{"id":842,"date":"2025-02-18T18:23:08","date_gmt":"2025-02-18T10:23:08","guid":{"rendered":"https:\/\/eve2333.top\/?p=842"},"modified":"2025-06-21T14:36:43","modified_gmt":"2025-06-21T06:36:43","slug":"mysql%e6%95%b0%e6%8d%ae%e5%ba%93%e5%85%a5%e9%97%a8%e5%88%b0%e5%a4%a7%e8%9b%87%e5%b0%9a%e7%a1%85%e8%b0%b7%e5%ae%8b%e7%ba%a2%e5%ba%b7%e8%80%81%e5%b8%88%e7%ac%94%e8%ae%b0-%e5%9f%ba%e7%a1%80%e7%af%87-pa-4","status":"publish","type":"post","link":"https:\/\/eve2333.top\/?p=842","title":{"rendered":"MySQL\u6570\u636e\u5e93\u5165\u95e8\u5230\u5927\u86c7\u5c1a\u7845\u8c37\u5b8b\u7ea2\u5eb7\u8001\u5e08\u7b14\u8bb0 \u57fa\u7840\u7bc7 part 7"},"content":{"rendered":"\n

\u7b2c07\u7ae0_\u5355\u884c\u51fd\u6570<\/h1>\n\n\n\n

\u51fd\u6570\u5728\u8ba1\u7b97\u673a\u8bed\u8a00\u7684\u4f7f\u7528\u4e2d\u8d2f\u7a7f\u59cb\u7ec8\uff0c\u51fd\u6570\u7684\u4f5c\u7528\u662f\u4ec0\u4e48\u5462\uff1f\u5b83\u53ef\u4ee5\u628a\u6211\u4eec\u7ecf\u5e38\u4f7f\u7528\u7684\u4ee3\u7801\u5c01\u88c5\u8d77\u6765\uff0c \u9700\u8981\u7684\u65f6\u5019\u76f4\u63a5\u8c03\u7528\u5373\u53ef\u3002\u8fd9\u6837\u65e2 \u63d0\u9ad8\u4e86\u4ee3\u7801\u6548\u7387\uff0c\u53c8 \u63d0\u9ad8\u4e86\u53ef\u7ef4\u62a4\u6027\u3002\u5728 SQL \u4e2d\u6211\u4eec\u4e5f\u53ef\u4ee5\u4f7f\u7528\u51fd\u6570 \u5bf9\u68c0\u7d22\u51fa\u6765\u7684\u6570\u636e\u8fdb\u884c\u51fd\u6570\u64cd\u4f5c\u3002\u4f7f\u7528\u8fd9\u4e9b\u51fd\u6570\uff0c\u53ef\u4ee5\u6781\u5927\u5730 \u63d0\u9ad8\u7528\u6237\u5bf9\u6570\u636e\u5e93\u7684\u7ba1\u7406\u6548\u7387\u3002<\/p>\n\n\n\n

\u4ece\u51fd\u6570\u5b9a\u4e49\u7684\u89d2\u5ea6\u51fa\u53d1\uff0c\u6211\u4eec\u53ef\u4ee5\u5c06\u51fd\u6570\u5206\u6210 \u5185\u7f6e\u51fd\u6570\u548c \u81ea\u5b9a\u4e49\u51fd\u6570\u3002\u5728 SQL \u8bed\u8a00\u4e2d\uff0c\u540c\u6837\u4e5f\u5305\u62ec\u4e86 \u5185\u7f6e\u51fd\u6570\u548c\u81ea\u5b9a\u4e49\u51fd\u6570\u3002\u5185\u7f6e\u51fd\u6570\u662f\u7cfb\u7edf\u5185\u7f6e\u7684\u901a\u7528\u51fd\u6570\uff0c\u800c\u81ea\u5b9a\u4e49\u51fd\u6570\u662f\u6211\u4eec\u6839\u636e\u81ea\u5df1\u7684\u9700\u8981\u7f16\u5199 \u7684\uff0c\u672c\u7ae0\u53ca\u4e0b\u4e00\u7ae0\u8bb2\u89e3\u7684\u662f SQL \u7684\u5185\u7f6e\u51fd\u6570<\/strong>\u3002<\/p>\n\n\n\n

DBMS \u4e4b\u95f4\u7684\u5dee\u5f02\u6027\u5f88\u5927\uff0c\u8fdc\u5927\u4e8e\u540c\u4e00\u4e2a\u8bed\u8a00\u4e0d\u540c\u7248\u672c\u4e4b\u95f4\u7684\u5dee\u5f02\u3002\u5927\u90e8\u5206 DBMS \u4f1a\u6709\u81ea\u5df1\u7279\u5b9a\u7684\u51fd\u6570\uff0c\u8fd9\u5c31\u610f\u5473\u7740\u91c7\u7528 SQL \u51fd\u6570\u7684\u4ee3\u7801\u53ef\u79fb\u690d\u6027\u662f\u5f88 \u5dee\u7684\uff0c\u56e0\u6b64\u5728\u4f7f\u7528\u51fd\u6570\u7684\u65f6\u5019\u9700\u8981\u7279\u522b\u6ce8\u610f\u3002<\/p>\n\n\n\n

MySQL\u63d0\u4f9b\u7684\u5185\u7f6e\u51fd\u6570\u4ece \u5b9e\u73b0\u7684\u529f\u80fd\u89d2\u5ea6\u53ef\u4ee5\u5206\u4e3a\u6570\u503c\u51fd\u6570\u3001\u5b57\u7b26\u4e32\u51fd\u6570\u3001\u65e5\u671f\u548c\u65f6\u95f4\u51fd\u6570\u3001\u6d41\u7a0b\u63a7\u5236 \u51fd\u6570\u3001\u52a0\u5bc6\u4e0e\u89e3\u5bc6\u51fd\u6570\u3001\u83b7\u53d6MySQL\u4fe1\u606f\u51fd\u6570\u3001\u805a\u5408\u51fd\u6570\u7b49\u3002\u8fd9\u91cc\uff0c\u6211\u5c06\u8fd9\u4e9b\u4e30\u5bcc\u7684\u5185\u7f6e\u51fd\u6570\u518d\u5206\u4e3a\u4e24 \u7c7b\uff1a\u5355\u884c\u51fd\u6570\u3001 \u805a\u5408\u51fd\u6570\uff08\u6216\u5206\u7ec4\u51fd\u6570\uff09\u3002<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

 \u5355\u884c\u51fd\u6570<\/p>\n\n\n\n

    \n
  • \u64cd\u4f5c\u6570\u636e\u5bf9\u8c61<\/li>\n\n\n\n
  • \u63a5\u53d7\u53c2\u6570\u8fd4\u56de\u4e00\u4e2a\u7ed3\u679c<\/li>\n\n\n\n
  • \u53ea\u5bf9\u4e00\u884c\u8fdb\u884c\u53d8\u6362<\/strong><\/li>\n\n\n\n
  • \u6bcf\u884c\u8fd4\u56de\u4e00\u4e2a\u7ed3\u679c<\/strong><\/li>\n\n\n\n
  • \u53ef\u4ee5\u5d4c\u5957<\/li>\n\n\n\n
  • \u53c2\u6570\u53ef\u4ee5\u662f\u4e00\u5217\u6216\u4e00\u4e2a\u503c<\/li>\n<\/ul>\n\n\n\n

    2. \u6570\u503c\u51fd\u6570<\/h2>\n\n\n\n

    2.1 \u57fa\u672c\u51fd\u6570<\/h3>\n\n\n\n
    ABS(x)<\/td>\u8fd4\u56dex\u7684\u7edd\u5bf9\u503c<\/td><\/tr>
    SIGN(X)<\/td>\u8fd4\u56deX\u7684\u7b26\u53f7\u3002\u6b63\u6570\u8fd4\u56de1\uff0c\u8d1f\u6570\u8fd4\u56de-1\uff0c0\u8fd4\u56de0<\/td><\/tr>
    PI()<\/td>\u8fd4\u56de\u5706\u5468\u7387\u7684\u503c<\/td><\/tr>
    CEIL(x)\uff0cCEILING(x)<\/td>\u8fd4\u56de\u5927\u4e8e\u6216\u7b49\u4e8e\u67d0\u4e2a\u503c\u7684\u6700\u5c0f\u6574\u6570<\/td><\/tr>
    FLOOR(x)<\/td>\u8fd4\u56de\u5c0f\u4e8e\u6216\u7b49\u4e8e\u67d0\u4e2a\u503c\u7684\u6700\u5927\u6574\u6570<\/td><\/tr>
    LEAST(e1,e2,e3\u2026)<\/td>\u8fd4\u56de\u5217\u8868\u4e2d\u7684\u6700\u5c0f\u503c<\/td><\/tr>
    GREATEST(e1,e2,e3\u2026)<\/td>\u8fd4\u56de\u5217\u8868\u4e2d\u7684\u6700\u5927\u503c<\/td><\/tr>
    MOD(x,y)<\/td>\u8fd4\u56deX\u9664\u4ee5Y\u540e\u7684\u4f59\u6570<\/td><\/tr>
    RAND()<\/td>\u8fd4\u56de0~1\u7684\u968f\u673a\u503c<\/td><\/tr>
    RAND(x)<\/td>\u8fd4\u56de0~1\u7684\u968f\u673a\u503c\uff0c\u5176\u4e2dx\u7684\u503c\u7528\u4f5c\u79cd\u5b50\u503c\uff0c\u76f8\u540c\u7684X\u503c\u4f1a\u4ea7\u751f\u76f8\u540c\u7684\u968f\u673a \u6570<\/td><\/tr>
    ROUND(x)<\/td>\u8fd4\u56de\u4e00\u4e2a\u5bf9x\u7684\u503c\u8fdb\u884c\u56db\u820d\u4e94\u5165\u540e\uff0c\u6700\u63a5\u8fd1\u4e8eX\u7684\u6574\u6570<\/td><\/tr>
    ROUND(x,y)<\/td>\u8fd4\u56de\u4e00\u4e2a\u5bf9x\u7684\u503c\u8fdb\u884c\u56db\u820d\u4e94\u5165\u540e\u6700\u63a5\u8fd1X\u7684\u503c\uff0c\u5e76\u4fdd\u7559\u5230\u5c0f\u6570\u70b9\u540e\u9762Y\u4f4d<\/td><\/tr>
    TRUNCATE(x,y)<\/td>\u8fd4\u56de\u6570\u5b57x\u622a\u65ad\u4e3ay\u4f4d\u5c0f\u6570\u7684\u7ed3\u679c<\/td><\/tr>
    SQRT(x)<\/td>\u8fd4\u56dex\u7684\u5e73\u65b9\u6839\u3002\u5f53X\u7684\u503c\u4e3a\u8d1f\u6570\u65f6\uff0c\u8fd4\u56deNULL<\/td><\/tr>
    <\/td><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    \"\"<\/p>\n\n\n\n

    #\u5355\u884c\u51fd\u6570\u53ef\u4ee5\u5d4c\u5957\nSELECT TRUNCATE(ROUND(123.456,2),0)\nFROM DUAL;<\/code><\/pre>\n\n\n\n
    \u5f97\u5230123<\/p>\n\n\n\n
    2.2 \u89d2\u5ea6\u4e0e\u5f27\u5ea6\u4e92\u6362\u51fd\u6570<\/h3>\n\n\n\n
    RADIANS(x)\u5c06\u89d2\u5ea6\u8f6c\u5316\u4e3a\u5f27\u5ea6\uff0c\u5176\u4e2d\uff0c\u53c2\u6570x\u4e3a\u89d2\u5ea6\u503c<\/p>\n\n\n\n
    DEGREES(x) \u5c06\u5f27\u5ea6\u8f6c\u5316\u4e3a\u89d2\u5ea6\uff0c\u5176\u4e2d\uff0c\u53c2\u6570x\u4e3a\u5f27\u5ea6\u503c<\/p>\n\n\n\n
    SELECT RADIANS(30),RADIANS(60),RADIANS(90),\nDEGREES(2*PI()),DEGREES(RADIANS(90)) \nFROM DUAL;<\/code><\/pre>\n\n\n\n
    2.3 \u4e09\u89d2\u51fd\u6570<\/h3>\n\n\n\n
    SIN(x)<\/td>\u8fd4\u56dex\u7684\u6b63\u5f26\u503c\uff0c\u5176\u4e2d\uff0c\u53c2\u6570x\u4e3a\u5f27\u5ea6\u503c<\/td><\/tr>
    ASIN(x)<\/td>\u8fd4\u56dex\u7684\u53cd\u6b63\u5f26\u503c\uff0c\u5373\u83b7\u53d6\u6b63\u5f26\u4e3ax\u7684\u503c\u3002\u5982\u679cx\u7684\u503c\u4e0d\u5728-1\u52301\u4e4b\u95f4\uff0c\u5219\u8fd4\u56deNULL<\/td><\/tr>
    COS(x)<\/td>\u8fd4\u56dex\u7684\u4f59\u5f26\u503c\uff0c\u5176\u4e2d\uff0c\u53c2\u6570x\u4e3a\u5f27\u5ea6\u503c<\/td><\/tr>
    ACOS(x)<\/td>\u8fd4\u56dex\u7684\u53cd\u4f59\u5f26\u503c\uff0c\u5373\u83b7\u53d6\u4f59\u5f26\u4e3ax\u7684\u503c\u3002\u5982\u679cx\u7684\u503c\u4e0d\u5728-1\u52301\u4e4b\u95f4\uff0c\u5219\u8fd4\u56deNULL<\/td><\/tr>
    TAN(x)<\/td>\u8fd4\u56dex\u7684\u6b63\u5207\u503c\uff0c\u5176\u4e2d\uff0c\u53c2\u6570x\u4e3a\u5f27\u5ea6\u503c<\/td><\/tr>
    ATAN(x)<\/td>\u8fd4\u56dex\u7684\u53cd\u6b63\u5207\u503c\uff0c\u5373\u8fd4\u56de\u6b63\u5207\u503c\u4e3ax\u7684\u503c<\/td><\/tr>
    ATAN2(m,n)<\/td>\u8fd4\u56de\u4e24\u4e2a\u53c2\u6570\u7684\u53cd\u6b63\u5207\u503c<\/td><\/tr>
    COT(x)<\/td>\u8fd4\u56dex\u7684\u4f59\u5207\u503c\uff0c\u5176\u4e2d\uff0cX\u4e3a\u5f27\u5ea6\u503c<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    2.4 \u6307\u6570\u4e0e\u5bf9\u6570<\/h3>\n\n\n\n
     POW(x,y)\uff0cPOWER(X,Y)<\/td>\u8fd4\u56dex\u7684y\u6b21\u65b9<\/td><\/tr>
    EXP(X)<\/td>\u8fd4\u56dee\u7684X\u6b21\u65b9\uff0c\u5176\u4e2de\u662f\u4e00\u4e2a\u5e38\u6570\uff0c2.718281828459045<\/td><\/tr>
    LN(X)\uff0cLOG(X)<\/td>\u8fd4\u56de\u4ee5e\u4e3a\u5e95\u7684X\u7684\u5bf9\u6570\uff0c\u5f53X <= 0 \u65f6\uff0c\u8fd4\u56de\u7684\u7ed3\u679c\u4e3aNULL<\/td><\/tr>
    LOG10(X)<\/td>\u8fd4\u56de\u4ee510\u4e3a\u5e95\u7684X\u7684\u5bf9\u6570\uff0c\u5f53X <= 0 \u65f6\uff0c\u8fd4\u56de\u7684\u7ed3\u679c\u4e3aNULL<\/td><\/tr>
    LOG2(X)<\/td>\u8fd4\u56de\u4ee52\u4e3a\u5e95\u7684X\u7684\u5bf9\u6570\uff0c\u5f53X <= 0 \u65f6\uff0c\u8fd4\u56deNULL<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    2.5 \u8fdb\u5236\u95f4\u7684\u8f6c\u6362<\/h3>\n\n\n\n
    BIN(x)<\/td>\u8fd4\u56dex\u7684\u4e8c\u8fdb\u5236\u7f16\u7801<\/td><\/tr>
    HEX(x)<\/td>\u8fd4\u56dex\u7684\u5341\u516d\u8fdb\u5236\u7f16\u7801<\/td><\/tr>
    OCT(x)<\/td>\u8fd4\u56dex\u7684\u516b\u8fdb\u5236\u7f16\u7801<\/td><\/tr>
    CONV(x,f1,f2)<\/td>\u8fd4\u56def1\u8fdb\u5236\u6570\u53d8\u6210f2\u8fdb\u5236\u6570 <\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    | BIN(10) | HEX(10) | OCT(10) | CONV(10,2,8) |
       |+---------+---------+---------+--------------+ |
        1010   |        A       |       12     |      2           <\/p>\n\n\n\n
    3. \u5b57\u7b26\u4e32\u51fd\u6570<\/h2>\n\n\n\n
    ASCII(S)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32S\u4e2d\u7684\u7b2c\u4e00\u4e2a\u5b57\u7b26\u7684ASCII\u7801\u503c<\/td>CHAR_LENGTH(s)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32s\u7684\u5b57\u7b26\u6570\u3002\u4f5c\u7528\u4e0eCHARACTER_LENGTH(s)\u76f8\u540c<\/td><\/tr>
    LENGTH(s)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32s\u7684\u5b57\u8282\u6570\uff0c\u548c\u5b57\u7b26\u96c6\u6709\u5173<\/td>CONCAT(s1,s2,......,sn)<\/td>\u8fde\u63a5s1,s2,......,sn\u4e3a\u4e00\u4e2a\u5b57\u7b26\u4e32<\/td><\/tr>
    CONCAT_WS(x, s1,s2,......,sn)<\/td>\u540cCONCAT(s1,s2,...)\u51fd\u6570\uff0c\u4f46\u662f\u6bcf\u4e2a\u5b57\u7b26\u4e32\u4e4b\u95f4\u8981\u52a0\u4e0ax<\/td>INSERT(str, idx, len, replacestr)<\/td>\u5c06\u5b57\u7b26\u4e32str\u4ece\u7b2cidx\u4f4d\u7f6e\u5f00\u59cb\uff0clen\u4e2a\u5b57\u7b26\u957f\u7684\u5b50\u4e32\u66ff\u6362\u4e3a\u5b57\u7b26\u4e32replacestr<\/td><\/tr>
    REPLACE(str, a, b)<\/td>\u7528\u5b57\u7b26\u4e32b\u66ff\u6362\u5b57\u7b26\u4e32str\u4e2d\u6240\u6709\u51fa\u73b0\u7684\u5b57\u7b26\u4e32a<\/td>UPPER(s) \u6216 UCASE(s)<\/td>\u5c06\u5b57\u7b26\u4e32s\u7684\u6240\u6709\u5b57\u6bcd\u8f6c\u6210\u5927\u5199\u5b57\u6bcd<\/td><\/tr>
    LOWER(s) \u6216LCASE(s)<\/td>\u5c06\u5b57\u7b26\u4e32s\u7684\u6240\u6709\u5b57\u6bcd\u8f6c\u6210\u5c0f\u5199\u5b57\u6bcd<\/td>LEFT(str,n)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32str\u6700\u5de6\u8fb9\u7684n\u4e2a\u5b57\u7b26<\/td><\/tr>
    RIGHT(str,n)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32str\u6700\u53f3\u8fb9\u7684n\u4e2a\u5b57\u7b26<\/td>LPAD(str, len, pad)<\/td>\u7528\u5b57\u7b26\u4e32pad\u5bf9str\u6700\u5de6\u8fb9\u8fdb\u884c\u586b\u5145\uff0c\u76f4\u5230str\u7684\u957f\u5ea6\u4e3alen\u4e2a\u5b57\u7b26<\/td><\/tr>
    RPAD(str ,len, pad)<\/td>\u7528\u5b57\u7b26\u4e32pad\u5bf9str\u6700\u53f3\u8fb9\u8fdb\u884c\u586b\u5145\uff0c\u76f4\u5230str\u7684\u957f\u5ea6\u4e3alen\u4e2a\u5b57\u7b26<\/td>LTRIM(s)<\/td>\u53bb\u6389\u5b57\u7b26\u4e32s\u5de6\u4fa7\u7684\u7a7a\u683c<\/td><\/tr>
    RTRIM(s)<\/td>\u53bb\u6389\u5b57\u7b26\u4e32s\u53f3\u4fa7\u7684\u7a7a\u683c<\/td>TRIM(s)<\/td>\u53bb\u6389\u5b57\u7b26\u4e32s\u5f00\u59cb\u4e0e\u7ed3\u5c3e\u7684\u7a7a\u683c<\/td><\/tr>
    TRIM(s1 FROM s)<\/td>\u53bb\u6389\u5b57\u7b26\u4e32s\u5f00\u59cb\u4e0e\u7ed3\u5c3e\u7684s1<\/td>TRIM(LEADING s1 FROM s)<\/td>\u53bb\u6389\u5b57\u7b26\u4e32s\u5f00\u59cb\u5904\u7684s1<\/td><\/tr>
    TRIM(TRAILING s1 FROM s)<\/td>\u53bb\u6389\u5b57\u7b26\u4e32s\u7ed3\u5c3e\u5904\u7684s1<\/td>REPEAT(str, n)<\/td>\u8fd4\u56destr\u91cd\u590dn\u6b21\u7684\u7ed3\u679c<\/td><\/tr>
     SPACE(n)<\/td>\u8fd4\u56den\u4e2a\u7a7a\u683c<\/td>STRCMP(s1,s2)<\/td>\u6bd4\u8f83\u5b57\u7b26\u4e32s1,s2\u7684ASCII\u7801\u503c\u7684\u5927\u5c0f<\/td><\/tr>
    SUBSTR(s,index,len)<\/td>\u8fd4\u56de\u4ece\u5b57\u7b26\u4e32s\u7684index\u4f4d\u7f6e\u5176len\u4e2a\u5b57\u7b26\uff0c\u4f5c\u7528\u4e0eSUBSTRING(s,n,len)\u3001 MID(s,n,len)\u76f8\u540c<\/td>LOCATE(substr,str)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32substr\u5728\u5b57\u7b26\u4e32str\u4e2d\u9996\u6b21\u51fa\u73b0\u7684\u4f4d\u7f6e\uff0c\u4f5c\u7528\u4e8ePOSITION(substr IN str)\u3001INSTR(str,substr)\u76f8\u540c\u3002\u672a\u627e\u5230\uff0c\u8fd4\u56de0<\/td><\/tr>
    ELT(m,s1,s2,\u2026,sn)<\/td>\u8fd4\u56de\u6307\u5b9a\u4f4d\u7f6e\u7684\u5b57\u7b26\u4e32\uff0c\u5982\u679cm=1\uff0c\u5219\u8fd4\u56des1\uff0c\u5982\u679cm=2\uff0c\u5219\u8fd4\u56des2\uff0c\u5982 \u679cm=n\uff0c\u5219\u8fd4\u56desn<\/td>FIELD(s,s1,s2,\u2026,sn)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32s\u5728\u5b57\u7b26\u4e32\u5217\u8868\u4e2d\u7b2c\u4e00\u6b21\u51fa\u73b0\u7684\u4f4d\u7f6e <\/td><\/tr>
     FIND_IN_SET(s1,s2)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32s1\u5728\u5b57\u7b26\u4e32s2\u4e2d\u51fa\u73b0\u7684\u4f4d\u7f6e\u3002\u5176\u4e2d\uff0c\u5b57\u7b26\u4e32s2\u662f\u4e00\u4e2a\u4ee5\u9017\u53f7\u5206 \u9694\u7684\u5b57\u7b26\u4e32<\/td>REVERSE(s)<\/td>\u8fd4\u56des\u53cd\u8f6c\u540e\u7684\u5b57\u7b26\u4e32<\/td><\/tr>
    NULLIF(value1,value2)<\/td>\u6bd4\u8f83\u4e24\u4e2a\u5b57\u7b26\u4e32\uff0c\u5982\u679cvalue1\u4e0evalue2\u76f8\u7b49\uff0c\u5219\u8fd4\u56deNULL\uff0c\u5426\u5219\u8fd4\u56de value1<\/td><\/td><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
     \u6ce8\u610f\uff1aMySQL\u4e2d\uff0c\u5b57\u7b26\u4e32\u7684\u4f4d\u7f6e\u662f\u4ece1\u5f00\u59cb\u7684\u3002<\/strong><\/p>\n\n\n\n
    SELECT ASCII('Abcdfsf'),CHAR_LENGTH('hello'),CHAR_LENGTH('\u6211\u4eec'),\nLENGTH('hello'),LENGTH('\u6211\u4eec')\nFROM DUAL;\n\n# xxx worked for yyy\nSELECT CONCAT(emp.last_name,' worked for ',mgr.last_name) \"details\"\nFROM employees emp JOIN employees mgr\nWHERE emp.`manager_id` = mgr.employee_id;\n\nSELECT CONCAT_WS('-','hello','world','hello','beijing')\nFROM DUAL;\n#\u5b57\u7b26\u4e32\u7684\u7d22\u5f15\u662f\u4ece1\u5f00\u59cb\u7684\uff01\nSELECT INSERT('helloworld',2,3,'aaaaa'),REPLACE('hello','lol','mmm')\nFROM DUAL;\n\nSELECT UPPER('HelLo'),LOWER('HelLo')\nFROM DUAL;\n\nSELECT last_name,salary\nFROM employees\nWHERE LOWER(last_name) = 'King';\n\nSELECT LEFT('hello',2),RIGHT('hello',3),RIGHT('hello',13)\nFROM DUAL;\n\n# LPAD:\u5b9e\u73b0\u53f3\u5bf9\u9f50\u6548\u679c\n# RPAD:\u5b9e\u73b0\u5de6\u5bf9\u9f50\u6548\u679c\nSELECT employee_id,last_name,LPAD(salary,10,' ')\nFROM employees;\n\nSELECT CONCAT('---',LTRIM('    h  el  lo   '),'***'),\nTRIM('oo' FROM 'ooheollo')\nFROM DUAL;\n\nSELECT REPEAT('hello',4),LENGTH(SPACE(5)),STRCMP('abc','abe')\nFROM DUAL;\n\n\nSELECT SUBSTR('hello',2,2),LOCATE('lll','hello')\nFROM DUAL;\n\nSELECT ELT(2,'a','b','c','d'),FIELD('mm','gg','jj','mm','dd','mm'),\nFIND_IN_SET('mm','gg,mm,jj,dd,mm,gg')\nFROM DUAL;\n\nSELECT employee_id,NULLIF(LENGTH(first_name),LENGTH(last_name)) \"compare\"\nFROM employees;<\/code><\/pre>\n\n\n\n
    \"\" \"\"<\/p>\n\n\n\n
     4. \u65e5\u671f\u548c\u65f6\u95f4\u51fd\u6570<\/h2>\n\n\n\n
    4.1 \u83b7\u53d6\u65e5\u671f\u3001\u65f6\u95f4<\/h3>\n\n\n\n
    CURDATE() \uff0cCURRENT_DATE()<\/td>\u8fd4\u56de\u5f53\u524d\u65e5\u671f\uff0c\u53ea\u5305\u542b\u5e74\u3001 \u6708\u3001\u65e5<\/td><\/tr>
    CURTIME() \uff0c CURRENT_TIME()<\/td>\u8fd4\u56de\u5f53\u524d\u65f6\u95f4\uff0c\u53ea\u5305\u542b\u65f6\u3001 \u5206\u3001\u79d2<\/td><\/tr>
    NOW() \/ SYSDATE() \/ CURRENT_TIMESTAMP() \/ LOCALTIME() \/ LOCALTIMESTAMP()<\/td>\u8fd4\u56de\u5f53\u524d\u7cfb\u7edf\u65e5\u671f\u548c\u65f6\u95f4<\/td><\/tr>
    UTC_DATE()<\/td>\u8fd4\u56deUTC\uff08\u4e16\u754c\u6807\u51c6\u65f6\u95f4\uff09 \u65e5\u671f<\/td><\/tr>
    UTC_TIME()<\/td>\u8fd4\u56deUTC\uff08\u4e16\u754c\u6807\u51c6\u65f6\u95f4\uff09 \u65f6\u95f4<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \"\"<\/figure>\n\n\n\n
    4.2 \u65e5\u671f\u4e0e\u65f6\u95f4\u6233\u7684\u8f6c\u6362<\/h3>\n\n\n\n
    UNIX_TIMESTAMP()<\/td>\u4ee5UNIX\u65f6\u95f4\u6233\u7684\u5f62\u5f0f\u8fd4\u56de\u5f53\u524d\u65f6\u95f4\u3002SELECT UNIX_TIMESTAMP() >1634348884<\/td><\/tr>
    UNIX_TIMESTAMP(date)<\/td>\u5c06\u65f6\u95f4date\u4ee5UNIX\u65f6\u95f4\u6233\u7684\u5f62\u5f0f\u8fd4\u56de\u3002<\/td><\/tr>
    FROM_UNIXTIME(timestamp)<\/td>\u5c06UNIX\u65f6\u95f4\u6233\u7684\u65f6\u95f4\u8f6c\u6362\u4e3a\u666e\u901a\u683c\u5f0f\u7684\u65f6\u95f4<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \"\"<\/p>\n\n\n\n
    4.3 \u83b7\u53d6\u6708\u4efd\u3001\u661f\u671f\u3001\u661f\u671f\u6570\u3001\u5929\u6570\u7b49\u51fd\u6570<\/h3>\n\n\n\n
    YEAR(date) \/ MONTH(date) \/ DAY(date)<\/td>\u8fd4\u56de\u5177\u4f53\u7684\u65e5\u671f\u503c<\/td><\/tr>
    HOUR(time) \/ MINUTE(time) \/ SECOND(time)<\/td>\u8fd4\u56de\u5177\u4f53\u7684\u65f6\u95f4\u503c<\/td><\/tr>
    MONTHNAME(date)<\/td>\u8fd4\u56de\u6708\u4efd\uff1aJanuary\uff0c...<\/td><\/tr>
    DAYNAME(date)<\/td>\u8fd4\u56de\u661f\u671f\u51e0\uff1aMONDAY\uff0cTUESDAY.....SUNDAY<\/td><\/tr>
    WEEKDAY(date)<\/td>\u8fd4\u56de\u5468\u51e0\uff0c\u6ce8\u610f\uff0c\u54681\u662f0\uff0c\u54682\u662f1\uff0c\u3002\u3002\u3002\u5468\u65e5\u662f6<\/td><\/tr>
    QUARTER(date)<\/td>\u8fd4\u56de\u65e5\u671f\u5bf9\u5e94\u7684\u5b63\u5ea6\uff0c\u8303\u56f4\u4e3a1\uff5e4<\/td><\/tr>
    WEEK(date) \uff0c WEEKOFYEAR(date)<\/td>\u8fd4\u56de\u4e00\u5e74\u4e2d\u7684\u7b2c\u51e0\u5468<\/td><\/tr>
    DAYOFYEAR(date)<\/td>\u8fd4\u56de\u65e5\u671f\u662f\u4e00\u5e74\u4e2d\u7684\u7b2c\u51e0\u5929<\/td><\/tr>
    DAYOFMONTH(date)<\/td>\u8fd4\u56de\u65e5\u671f\u4f4d\u4e8e\u6240\u5728\u6708\u4efd\u7684\u7b2c\u51e0\u5929<\/td><\/tr>
    DAYOFWEEK(date)<\/td>\u8fd4\u56de\u5468\u51e0\uff0c\u6ce8\u610f\uff1a\u5468\u65e5\u662f1\uff0c\u5468\u4e00\u662f2\uff0c\u3002\u3002\u3002\u5468\u516d\u662f 7<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \"\"<\/figure>\n\n\n\n
    4.4 \u65e5\u671f\u7684\u64cd\u4f5c\u51fd\u6570<\/h3>\n\n\n\n
    EXTRACT(type FROM date) \u8fd4\u56de\u6307\u5b9a\u65e5\u671f\u4e2d\u7279\u5b9a\u7684\u90e8\u5206\uff0ctype\u6307\u5b9a\u8fd4\u56de\u7684\u503c<\/strong><\/p>\n\n\n\n
     EXTRACT(type FROM date)\u51fd\u6570\u4e2dtype\u7684\u53d6\u503c\u4e0e\u542b\u4e49\uff1a<\/p>\n\n\n\n
    MICROSECOND\u8fd4\u56de\u6beb\u79d2\u6570
    SECOND\u8fd4\u56de\u79d2\u6570
    MINUTE\u8fd4\u56de\u5206\u949f\u6570
    HOUR\u8fd4\u56de\u5c0f\u65f6\u6570
    DAY\u8fd4\u56de\u5929\u6570
    WEEK\u8fd4\u56de\u65e5\u671f\u5728\u4e00\u5e74\u4e2d\u7684\u7b2c\u51e0\u4e2a\u661f\u671f
    MONTH\u8fd4\u56de\u65e5\u671f\u5728\u4e00\u5e74\u4e2d\u7684\u7b2c\u51e0\u4e2a\u6708
    QUARTER\u8fd4\u56de\u65e5\u671f\u5728\u4e00\u5e74\u4e2d\u7684\u7b2c\u51e0\u4e2a\u5b63\u5ea6
    YEAR\u8fd4\u56de\u65e5\u671f\u7684\u5e74\u4efd
    SECOND_MICROSECOND\u8fd4\u56de\u79d2\u548c\u6beb\u79d2\u503c
    MINUTE_MICROSECOND\u8fd4\u56de\u5206\u949f\u548c\u6beb\u79d2\u503c
    MINUTE_SECOND\u8fd4\u56de\u5206\u949f\u548c\u79d2\u503c
    HOUR_MICROSECOND\u8fd4\u56de\u5c0f\u65f6\u548c\u6beb\u79d2\u503c
    HOUR_SECOND\u8fd4\u56de\u5c0f\u65f6\u548c\u79d2\u503c
    HOUR_MINUTE\u8fd4\u56de\u5c0f\u65f6\u548c\u5206\u949f\u503c
    DAY_MICROSECOND\u8fd4\u56de\u5929\u548c\u6beb\u79d2\u503c
    DAY_SECOND\u8fd4\u56de\u5929\u548c\u79d2\u503c
    DAY_MINUTE\u8fd4\u56de\u5929\u548c\u5206\u949f\u503c
    DAY_HOUR\u8fd4\u56de\u5929\u548c\u5c0f\u65f6
    YEAR MONTH\u8fd4\u56de\u5e74\u548c\u6708<\/p>\n\n\n\n
    \"\"<\/figure>\n\n\n\n
    4.5 \u65f6\u95f4\u548c\u79d2\u949f\u8f6c\u6362\u7684\u51fd\u6570<\/h3>\n\n\n\n
    TIME_TO_SEC(time)<\/td>\u5c06 time \u8f6c\u5316\u4e3a\u79d2\u5e76\u8fd4\u56de\u7ed3\u679c\u503c\u3002\u8f6c\u5316\u7684\u516c\u5f0f\u4e3a\uff1a\u5c0f\u65f6*3600+\u5206\u949f*60+\u79d2<\/td><\/tr>
    SEC_TO_TIME(seconds)<\/td>\u5c06 seconds \u63cf\u8ff0\u8f6c\u5316\u4e3a\u5305\u542b\u5c0f\u65f6\u3001\u5206\u949f\u548c\u79d2\u7684\u65f6\u95f4<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    4.6 \u8ba1\u7b97\u65e5\u671f\u548c\u65f6\u95f4\u7684\u51fd\u6570<\/h3>\n\n\n\n
    DATE_ADD(datetime, INTERVAL expr type)\uff0c ADDDATE(date,INTERVAL expr type)<\/td>\u8fd4\u56de\u4e0e\u7ed9\u5b9a\u65e5\u671f\u65f6\u95f4\u76f8\u5deeINTERVAL\u65f6 \u95f4\u6bb5\u7684\u65e5\u671f\u65f6\u95f4<\/td><\/tr>
    DATE_SUB(date,INTERVAL expr type)\uff0c SUBDATE(date,INTERVAL expr type)<\/td>\u8fd4\u56de\u4e0edate\u76f8\u5deeINTERVAL\u65f6\u95f4\u95f4\u9694\u7684 \u65e5\u671f<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \"\"<\/p>\n\n\n\n
    SELECT NOW(),DATE_ADD(NOW(),INTERVAL 1 YEAR),\nDATE_ADD(NOW(),INTERVAL -1 YEAR),\nDATE_SUB(NOW(),INTERVAL 1 YEAR)\nFROM DUAL;\n\n\nSELECT DATE_ADD(NOW(), INTERVAL 1 DAY) AS col1,DATE_ADD('2021-10-21 23:32:12',INTERVAL 1 SECOND) AS col2,\nADDDATE('2021-10-21 23:32:12',INTERVAL 1 SECOND) AS col3,\nDATE_ADD('2021-10-21 23:32:12',INTERVAL '1_1' MINUTE_SECOND) AS col4,\nDATE_ADD(NOW(), INTERVAL -1 YEAR) AS col5, #\u53ef\u4ee5\u662f\u8d1f\u6570\nDATE_ADD(NOW(), INTERVAL '1_1' YEAR_MONTH) AS col6 #\u9700\u8981\u5355\u5f15\u53f7\nFROM DUAL;<\/code><\/pre>\n\n\n\n
    ADDTIME(time1,time2)<\/td>\u8fd4\u56detime1\u52a0\u4e0atime2\u7684\u65f6\u95f4\u3002\u5f53time2\u4e3a\u4e00\u4e2a\u6570\u5b57\u65f6\uff0c\u4ee3\u8868\u7684\u662f \u79d2\uff0c\u53ef\u4ee5\u4e3a\u8d1f\u6570<\/td><\/tr>
    SUBTIME(time1,time2)<\/td>\u8fd4\u56detime1\u51cf\u53bbtime2\u540e\u7684\u65f6\u95f4\u3002\u5f53time2\u4e3a\u4e00\u4e2a\u6570\u5b57\u65f6\uff0c\u4ee3\u8868\u7684 \u662f\u79d2\uff0c\u53ef\u4ee5\u4e3a\u8d1f\u6570<\/td><\/tr>
    DATEDIFF(date1,date2)<\/td>\u8fd4\u56dedate1 - date2\u7684\u65e5\u671f\u95f4\u9694\u5929\u6570<\/td><\/tr>
    TIMEDIFF(time1, time2)<\/td>\u8fd4\u56detime1 - time2\u7684\u65f6\u95f4\u95f4\u9694<\/td><\/tr>
    FROM_DAYS(N)<\/td>\u8fd4\u56de\u4ece0000\u5e741\u67081\u65e5\u8d77\uff0cN\u5929\u4ee5\u540e\u7684\u65e5\u671f<\/td><\/tr>
    TO_DAYS(date)<\/td>\u8fd4\u56de\u65e5\u671fdate\u8ddd\u79bb0000\u5e741\u67081\u65e5\u7684\u5929\u6570<\/td><\/tr>
    LAST_DAY(date)<\/td>\u8fd4\u56dedate\u6240\u5728\u6708\u4efd\u7684\u6700\u540e\u4e00\u5929\u7684\u65e5\u671f<\/td><\/tr>
    MAKEDATE(year,n)<\/td>\u9488\u5bf9\u7ed9\u5b9a\u5e74\u4efd\u4e0e\u6240\u5728\u5e74\u4efd\u4e2d\u7684\u5929\u6570\u8fd4\u56de\u4e00\u4e2a\u65e5\u671f<\/td><\/tr>
    MAKETIME(hour,minute,second)<\/td>\u5c06\u7ed9\u5b9a\u7684\u5c0f\u65f6\u3001\u5206\u949f\u548c\u79d2\u7ec4\u5408\u6210\u65f6\u95f4\u5e76\u8fd4\u56de<\/td><\/tr>
    PERIOD_ADD(time,n)<\/td>\u8fd4\u56detime\u52a0\u4e0an\u540e\u7684\u65f6\u95f4<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    SELECT ADDTIME(NOW(),20),SUBTIME(NOW(),30),SUBTIME(NOW(),'1:1:3'),DATEDIFF(NOW(),'2021-10-01'),\nTIMEDIFF(NOW(),'2021-10-25 22:10:10'),FROM_DAYS(366),TO_DAYS('0000-12-25'),\nLAST_DAY(NOW()),MAKEDATE(YEAR(NOW()),32),MAKETIME(10,21,23),PERIOD_ADD(20200101010101,10)\nFROM DUAL;<\/code><\/pre>\n\n\n\n
    \"\"\/<\/figure>\n\n\n\n
    4.7 \u65e5\u671f\u7684\u683c\u5f0f\u5316\u4e0e\u89e3\u6790<\/h3>\n\n\n\n
    DATE_FORMAT(date,fmt)<\/td>\u6309\u7167\u5b57\u7b26\u4e32fmt\u683c\u5f0f\u5316\u65e5\u671fdate\u503c<\/td><\/tr>
    TIME_FORMAT(time,fmt)<\/td>\u6309\u7167\u5b57\u7b26\u4e32fmt\u683c\u5f0f\u5316\u65f6\u95f4time\u503c<\/td><\/tr>
    GET_FORMAT(date_type,format_type)<\/td>\u8fd4\u56de\u65e5\u671f\u5b57\u7b26\u4e32\u7684\u663e\u793a\u683c\u5f0f<\/td><\/tr>
    STR_TO_DATE(str, fmt)<\/td>\u6309\u7167\u5b57\u7b26\u4e32fmt\u5bf9str\u8fdb\u884c\u89e3\u6790\uff0c\u89e3\u6790\u4e3a\u4e00\u4e2a\u65e5\u671f<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    %Y<\/td>4\u4f4d\u6570\u5b57\u8868\u793a\u5e74\u4efd<\/td>%y<\/td>\u8868\u793a\u4e24\u4f4d\u6570\u5b57\u8868\u793a\u5e74\u4efd<\/td><\/tr>
    %M<\/td>\u6708\u540d\u8868\u793a\u6708\u4efd\uff08January,....\uff09<\/td>%m<\/td>\u4e24\u4f4d\u6570\u5b57\u8868\u793a\u6708\u4efd \uff0801,02,03\u3002\u3002\u3002\uff09<\/td><\/tr>
    %b<\/td>\u7f29\u5199\u7684\u6708\u540d\uff08Jan.\uff0cFeb.\uff0c....\uff09<\/td>%c<\/td>\u6570\u5b57\u8868\u793a\u6708\u4efd\uff081,2,3,...\uff09<\/td><\/tr>
    %D<\/td>\u82f1\u6587\u540e\u7f00\u8868\u793a\u6708\u4e2d\u7684\u5929\u6570 \uff081st,2nd,3rd,...\uff09<\/td>%d<\/td>\u4e24\u4f4d\u6570\u5b57\u8868\u793a\u6708\u4e2d\u7684\u5929\u6570(01,02...)<\/td><\/tr>
    %e<\/td>\u6570\u5b57\u5f62\u5f0f\u8868\u793a\u6708\u4e2d\u7684\u5929\u6570 \uff081,2,3,4,5.....\uff09<\/td><\/td><\/td><\/tr>
    %H<\/td>\u4e24\u4f4d\u6570\u5b57\u8868\u793a\u5c0f\u6570\uff0c24\u5c0f\u65f6\u5236 \uff0801,02..\uff09<\/td>%h \u548c%I<\/td>\u4e24\u4f4d\u6570\u5b57\u8868\u793a\u5c0f\u65f6\uff0c12\u5c0f\u65f6\u5236 \uff0801,02..\uff09<\/td><\/tr>
    %k<\/td>\u6570\u5b57\u5f62\u5f0f\u7684\u5c0f\u65f6\uff0c24\u5c0f\u65f6\u5236(1,2,3)<\/td>%l<\/td>\u6570\u5b57\u5f62\u5f0f\u8868\u793a\u5c0f\u65f6\uff0c12\u5c0f\u65f6\u5236 \uff081,2,3,4....\uff09<\/td><\/tr>
    %i<\/td>\u4e24\u4f4d\u6570\u5b57\u8868\u793a\u5206\u949f\uff0800,01,02\uff09<\/td>%S \u548c%s<\/td>\u4e24\u4f4d\u6570\u5b57\u8868\u793a\u79d2(00,01,02...)<\/td><\/tr>
    %W<\/td>\u4e00\u5468\u4e2d\u7684\u661f\u671f\u540d\u79f0\uff08Sunday...\uff09<\/td>%a<\/td>\u4e00\u5468\u4e2d\u7684\u661f\u671f\u7f29\u5199\uff08Sun.\uff0c Mon.,Tues.\uff0c..\uff09<\/td><\/tr>
    %w<\/td>\u4ee5\u6570\u5b57\u8868\u793a\u5468\u4e2d\u7684\u5929\u6570 (0=Sunday,1=Monday....<\/td><\/td><\/td><\/tr>
    %j<\/td>\u4ee53\u4f4d\u6570\u5b57\u8868\u793a\u5e74\u4e2d\u7684\u5929\u6570(001,002...)<\/td>%U<\/td>\u4ee5\u6570\u5b57\u8868\u793a\u5e74\u4e2d\u7684\u7b2c\u51e0\u5468\uff0c \uff081,2,3\u3002\u3002\uff09\u5176\u4e2dSunday\u4e3a\u5468\u4e2d\u7b2c\u4e00 \u5929<\/td><\/tr>
    %u<\/td>\u4ee5\u6570\u5b57\u8868\u793a\u5e74\u4e2d\u7684\u7b2c\u51e0\u5468\uff0c \uff081,2,3\u3002\u3002\uff09\u5176\u4e2dMonday\u4e3a\u5468\u4e2d\u7b2c\u4e00 \u5929<\/td><\/td><\/td><\/tr>
    %T<\/td>24\u5c0f\u65f6\u5236<\/td>%r<\/td>12\u5c0f\u65f6\u5236<\/td><\/tr>
    %p<\/td>AM\u6216PM<\/td>%%<\/td>\u8868\u793a%<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    #3.7 \u65e5\u671f\u7684\u683c\u5f0f\u5316\u4e0e\u89e3\u6790\n# \u683c\u5f0f\u5316\uff1a\u65e5\u671f ---> \u5b57\u7b26\u4e32\n# \u89e3\u6790\uff1a  \u5b57\u7b26\u4e32 ----> \u65e5\u671f\n\n#\u6b64\u65f6\u6211\u4eec\u8c08\u7684\u662f\u65e5\u671f\u7684\u663e\u5f0f\u683c\u5f0f\u5316\u548c\u89e3\u6790\n\n#\u4e4b\u524d\uff0c\u6211\u4eec\u63a5\u89e6\u8fc7\u9690\u5f0f\u7684\u683c\u5f0f\u5316\u6216\u89e3\u6790\nSELECT *\nFROM employees\nWHERE hire_date = '1993-01-13';\n\n#\u683c\u5f0f\u5316\uff1a\nSELECT DATE_FORMAT(CURDATE(),'%Y-%M-%D'),\nDATE_FORMAT(NOW(),'%Y-%m-%d'),TIME_FORMAT(CURTIME(),'%h:%i:%S'),\nDATE_FORMAT(NOW(),'%Y-%M-%D %h:%i:%S %W %w %T %r')\nFROM DUAL;\n\n#\u89e3\u6790\uff1a\u683c\u5f0f\u5316\u7684\u9006\u8fc7\u7a0b\nSELECT STR_TO_DATE('2021-October-25th 11:37:30 Monday 1','%Y-%M-%D %h:%i:%S %W %w')\nFROM DUAL;\n\nSELECT GET_FORMAT(DATE,'USA')\nFROM DUAL;\n\nSELECT DATE_FORMAT(CURDATE(),GET_FORMAT(DATE,'USA'))\nFROM DUAL;<\/code><\/pre>\n\n\n\n
    \u200b<\/p>\n\n\n\n
    \"\"\/<\/figure>\n\n\n\n
    \"\"\u770b\u770b\u5c31\u597d\uff0c\u5230\u65f6\u5019\u67e5\uff0c\"\"<\/p>\n\n\n\n
    5. \u6d41\u7a0b\u63a7\u5236\u51fd\u6570<\/h2>\n\n\n\n
    \u6d41\u7a0b\u5904\u7406\u51fd\u6570\u53ef\u4ee5\u6839\u636e\u4e0d\u540c\u7684\u6761\u4ef6\uff0c\u6267\u884c\u4e0d\u540c\u7684\u5904\u7406\u6d41\u7a0b\uff0c\u53ef\u4ee5\u5728SQL\u8bed\u53e5\u4e2d\u5b9e\u73b0\u4e0d\u540c\u7684\u6761\u4ef6\u9009\u62e9\u3002 MySQL\u4e2d\u7684\u6d41\u7a0b\u5904\u7406\u51fd\u6570\u4e3b\u8981\u5305\u62ecIF()\u3001IFNULL()\u548cCASE()\u51fd\u6570\u3002<\/p>\n\n\n\n
    IF(value,value1,value2)<\/td> \u5982\u679cvalue\u7684\u503c\u4e3aTRUE\uff0c\u8fd4\u56devalue1\uff0c \u5426\u5219\u8fd4\u56devalue2<\/td><\/tr>
    IFNULL(value1, value2)<\/td>\u5982\u679cvalue1\u4e0d\u4e3aNULL\uff0c\u8fd4\u56devalue1\uff0c\u5426\u5219\u8fd4\u56devalue2<\/td><\/tr>
    CASE WHEN \u6761\u4ef61 THEN \u7ed3\u679c1 WHEN \u6761\u4ef62 THEN \u7ed3\u679c2 .... [ELSE resultn] END<\/td>\u76f8\u5f53\u4e8eJava\u7684if...else if...else...<\/td><\/tr>
    CASE expr WHEN \u5e38\u91cf\u503c1 THEN \u503c1 WHEN \u5e38\u91cf\u503c1 THEN \u503c1 .... [ELSE \u503cn] END<\/td>\u76f8\u5f53\u4e8eJava\u7684switch...case...<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    #4.1 IF(VALUE,VALUE1,VALUE2)\n\nSELECT last_name,salary,IF(salary >= 6000,'\u9ad8\u5de5\u8d44','\u4f4e\u5de5\u8d44') \"details\"\nFROM employees;\n\nSELECT last_name,commission_pct,IF(commission_pct IS NOT NULL,commission_pct,0) \"details\",\nsalary * 12 * (1 + IF(commission_pct IS NOT NULL,commission_pct,0)) \"annual_sal\"\nFROM employees;<\/code><\/pre>\n\n\n\n
    <\/p>\n\n\n\n
    #4.3 CASE WHEN...THEN...WHEN...THEN...ELSE...END\n#\u7c7b\u4f3c\u4e8ejava\u7684ifelse if...elseif...else\nSELECTT last_name,\nsalary,\nCASE\n    WHEN salary >= 15000 THEN '\u767d\u9aa8\u7cbe'\n    WHEN salary >= 10000 THEN '\u6f5c\u529b\u80a1'\n    WHEN salary >= 8000 THEN '\u5c0f\u5c4c\u4e1d'\n    ELSE '\u8349\u6839' END \"details\",department_id\nFROM employees;<\/code><\/pre>\n\n\n\n
    #4.4 CASE ... WHEN ... THEN ... WHEN ... THEN ... ELSE ... END\n# \u7c7b\u4f3c\u4e8ejava\u7684swich ... case...\n\/*\n\n\u7ec3\u4e601\n\u67e5\u8be2\u90e8\u95e8\u53f7\u4e3a 10,20, 30 \u7684\u5458\u5de5\u4fe1\u606f, \n\u82e5\u90e8\u95e8\u53f7\u4e3a 10, \u5219\u6253\u5370\u5176\u5de5\u8d44\u7684 1.1 \u500d, \n20 \u53f7\u90e8\u95e8, \u5219\u6253\u5370\u5176\u5de5\u8d44\u7684 1.2 \u500d, \n30 \u53f7\u90e8\u95e8,\u6253\u5370\u5176\u5de5\u8d44\u7684 1.3 \u500d\u6570,\n\u5176\u4ed6\u90e8\u95e8,\u6253\u5370\u5176\u5de5\u8d44\u7684 1.4 \u500d\u6570\n\n*\/\nSELECT employee_id,last_name,department_id,salary,CASE department_id WHEN 10 THEN salary * 1.1\n\t\t\t\t\t\t\t\t     WHEN 20 THEN salary * 1.2\n\t\t\t\t\t\t\t\t     WHEN 30 THEN salary * 1.3\n\t\t\t\t\t\t\t\t     ELSE salary * 1.4 END \"details\"\nFROM employees;\n\n\/*\n\n\u7ec3\u4e602\n\u67e5\u8be2\u90e8\u95e8\u53f7\u4e3a 10,20, 30 \u7684\u5458\u5de5\u4fe1\u606f, \n\u82e5\u90e8\u95e8\u53f7\u4e3a 10, \u5219\u6253\u5370\u5176\u5de5\u8d44\u7684 1.1 \u500d, \n20 \u53f7\u90e8\u95e8, \u5219\u6253\u5370\u5176\u5de5\u8d44\u7684 1.2 \u500d, \n30 \u53f7\u90e8\u95e8\u6253\u5370\u5176\u5de5\u8d44\u7684 1.3 \u500d\u6570\n\n*\/\nSELECT employee_id,last_name,department_id,salary,CASE department_id WHEN 10 THEN salary * 1.1\n\t\t\t\t\t\t\t\t     WHEN 20 THEN salary * 1.2\n\t\t\t\t\t\t\t\t     WHEN 30 THEN salary * 1.3\n\t\t\t\t\t\t\t\t     END \"details\"\nFROM employees\nWHERE department_id IN (10,20,30);\n<\/code><\/pre>\n\n\n\n
    \u987a\u5e8f\u7ed3\u6784\uff0c\u5206\u652f\u7ed3\u6784\uff0c \u5faa\u73af\u7ed3\u6784\uff0c\u8fd9\u4e2a\u81ea\u5e26\u5faa\u73af\u3002\"\"<\/p>\n\n\n\n
    \u5176\u5b9e\u4ee5\u4e0b\u7684\u4e0d\u592a\u91cd\u8981\u4e86 <\/p>\n\n\n\n
    6. \u52a0\u5bc6\u4e0e\u89e3\u5bc6\u51fd\u6570<\/h2>\n\n\n\n
    \u52a0\u5bc6\u4e0e\u89e3\u5bc6\u51fd\u6570\u4e3b\u8981\u7528\u4e8e\u5bf9\u6570\u636e\u5e93\u4e2d\u7684\u6570\u636e\u8fdb\u884c\u52a0\u5bc6\u548c\u89e3\u5bc6\u5904\u7406\uff0c\u4ee5\u9632\u6b62\u6570\u636e\u88ab\u4ed6\u4eba\u7a83\u53d6\u3002\u8fd9\u4e9b\u51fd\u6570\u5728\u4fdd\u8bc1\u6570\u636e\u5e93\u5b89\u5168\u65f6\u975e\u5e38\u6709\u7528\u3002<\/p>\n\n\n\n
    \n
    \u4e00\u822c\u60c5\u51b5\u4e0b\uff0c\u524d\u7aef\u5c31\u4f1a\u5bf9\u6570\u636e\u8fdb\u884cmd5\u7684\u52a0\u5bc6\uff0c\u800c\u4e14\u4e3a\u4e86\u9632\u6b62\u6cc4\u9732\u53ef\u80fd\u4f1a\u591a\u6b21\u53cd\u8f6c\u3001\u622a\u53d6\u7684\u52a0\u5bc6\uff0c\u5728\u4f20\u7ed9\u540e\u53f0\u7684\u65f6\u5019\uff0c\u5df2\u7ecf\u662f\u52a0\u5bc6\u8fc7\u7684\uff0c\u8fd9\u4e5f\u9632\u6b62\u4e86\u5728\u7f51\u7edc\u8bf7\u6c42\u4e2d\uff0c\u5bc6\u7801\u6cc4\u9732<\/p>\n<\/blockquote>\n\n\n\n
    PASSWORD(str)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32str\u7684\u52a0\u5bc6\u7248\u672c\uff0c41\u4f4d\u957f\u7684\u5b57\u7b26\u4e32\u3002\u52a0\u5bc6\u7ed3\u679c \u4e0d\u53ef\u9006\uff0c\u5e38\u7528\u4e8e\u7528\u6237\u7684\u5bc6\u7801\u52a0\u5bc6\uff0c8.0\u5f00\u59cb\u5c31\u4e0d\u9002\u7528\u4e86\uff0c\u56de\u52305.7\u624d\u884c\u3002<\/strong><\/td><\/tr>
    MD5(str)<\/td>\u8fd4\u56de\u5b57\u7b26\u4e32str\u7684md5\u52a0\u5bc6\u540e\u7684\u503c\uff0c\u4e5f\u662f\u4e00\u79cd\u52a0\u5bc6\u65b9\u5f0f\u3002\u82e5\u53c2\u6570\u4e3a NULL\uff0c\u5219\u4f1a\u8fd4\u56deNULL<\/td><\/tr>
    SHA(str)<\/td>\u4ece\u539f\u660e\u6587\u5bc6\u7801str\u8ba1\u7b97\u5e76\u8fd4\u56de\u52a0\u5bc6\u540e\u7684\u5bc6\u7801\u5b57\u7b26\u4e32\uff0c\u5f53\u53c2\u6570\u4e3a NULL\u65f6\uff0c\u8fd4\u56deNULL\u3002 SHA\u52a0\u5bc6\u7b97\u6cd5\u6bd4MD5\u66f4\u52a0\u5b89\u5168\u3002<\/td><\/tr>
    ENCODE(value,password_seed)<\/td>\u8fd4\u56de\u4f7f\u7528password_seed\u4f5c\u4e3a\u52a0\u5bc6\u5bc6\u7801\u52a0\u5bc6value<\/td><\/tr>
    DECODE(value,password_seed)<\/td>\u8fd4\u56de\u4f7f\u7528password_seed\u4f5c\u4e3a\u52a0\u5bc6\u5bc6\u7801\u89e3\u5bc6value<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \u53ef\u4ee5\u770b\u5230\uff0cENCODE(value,password_seed)\u51fd\u6570\u4e0eDECODE(value,password_seed)\u51fd\u6570\u4e92\u4e3a\u53cd\u51fd\u6570\u3002 <\/p>\n\n\n\n
    7. MySQL\u4fe1\u606f\u51fd\u6570<\/h2>\n\n\n\n
    MySQL\u4e2d\u5185\u7f6e\u4e86\u4e00\u4e9b\u53ef\u4ee5\u67e5\u8be2MySQL\u4fe1\u606f\u7684\u51fd\u6570\uff0c\u8fd9\u4e9b\u51fd\u6570\u4e3b\u8981\u7528\u4e8e\u5e2e\u52a9\u6570\u636e\u5e93\u5f00\u53d1\u6216\u8fd0\u7ef4\u4eba\u5458\u66f4\u597d\u5730 \u5bf9\u6570\u636e\u5e93\u8fdb\u884c\u7ef4\u62a4\u5de5\u4f5c\u3002\u200b<\/p>\n\n\n\n
    \"\"\/<\/figure>\n\n\n\n
    8. \u5176\u4ed6\u51fd\u6570<\/h2>\n\n\n\n
    \u51fd\u6570\u7528\u6cd5
    FORMAT(value,n)\u8fd4\u56de\u5bf9\u6570\u5b57value\u8fdb\u884c\u683c\u5f0f\u5316\u540e\u7684\u7ed3\u679c\u6570\u636e\u3002n\u8868\u793a\u56db\u820d\u4e94\u5165\u540e\u4fdd\u7559\u5230\u5c0f\u6570\u70b9\u540en\u4f4d
    CONV(value,from,to)\u5c06value\u7684\u503c\u8fdb\u884c\u4e0d\u540c\u8fdb\u5236\u4e4b\u95f4\u7684\u8f6c\u6362
    INET_ATON(ipvalue)\u5c06\u4ee5\u70b9\u5206\u9694\u7684IP\u5730\u5740\u8f6c\u5316\u4e3a\u4e00\u4e2a\u6570\u5b57
    INET_NTOA(value)\u5c06\u6570\u5b57\u5f62\u5f0f\u7684IP\u5730\u5740\u8f6c\u5316\u4e3a\u4ee5\u70b9\u5206\u9694\u7684IP\u5730\u5740
    BENCHMARK(n,expr)\u5c06\u8868\u8fbe\u5f0fexpr\u91cd\u590d\u6267\u884cn\u6b21\u3002\u7528\u4e8e\u6d4b\u8bd5MySQL\u5904\u7406expr\u8868\u8fbe\u5f0f\u6240\u8017\u8d39
    \u7684\u65f6\u95f4
    CONVERT(value USINGchar_code)\u5c06value\u6240\u4f7f\u7528\u7684\u5b57\u7b26\u7f16\u7801\u4fee\u6539\u4e3achar_code<\/p>\n\n\n\n
    \u8bfe\u540e\u7ec3\u4e60<\/h2>\n\n\n\n
    \u3010\u9898\u76ee\u3011
    #1.\u663e\u793a\u7cfb\u7edf\u65f6\u95f4(\u6ce8\uff1a\u65e5\u671f+\u65f6\u95f4)
    #2.\u67e5\u8be2\u5458\u5de5\u53f7\uff0c\u59d3\u540d\uff0c\u5de5\u8d44\uff0c\u4ee5\u53ca\u5de5\u8d44\u63d0\u9ad8\u767e\u5206\u4e4b20%\u540e\u7684\u7ed3\u679c\uff08new salary)
    #3.\u5c06\u5458\u5de5\u7684\u59d3\u540d\u6309\u9996\u5b57\u6bcd\u6392\u5e8f\uff0c\u5e76\u5199\u51fa\u59d3\u540d\u7684\u957f\u5ea6\uff08length)
    # 4.\u67e5\u8be2\u5458\u5de5id,last_name,salary\uff0c\u5e76\u4f5c\u4e3a\u4e00\u4e2a\u5217\u8f93\u51fa\uff0c\u522b\u540d\u4e3aoUT_PUT
    #5.\u67e5\u8be2\u516c\u53f8\u5404\u5458\u5de5\u5de5\u4f5c\u7684\u5e74\u6570\u3001\u5de5\u4f5c\u7684\u5929\u6570\uff0c\u5e76\u6309\u5de5\u4f5c\u5e74\u6570\u7684\u964d\u5e8f\u6392\u5e8f
    #6.\u67e5\u8be2\u5458\u5de5\u59d3\u540d\uff0chire_date\uff0cdepartment_id\uff0c\u6ee1\u8db3\u4ee5\u4e0b\u6761\u4ef6\uff1a\u96c7\u7528\u65f6\u95f4\u57281997\u5e74\u4e4b\u540e\uff0cdepartment_id\u4e3a80 \u6216 90 \u6216110\uff0ccommission_pct\u4e0d\u4e3a\u7a7a
    #7.\u67e5\u8be2\u516c\u53f8\u4e2d\u5165\u804c\u8d85\u8fc710000\u5929\u7684\u5458\u5de5\u59d3\u540d\u3001\u5165\u804c\u65f6\u95f4
    #8.\u505a\u4e00\u4e2a\u67e5\u8be2\uff0c\u4ea7\u751f\u4e0b\u9762\u7684\u7ed3\u679c
    <last_name> earns <salary> monthly but wants <salary*3>\"\"#9.\u4f7f\u7528case-when\uff0c\u6309\u7167\u4e0b\u9762\u7684\u6761\u4ef6\uff1a
    job                 grade
    AD_PRES     A
    ST_MAN       B
    IT_PROG      C
    SA_REP        D
    ST_CLERK   E
    \u4ea7\u751f\u4e0b\u9762\u7684\u7ed3\u679c\uff1a<\/p>\n\n\n\n
    Last_name<\/td>Job_id<\/td>Grade<\/td><\/tr>
    king<\/td>AD_PRES<\/td>A<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
     1.\u663e\u793a\u7cfb\u7edf\u65f6\u95f4(\u6ce8\uff1a\u65e5\u671f+\u65f6\u95f4)<\/p>\n\n\n\n
    SELECT NOW(),SYSDATE(),CURRENT_TIMESTAMP(),LOCALTIME(),LOCALTIMESTAMP()\n#\u8fd9\u4e9b\u4efb\u9009\u4e00\u4e2a\u5373\u53ef\nFROM DUAL;<\/code><\/pre>\n\n\n\n
    2.\u67e5\u8be2\u5458\u5de5\u53f7\uff0c\u59d3\u540d\uff0c\u5de5\u8d44\uff0c\u4ee5\u53ca\u5de5\u8d44\u63d0\u9ad8\u767e\u5206\u4e4b20%\u540e\u7684\u7ed3\u679c\uff08new salary\uff09<\/p>\n\n\n\n
    SELECT employee_id, last_name, salary, salary * 1.2 \"new salary\" \nFROM employees;<\/code><\/pre>\n\n\n\n
    3.\u5c06\u5458\u5de5\u7684\u59d3\u540d\u6309\u9996\u5b57\u6bcd\u6392\u5e8f\uff0c\u5e76\u5199\u51fa\u59d3\u540d\u7684\u957f\u5ea6\uff08length\uff09<\/p>\n\n\n\n
    SELECT last_name, LENGTH(last_name) \nFROM employees\nORDER BY last_name DESC;<\/code><\/pre>\n\n\n\n
    4.\u67e5\u8be2\u5458\u5de5id,last_name,salary\uff0c\u5e76\u4f5c\u4e3a\u4e00\u4e2a\u5217\u8f93\u51fa\uff0c\u522b\u540d\u4e3aOUT_PUT<\/p>\n\n\n\n
    SELECT CONCAT(employee_id, ',' , last_name , ',', salary) OUT_PUT \nFROM employees;<\/code><\/pre>\n\n\n\n
    5.\u67e5\u8be2\u516c\u53f8\u5404\u5458\u5de5\u5de5\u4f5c\u7684\u5e74\u6570\u3001\u5de5\u4f5c\u7684\u5929\u6570\uff0c\u5e76\u6309\u5de5\u4f5c\u5e74\u6570\u7684\u964d\u5e8f\u6392\u5e8f\u3002<\/p>\n\n\n\n
    SELECT DATEDIFF(SYSDATE(), hire_date) \/ 365 worked_years, DATEDIFF(SYSDATE(), hire_date) worked_days\",\n######TO_DAYS(CURDATE())-TO_DAYS(hire_date\uff09\"worked_days1\"  \u4e5f\u53ef\u4ee5 \nFROM employees \nORDER BY worked_years DESC<\/code><\/pre>\n\n\n\n
    6.\u67e5\u8be2\u5458\u5de5\u59d3\u540d\uff0chire_date , department_id\uff0c\u6ee1\u8db3\u4ee5\u4e0b\u6761\u4ef6\uff1a\u96c7\u7528\u65f6\u95f4\u5728 1997\u5e74\u4e4b\u540e\uff0cdepartment_id \u4e3a80 \u6216 90 \u6216110, commission_pct\u4e0d\u4e3a\u7a7a<\/p>\n\n\n\n
    SELECT last_name, hire_date, department_id \nFROM employees \n#WHERE hire_date >= '1997-01-01' \n#WHERE hire_date >= STR_TO_DATE('1997-01-01', '%Y-%m-%d') \nWHERE DATE_FORMAT(hire_date,'%Y') >= '1997' \nAND department_id IN (80, 90, 110) \nAND commission_pct IS NOT NULL<\/code><\/pre>\n\n\n\n
    7.\u67e5\u8be2\u516c\u53f8\u4e2d\u5165\u804c\u8d85\u8fc710000\u5929\u7684\u5458\u5de5\u59d3\u540d\u3001\u5165\u804c\u65f6\u95f4<\/p>\n\n\n\n
    SELECT last_name,hire_date \nFROM employees \n#WHERE TO_DAYS(NOW()) - to_days(hire_date) > 10000; \nWHERE DATEDIFF(NOW(),hire_date) > 10000;<\/code><\/pre>\n\n\n\n
    8.\u505a\u4e00\u4e2a\u67e5\u8be2\uff0c\u4ea7\u751f\u4e0b\u9762\u7684\u7ed3\u679c.<\/p>\n\n\n\n
    38-\u7b2c7\u7ae0\u5355\u884c\u51fd\u6570\u8bfe\u540e\u7ec3\u4e60_\u54d4\u54e9\u54d4\u54e9_bilibili<\/a> \u200b<\/p>\n\n\n\n
    <\/p>\n","protected":false},"excerpt":{"rendered":"
    \u7b2c07\u7ae0_\u5355\u884c\u51fd\u6570 \u51fd\u6570\u5728\u8ba1\u7b97\u673a\u8bed\u8a00\u7684\u4f7f\u7528\u4e2d\u8d2f\u7a7f\u59cb\u7ec8\uff0c\u51fd\u6570\u7684\u4f5c\u7528\u662f\u4ec0\u4e48\u5462\uff1f\u5b83\u53ef\u4ee5\u628a\u6211\u4eec\u7ecf\u5e38\u4f7f\u7528\u7684\u4ee3\u7801\u5c01\u88c5\u8d77\u6765\uff0c \u9700\u8981\u7684\u65f6\u5019\u76f4\u63a5\u8c03\u7528 …<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"emotion":"","emotion_color":"","title_style":"","license":"","footnotes":""},"categories":[2],"tags":[16],"class_list":["post-842","post","type-post","status-publish","format-standard","hentry","category-2","tag-sql"],"_links":{"self":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts\/842","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=842"}],"version-history":[{"count":2,"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts\/842\/revisions"}],"predecessor-version":[{"id":1195,"href":"https:\/\/eve2333.top\/index.php?rest_route=\/wp\/v2\/posts\/842\/revisions\/1195"}],"wp:attachment":[{"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=842"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=842"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/eve2333.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=842"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}