • 1<\/code> \u8868\u793a\u4ece\u5b57\u7b26\u4e32\u7684\u7b2c\u4e00\u4e2a\u5b57\u7b26\u5f00\u59cb\u67e5\u627e\u3002<\/li>\n\n\n\n
  • n<\/code> \u8868\u793a\u6211\u4eec\u8981\u63d0\u53d6\u7684\u7b2c n \u4e2a\u5339\u914d\u9879\u3002<\/li>\n\n\n\n
  • \u5982\u679c REGEXP_SUBSTR<\/code> \u8fd4\u56de NULL<\/code>\uff0c\u5219\u8868\u793a\u8be5\u4f4d\u7f6e\u6ca1\u6709\u503c\uff0c\u63a5\u7740\u6211\u4eec\u4f7f\u7528 IF<\/code> \u8bed\u53e5\u5c06\u5176\u66ff\u6362\u4e3a 'No value'<\/code>\u3002<\/li>\n<\/ul>\n\n\n\n
    \u8f93\u51fa<\/strong>:<\/p>\n\n\n\n
    The 3rd value is: No value<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    \u65b9\u6cd5 2\uff1a\u4f7f\u7528 SUBSTR<\/code> \u548c INSTR<\/code> \u63d0\u53d6\u7b2c n \u4e2a\u503c<\/h3>\n\n\n\n
    \u5982\u679c\u4f60\u4e0d\u60f3\u4f7f\u7528\u6b63\u5219\u8868\u8fbe\u5f0f\uff0c\u53ef\u4ee5\u7ed3\u5408 SUBSTR<\/code> \u548c INSTR<\/code> \u51fd\u6570\u6765\u63d0\u53d6\u6307\u5b9a\u4f4d\u7f6e\u7684\u503c\u3002INSTR<\/code> \u53ef\u4ee5\u5e2e\u52a9\u4f60\u627e\u5230\u9017\u53f7\u7684\u4f4d\u7f6e\uff0c\u800c SUBSTR<\/code> \u7528\u4e8e\u63d0\u53d6\u5b50\u4e32\u3002<\/p>\n\n\n\n
    \u793a\u4f8b\uff1a\u63d0\u53d6\u7b2c n \u4e2a\u503c\u5e76\u5904\u7406\u7a7a\u503c<\/h4>\n\n\n\n
    \u5047\u8bbe\u6709\u4e00\u4e2a\u9017\u53f7\u5206\u9694\u7684\u5b57\u7b26\u4e32 str = 'a,b,,d,e'<\/code>\uff0c\u6211\u4eec\u9700\u8981\u63d0\u53d6\u7b2c 3 \u4e2a\u503c\u5e76\u5904\u7406\u7a7a\u503c\u3002<\/p>\n\n\n\n
    DECLARE\n    str VARCHAR2(100) := 'a,b,,d,e';\n    n   NUMBER := 3;  -- \u7b2cn\u4e2a\u503c\n    start_pos NUMBER;\n    result VARCHAR2(100);\nBEGIN\n    -- \u8ba1\u7b97\u7b2cn\u4e2a\u9017\u53f7\u7684\u4f4d\u7f6e\n    start_pos := 1;\n    FOR i IN 1..n-1 LOOP\n        start_pos := INSTR(str, ',', start_pos) + 1;\n    END LOOP;\n\n    -- \u63d0\u53d6\u7b2cn\u4e2a\u503c\n    result := SUBSTR(str, start_pos, INSTR(str || ',', ',', start_pos) - start_pos);\n\n    -- \u5904\u7406\u7a7a\u503c\n    IF result IS NULL OR result = '' THEN\n        result := 'No value';\n    END IF;\n\n    DBMS_OUTPUT.PUT_LINE('The ' || n || 'th value is: ' || result);\nEND;<\/code><\/pre>\n\n\n\n
    \u89e3\u91ca<\/strong>:<\/p>\n\n\n\n
      \n
    • INSTR(str, ',', start_pos)<\/code> \u7528\u4e8e\u67e5\u627e\u7b2c n-1<\/code> \u4e2a\u9017\u53f7\u7684\u4f4d\u7f6e\u3002<\/li>\n\n\n\n
    • \u4f7f\u7528 SUBSTR<\/code> \u63d0\u53d6\u4ece start_pos<\/code> \u5f00\u59cb\u5230\u4e0b\u4e00\u4e2a\u9017\u53f7\u4e4b\u95f4\u7684\u5185\u5bb9\u3002<\/li>\n\n\n\n
    • \u5982\u679c\u63d0\u53d6\u7684\u7ed3\u679c\u4e3a\u7a7a\u5b57\u7b26\u4e32\u6216 NULL<\/code>\uff0c\u5219\u5c06\u5176\u66ff\u6362\u4e3a 'No value'<\/code>\u3002<\/li>\n<\/ul>\n\n\n\n
      \u8f93\u51fa<\/strong>:<\/p>\n\n\n\n
      The 3rd value is: No value<\/code><\/pre>\n\n\n\n
      \n\n\n\n
      \u65b9\u6cd5 3\uff1a\u4f7f\u7528 REGEXP_COUNT<\/code> \u5224\u65ad\u662f\u5426\u6709\u7b2c n \u4e2a\u503c<\/h3>\n\n\n\n
      \u5982\u679c\u9700\u8981\u5224\u65ad\u4e00\u4e2a\u9017\u53f7\u5206\u9694\u7684\u5b57\u7b26\u4e32\u662f\u5426\u5305\u542b\u7b2c n \u4e2a\u503c\uff0c\u53ef\u4ee5\u4f7f\u7528 REGEXP_COUNT<\/code> \u6765\u7edf\u8ba1\u9017\u53f7\u51fa\u73b0\u7684\u6b21\u6570\uff0c\u5224\u65ad\u662f\u5426\u8d85\u8fc7\u4e86 n\u3002<\/p>\n\n\n\n
      \u793a\u4f8b\uff1a\u5224\u65ad\u662f\u5426\u6709\u7b2c n \u4e2a\u503c\u5e76\u5904\u7406\u7a7a\u503c<\/h4>\n\n\n\n
      DECLARE\n    str VARCHAR2(100) := 'a,b,,d,e';\n    n   NUMBER := 3;  -- \u7b2cn\u4e2a\u503c\n    result VARCHAR2(100);\nBEGIN\n    -- \u5224\u65ad\u662f\u5426\u6709\u7b2cn\u4e2a\u503c\n    IF REGEXP_COUNT(str, '[^,]+') >= n THEN\n        result := REGEXP_SUBSTR(str, '[^,]+', 1, n);\n    ELSE\n        result := 'No value';\n    END IF;\n\n    DBMS_OUTPUT.PUT_LINE('The ' || n || 'th value is: ' || result);\nEND;<\/code><\/pre>\n\n\n\n
      \u89e3\u91ca<\/strong>:<\/p>\n\n\n\n
        \n
      • REGEXP_COUNT(str, '[^,]+')<\/code> \u7edf\u8ba1 str<\/code> \u4e2d\u4ee5\u9017\u53f7\u5206\u9694\u7684\u975e\u7a7a\u5b57\u6bb5\u7684\u6570\u91cf\u3002<\/li>\n\n\n\n
      • \u5982\u679c n<\/code> \u5c0f\u4e8e\u7b49\u4e8e\u8ba1\u6570\u7684\u6570\u91cf\uff0c\u5219\u63d0\u53d6\u7b2c n<\/code> \u4e2a\u503c\uff0c\u5426\u5219\u8fd4\u56de 'No value'<\/code>\u3002<\/li>\n<\/ul>\n\n\n\n
        \u8f93\u51fa<\/strong>:<\/p>\n\n\n\n
        The 3rd value is: No value<\/code><\/pre>\n\n\n\n
        \n\n\n\n
        \u603b\u7ed3<\/h3>\n\n\n\n
          \n
        • \u65b9\u6cd5 1\uff1a\u4f7f\u7528 REGEXP_SUBSTR<\/code><\/strong>\uff1a\u7b80\u6d01\u4e14\u7075\u6d3b\uff0c\u80fd\u591f\u901a\u8fc7\u6b63\u5219\u8868\u8fbe\u5f0f\u63d0\u53d6\u6307\u5b9a\u4f4d\u7f6e\u7684\u503c\uff0c\u9002\u7528\u4e8e\u5904\u7406\u591a\u79cd\u5206\u9694\u7b26\u7684\u60c5\u51b5\u3002<\/li>\n\n\n\n
        • \u65b9\u6cd5 2\uff1a\u4f7f\u7528 SUBSTR<\/code> \u548c INSTR<\/code><\/strong>\uff1a\u9002\u7528\u4e8e\u4e0d\u4f9d\u8d56\u6b63\u5219\u8868\u8fbe\u5f0f\u7684\u573a\u666f\uff0c\u63d0\u4f9b\u4e86\u66f4\u591a\u7684\u53ef\u63a7\u6027\uff0c\u9002\u5408\u5904\u7406\u7b80\u5355\u7684\u5206\u9694\u7b26\u3002<\/li>\n\n\n\n
        • \u65b9\u6cd5 3\uff1a\u4f7f\u7528 REGEXP_COUNT<\/code><\/strong>\uff1a\u7528\u4e8e\u5224\u65ad\u5b57\u7b26\u4e32\u4e2d\u662f\u5426\u6709\u8db3\u591f\u7684\u503c\u6765\u63d0\u53d6\uff0c\u786e\u4fdd\u63d0\u53d6\u7ed3\u679c\u6709\u6548\u3002<\/li>\n<\/ul>\n\n\n\n
          \u4ee5\u4e0a\u4e09\u79cd\u65b9\u6cd5\u90fd\u53ef\u4ee5\u6709\u6548\u5730\u63d0\u53d6\u9017\u53f7\u5206\u9694\u5b57\u7b26\u4e32\u4e2d\u7684\u7b2c n \u4e2a\u503c\uff0c\u5e76\u5904\u7406\u7a7a\u503c\u3002\u4f60\u53ef\u4ee5\u6839\u636e\u5b9e\u9645\u9700\u6c42\u9009\u62e9\u9002\u5408\u7684\u65b9\u6cd5\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
          \u5728 Oracle PL\/SQL \u4e2d\uff0c\u4f60\u53ef\u4ee5\u4f7f\u7528\u591a\u79cd\u65b9\u6cd5\u4ece\u9017\u53f7\u5206\u9694\u7684\u5b57\u7b26\u4e32\u4e2d\u63d0\u53d6\u7b2c n \u4e2a\u503c\uff0c\u5e76\u5904\u7406\u7a7a\u503c\u3002\u5e38\u89c1\u7684 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[35],"tags":[],"class_list":["post-640","post","type-post","status-publish","format-standard","hentry","category-mysql"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/640","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=640"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/640\/revisions"}],"predecessor-version":[{"id":641,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/640\/revisions\/641"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=640"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=640"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=640"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}