SQL Server MAX（）问题 [英] SQL Server MAX() Problem

问题描述

select max(LACode) as M from dbo.tblLeaveApproval where len(LACode)=8

查询结果：

The query results :

LAC-8038

但如果我写的查询如下：

But If I write the query like :

select max(LACode) as M from dbo.tblLeaveApproval 

然后结果：

then it results :

LAC-999

请给我一个解决这个问题的方法。为什么会出现这种差异？

Please give me a solution of this problem. Why such kind of difference is occurs?

推荐答案

LACode 列中的数据被评估为字符串因此LAC-9 ...大于LAC-8 ......当你过滤长度时，你将看不到LAC-9xx值，因此LAC-8xxx将是更大的值。

The data in the LACode column is being evaluated as a string hence LAC-9... is bigger than LAC-8... and when you filter on the length then you will not see the LAC-9xx values hence LAC-8xxx will be the bigger value.

select MAX(CAST(SUBSTR(LACode,5) as integer)) from dbo.tblLeaveApproval;

返回'LAC - '前缀后的最大数字。

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