[英]Mysql PHP Select with multiple values, MAX(LENGTH())
你好朋友我正在查询以获取注册表列表,但我需要获取重复的条目,并保留只有更长的
示例表:
ID = INT Auto increment
IDref = INT not null
UserId = INT ZeroFill
+--------+---------+--------+---------+
| ID | IDref | UserId | |
+--------+---------+--------+---------+
| 1 | 1 | 00001 | |
| 3 | 1 | 001 | |
| 4 | 1 | 002 | |
| 5 | 2 | 00001 | |
| 6 | 2 | 001 | |
| 7 | 2 | 002 | |
| 8 | 3 | 00001 | |
| 9 | 4 | 002 | |
+--------+---------+--------+---------+
查询
SELECT ID, IDref, UserId
FROM Table
WHERE UserId = '00001' OR '002'
GROUP BY IDref
HAVING count(IDref) > 0
ORDER BY CHAR_LENGTH(UserId ) DESC
LIMIT 1
更新我正在接受
+--------+---------+--------+---------+
| ID | IDref | UserId | |
+--------+---------+--------+---------+
| 4 | 1 | 002 | |
+--------+---------+--------+---------+
我需要这个输出:
+--------+---------+--------+---------+
| ID | IDref | UserId | |
+--------+---------+--------+---------+
| 1 | 1 | 00001 | |
| 5 | 2 | 00001 | |
| 8 | 3 | 00001 | |
| 9 | 4 | 002 | |//count(IDref) > 0// one registry find.
+--------+---------+--------+---------+
但不能正常工作我的查询。 有人可以帮助我。
工作代码的最后更新感谢Barmar:
SELECT t1.ID, t1.IDref, t1.UserId
FROM Table1 AS t1
JOIN (SELECT IDref, MAX(LENGTH(UserId)) AS maxlength
FROM Table1
WHERE UserID IN ('00001', '002')
GROUP BY IDref) AS t2
ON t1.IDref = t2.IDref AND LENGTH(t1.UserId) = t2.maxlength
WHERE t1.UserId IN ('00001', '002')
好吧,但是你可以看到这个查询在具有20,000条记录的表格中的表现会更快吗?
WHERE UserId = '00001' OR '002'
不是测试列是否与这些值匹配的正确方法。 正确的方法是
WHERE UserId IN ('00001', '002')
你的代码相当于
WHERE (UserId = '00001') OR '002'
这总是正确的,因为'002'
不是假的。
你也应该删除LIMIT 1
。 否则,您只会获得一个具有重复项的IDRef
。
ORDER BY LENGTH(UserId)
不会使分组值选择具有最长长度的行 - 在分组后进行排序,并且分组只是任意选择其中一个值。 为此,您需要使用SQL中的一种技术仅选择列上具有最大值的行
SELECT t1.ID, t1.IDref, t1.UserId
FROM Table1 AS t1
JOIN (SELECT IDref, MAX(LENGTH(UserId)) AS maxlength
FROM Table1
WHERE UserID IN ('00001', '002')
GROUP BY IDref) AS t2
ON t1.IDref = t2.IDref AND LENGTH(t1.UserId) = t2.maxlength
WHERE t1.UserId IN ('00001', '002')
HAVING COUNT(IDRef) > 0
不需要,因为count总是大于0。
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