{"id":134,"date":"2019-07-22T21:29:47","date_gmt":"2019-07-22T13:29:47","guid":{"rendered":"http:\/\/www.cgh0610.cn\/?p=134"},"modified":"2019-07-22T21:35:42","modified_gmt":"2019-07-22T13:35:42","slug":"mysql%e7%94%a8%e6%88%b7%e5%8f%98%e9%87%8f","status":"publish","type":"post","link":"https:\/\/www.cgh0610.cn\/?p=134","title":{"rendered":"Mysql\u7528\u6237\u53d8\u91cf@"},"content":{"rendered":"

\u7528\u6237\u53d8\u91cf<\/h2>\n

\u53ef\u4ee5\u5148\u5728\u7528\u6237\u53d8\u91cf\u4e2d\u4fdd\u5b58\u503c\u7559\u5f85\u4ee5\u540e\u5f15\u7528\uff0c\u53ef\u4ee5\u5c06\u503c\u4ece\u4e00\u4e2a\u8bed\u53e5\u4e2d\u4f20\u9012\u5230\u53e6\u4e00\u4e2a\u8bed\u53e5\uff1b\u7528\u6237\u53d8\u91cf\u548c\u8fde\u63a5\u6709\u5173\uff0c\u6240\u4ee5\u5ba2\u6237\u7aef\u8fde\u63a5\u65ad\u5f00\u540e\u81ea\u52a8\u9500\u6bc1\u3002
\n\u7528\u6237\u53d8\u91cf\u7684\u5f62\u5f0f\u4e3a@var_name\uff0c\u5176\u4e2d\u53d8\u91cf\u540dvar_name\u53ef\u4ee5\u7531\u5f53\u524d\u5b57\u7b26\u96c6\u7684\u6587\u5b57\u6570\u5b57\u5b57\u7b26\u3001\u2018.\u2019\u3001\u2018_\u2019\u548c\u2018$\u2019\u7ec4\u6210\u3002 \u9ed8\u8ba4\u5b57\u7b26\u96c6\u662fcp1252 (Latin1)\u3002\u53ef\u4ee5\u7528mysqld\u7684–default-character-set\u9009\u9879\u66f4\u6539\u5b57\u7b26\u96c6\u3002\u53c2\u89c15.10.1\u8282\uff0c\u201c\u6570\u636e\u548c\u6392\u5e8f\u7528\u5b57\u7b26\u96c6\u201d\u3002\u7528\u6237\u53d8\u91cf\u540d\u5bf9\u5927\u5c0f\u5199\u4e0d\u654f\u611f\u3002<\/p>\n

\u9ed8\u8ba4\u503c<\/h3>\n

\u6ca1\u6709\u521d\u59cb\u5316\u7684\u7528\u6237\u53d8\u91cf\u9ed8\u8ba4\u4e3a NULL<\/strong>
\n\u5982\u679c\u7528\u6237\u53d8\u91cf\u5206\u914d\u4e86\u4e00\u4e2a\u5b57\u7b26\u4e32\u503c\uff0c\u5176\u5b57\u7b26\u96c6\u548c\u6821\u5bf9\u89c4\u5219\u4e0e\u8be5\u5b57\u7b26\u4e32\u7684\u76f8\u540c\u3002\u7528\u6237\u53d8\u91cf\u7684\u53ef\u538b\u7f29\u6027\uff08coercibility\uff09\u662f\u9690\u542b\u7684\u3002(\u5373\u4e3a\u8868\u5217\u503c\u7684\u76f8\u540c\u7684\u53ef\u538b\u7f29\u6027\uff08coercibility\uff09\u3002<\/p>\n

\u8bbe\u7f6e\u7528\u6237\u53d8\u91cf\u65b9\u6cd5<\/h3>\n

\u8bbe\u7f6e\u7528\u6237\u53d8\u91cf\u65b9\u6cd51<\/h4>\n

\u8bbe\u7f6e\u7528\u6237\u53d8\u91cf\u7684\u4e00\u4e2a\u9014\u5f84\u662f\u6267\u884cSET\u8bed\u53e5\uff1a<\/p>\n

SET @var_name = expr [, @var_name = expr] ...\n<\/code><\/pre>\n
\u5bf9\u4e8eSET\uff0c\u53ef\u4ee5\u4f7f\u7528=\u6216:=\u4f5c\u4e3a\u5206\u914d\u7b26\u3002\u5206\u914d\u7ed9\u6bcf\u4e2a\u53d8\u91cf\u7684expr\u53ef\u4ee5\u4e3a\u6574\u6570\u3001\u5b9e\u6570\u3001\u5b57\u7b26\u4e32\u6216\u8005NULL\u503c\u3002<\/p>\n
\u8bbe\u7f6e\u7528\u6237\u53d8\u91cf\u65b9\u6cd52<\/h4>\n
\u4e5f\u53ef\u4ee5\u7528\u8bed\u53e5\u4ee3\u66ffSET\u6765\u4e3a\u7528\u6237\u53d8\u91cf\u5206\u914d\u4e00\u4e2a\u503c\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u5206\u914d\u7b26\u5fc5\u987b\u4e3a:=\u800c\u4e0d\u80fd\u7528=\uff0c\u56e0\u4e3a\u5728\u975eSET\u8bed\u53e5\u4e2d=\u88ab\u89c6\u4e3a\u4e00\u4e2a\u6bd4\u8f83 \u64cd\u4f5c\u7b26\uff1a<\/p>\n
mysql> SET @t1=0, @t2=0, @t3=0;\nmysql> SELECT @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3;\n+----------------------+------+------+------+\n| @t1:=(@t2:=1)+@t3:=4 | @t1  | @t2  | @t3  |\n+----------------------+------+------+------+\n|                    5 |    5 |    1 |    4 |\n+----------------------+------+------+------+\n<\/code><\/pre>\n
\u7528\u6237\u53d8\u91cf\u7684\u8868\u8fbe\u5f0f\u7528\u6cd5<\/h3>\n
\u7528\u6237\u53d8\u91cf\u53ef\u7528\u5728\u8868\u8fbe\u5f0f\u4e2d\u3002\u76ee\u524d\u4e0d\u5305\u62ec\u660e\u663e\u9700\u8981\u6587\u5b57\u503c\u7684\u4e0a\u4e0b\u6587\u4e2d\uff0c\u4f8b\u5982SELECT\u8bed\u53e5\u7684LIMIT\u5b50\u53e5\uff0c\u6216\u8005LOAD DATA\u8bed\u53e5\u7684IGNORE number LINES\u5b50\u53e5\u3002<\/p>\n
\u6ce8\u91ca\uff1a\u5728SELECT\u8bed\u53e5\u4e2d\uff0c\u8868\u8fbe\u5f0f\u5728\u53d1\u9001\u5230\u5ba2\u6237\u7aef\u540e\u624d\u8ba1\u7b97\uff0c\u8fd9\u8bf4\u660e\u5728HAVING,GROUP BY,ORDER BY \u5b57\u53e5\u4e2d\uff0c\u4e0d\u80fd\u4f7f\u7528\u5305\u542bSELECT\u5217\u8868\u4e2d\u6240\u8bbe\u7684\u53d8\u91cf\u7684\u8868\u8fbe\u5f0f\u3002<\/strong>
\n\u4f8b\u5982\uff0c\u4e0b\u9762\u7684\u8bed\u53e5\u4e0d\u80fd\u6309\u671f\u671b\u5de5\u4f5c\uff1a<\/p>\n
mysql> SELECT (@aa:=id) AS a\uff0c(@aa+3) AS b FROM table HAVING b=5\uff1b\n<\/code><\/pre>\n
HAVING\u5b50\u53e5\u4e2d\u5f15\u7528\u4e86SELECT\u5217\u8868\u4e2d\u7684\u8868\u8fbe\u5f0f\u7684\u522b\u540d\uff0c\u4f7f\u7528@aa\u3002\u4e0d\u80fd\u6309\u671f\u671b\u5de5\u4f5c\uff1a@aa\u4e0d\u5305\u542b\u5f53\u524d\u884c\u7684\u503c\uff0c\u800c\u662f\u524d\u9762\u6240\u9009\u7684\u884c\u7684id\u503c\u3002<\/p>\n
\u4e00\u822c\u539f\u5219\u662f\u4e0d\u8981\u5728\u8bed\u53e5\u7684\u4e00\u4e2a\u90e8\u5206\u4e3a\u7528\u6237\u53d8\u91cf\u5206\u914d\u4e00\u4e2a\u503c\u800c\u5728\u540c\u4e00\u8bed\u53e5\u7684\u5176\u5b83\u90e8\u5206\u4f7f\u7528\u8be5\u53d8\u91cf\u3002<\/strong>\u53ef\u80fd\u4f1a\u5f97\u5230\u671f\u671b\u7684\u7ed3\u679c\uff0c\u4f46\u4e0d\u80fd\u4fdd\u8bc1\u3002<\/p>\n
\u8bbe\u7f6e\u53d8\u91cf\u5e76\u5728\u540c\u4e00\u8bed\u53e5\u4e2d\u4f7f\u7528\u5b83\u7684\u53e6\u4e00\u4e2a\u95ee\u9898\u662f\u53d8\u91cf\u7684\u9ed8\u8ba4\u7ed3\u679c\u7684\u7c7b\u578b\u53d6\u51b3\u4e8e\u8bed\u53e5\u524d\u9762\u7684\u53d8\u91cf\u7c7b\u578b\u3002<\/strong>
\n\u4e0b\u9762\u7684\u4f8b\u5b50\u8bf4\u660e\u4e86\u8be5\u70b9\uff1a<\/p>\n
mysql> SET @a='test';\nmysql> SELECT @a,(@a:=20) FROM tbl_name;\n<\/code><\/pre>\n
\u5bf9\u4e8e\u8be5 SELECT\u8bed\u53e5\uff0cMySQL\u5411\u5ba2\u6237\u7aef\u62a5\u544a\u7b2c1\u5217\u662f\u4e00\u4e2a\u5b57\u7b26\u4e32\uff0c\u5e76\u4e14\u5c06@a\u7684\u6240\u6709\u8bbf\u95ee\u8f6c\u6362\u4e3a\u5b57\u7b26\u4e32\uff0c\u5373\u4f7f@a\u5728\u7b2c2\u884c\u4e2d\u8bbe\u7f6e\u4e3a\u4e00\u4e2a\u6570\u5b57\u3002\u6267\u884c\u5b8cSELECT\u8bed\u53e5\u540e\uff0c@a\u88ab\u89c6\u4e3a\u4e0b\u4e00\u8bed\u53e5\u7684\u4e00\u4e2a\u6570\u5b57\u3002<\/p>\n
\u8981\u60f3\u907f\u514d\u8fd9\u79cd\u95ee\u9898\uff0c\u8981\u4e48\u4e0d\u5728\u540c\u4e00\u4e2a\u8bed\u53e5\u4e2d\u8bbe\u7f6e\u5e76\u4f7f\u7528\u76f8\u540c\u7684\u53d8\u91cf\uff0c\u8981\u4e48\u5728\u4f7f\u7528\u524d\u5c06\u53d8\u91cf\u8bbe\u7f6e\u4e3a0\u30010.0\u6216\u8005”\u4ee5\u5b9a\u4e49\u5176\u7c7b\u578b\u3002<\/p>\n
\u672a\u5206\u914d\u7684\u53d8\u91cf\u6709\u4e00\u4e2a\u503cNULL\uff0c\u7c7b\u578b\u4e3a\u5b57\u7b26\u4e32<\/p>\n
\n
\u7528\u6237\u53d8\u91cf\u5b9e\u8df5\uff1a<\/p>\n
\u7f16\u5199\u4e00\u4e2a SQL \u67e5\u8be2\uff0c\u67e5\u627e\u6240\u6709\u81f3\u5c11\u8fde\u7eed\u51fa\u73b0\u4e09\u6b21\u7684\u6570\u5b57\u3002\n\n+----+-----+\n| Id | Num |\n+----+-----+\n| 1  |  1  |\n| 2  |  1  |\n| 3  |  1  |\n| 4  |  2  |\n| 5  |  1  |\n| 6  |  2  |\n| 7  |  2  |\n+----+-----+\n\u4f8b\u5982\uff0c\u7ed9\u5b9a\u4e0a\u9762\u7684 Logs \u8868\uff0c 1 \u662f\u552f\u4e00\u8fde\u7eed\u51fa\u73b0\u81f3\u5c11\u4e09\u6b21\u7684\u6570\u5b57\u3002\n\n+-----------------+\n| ConsecutiveNums |\n+-----------------+\n| 1               |\n+-----------------+\n\n\u6765\u6e90\uff1a\u529b\u6263\uff08LeetCode\uff09\n\u94fe\u63a5\uff1ahttps:\/\/leetcode-cn.com\/problems\/consecutive-numbers\n\u8457\u4f5c\u6743\u5f52\u9886\u6263\u7f51\u7edc\u6240\u6709\u3002\u5546\u4e1a\u8f6c\u8f7d\u8bf7\u8054\u7cfb\u5b98\u65b9\u6388\u6743\uff0c\u975e\u5546\u4e1a\u8f6c\u8f7d\u8bf7\u6ce8\u660e\u51fa\u5904\u3002\n<\/code><\/pre>\n
\u9898\u89e3\uff1a<\/p>\n
#\u65b9\u6cd51 \n#\u8fde\u7eed\u51fa\u73b0\u7684\u610f\u5473\u7740\u76f8\u540c\u6570\u5b57\u7684 Id \u662f\u8fde\u7740\u7684\uff0c\u7531\u4e8e\u8fd9\u9898\u95ee\u7684\u662f\u81f3\u5c11\u8fde\u7eed\u51fa\u73b0 \n#3 \u6b21\uff0c\u6211\u4eec\u4f7f\u7528 Logs \u5e76\u68c0\u67e5\u662f\u5426\u6709 3 \u4e2a\u8fde\u7eed\u7684\u76f8\u540c\u6570\u5b57\u3002\n#\u5e76\u6dfb\u52a0\u5173\u952e\u5b57 DISTINCT \uff0c\u53bb\u9664\u91cd\u590d\u5143\u7d20\u3002\nSELECT DISTINCT\n    l1.Num AS ConsecutiveNums\nFROM\n    Logs l1,\n    Logs l2,\n    Logs l3\nWHERE\n    l1.Id = l2.Id - 1\n    AND l2.Id = l3.Id - 1\n    AND l1.Num = l2.Num\n    AND l2.Num = l3.Num\n#\u4f46\u662f\u4ee5\u4e0a\u65b9\u6cd5\u5b58\u5728\u4e00\u4e2a\u95ee\u9898\u5c31\u662f\uff0c\u5f53\u6570\u636e\u51fa\u73b0\u7269\u7406\u5220\u9664\u5bfc\u81f4ID\u4e0d\u8fde\u8d2f\u7684\u65f6\u5019\u4f1a\u51fa\u73b0\u5f02\u5e38\n\n#\u65b9\u6cd52\n#\u4f7f\u7528\u7528\u6237\u53d8\u91cf\uff0c\u7528cnt\u548cpre\u4e24\u4e2a\u53d8\u91cf\u6765\u7edf\u8ba1\nselect DISTINCT a.Num ConsecutiveNums from (\n    select t.Num,\n    @cnt:=IF(@pre=t.Num,@cnt+1,1) cnt,\n    @pre:=t.Num pre \n    from Logs t,(select @cnt:=0,@pre:=NULL) b ORDER BY t.Id asc) a\nwhere a.cnt>=3\n#\u6ee1\u8db3\u9898\u610f\uff0c\u5e76\u89e3\u51b3\u4e86\u6570\u636e\u7269\u7406\u5220\u540eID\u4e0d\u8fde\u7eed\u7684\u95ee\u9898\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
\u7528\u6237\u53d8\u91cf \u53ef\u4ee5\u5148\u5728\u7528\u6237\u53d8\u91cf\u4e2d\u4fdd\u5b58\u503c\u7559\u5f85\u4ee5\u540e\u5f15\u7528\uff0c\u53ef\u4ee5\u5c06\u503c\u4ece\u4e00\u4e2a\u8bed\u53e5\u4e2d\u4f20\u9012\u5230\u53e6\u4e00\u4e2a\u8bed\u53e5\uff1b\u7528\u6237\u53d8\u91cf\u548c\u8fde\u63a5\u6709\u5173\uff0c\u6240\u4ee5 … \u7ee7\u7eed\u9605\u8bfbMysql\u7528\u6237\u53d8\u91cf@<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"aside","meta":[],"categories":[39,12],"tags":[58,28,57],"_links":{"self":[{"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=\/wp\/v2\/posts\/134"}],"collection":[{"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=134"}],"version-history":[{"count":4,"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=\/wp\/v2\/posts\/134\/revisions"}],"predecessor-version":[{"id":137,"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=\/wp\/v2\/posts\/134\/revisions\/137"}],"wp:attachment":[{"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=134"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=134"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cgh0610.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=134"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}