T-SQL：如何创建区分大小写的唯一键？
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T-SQL: How do I create a unique key that is case sensitive?
提问by Seibar
How do I create a unique constraint on a varcharfield that is case sensitive (SQL Server 2005)?
如何在varchar区分大小写的字段 (SQL Server 2005)上创建唯一约束？
Currently my constraint looks like this:
目前我的约束看起来像这样：
alter table MyTable
add constraint UK_MyTable_MyUniqueKey unique nonclustered (MyCol)
When I try to insert the following two values, I get a "Violation of UNIQUE KEY constraint..." error.
当我尝试插入以下两个值时，出现“违反唯一键约束...”错误。
insert into MyTable (MyCol) values ('ABC')
insert into MyTable (MyCol) values ('abc') --causes a violation of UNIQUE KEY constraint 'UK_MyTable_MyUnqiueKey'
I would like the two differently-cased values to be handled as unqiue. I imagine it will involve the following code, but I do not know how it changes my add constraintsyntax.
我希望将两个不同大小写的值作为 unqiue 处理。我想它会涉及以下代码，但我不知道它如何改变我的add constraint语法。
COLLATE SQL_Latin1_General_CP1_CS_AS
回答by Jason Punyon
This will change the column to be case sensitive. I don't think there's any change to your constraint...
这会将列更改为区分大小写。我不认为你的约束有任何改变......
ALTER TABLE mytable
ALTER COLUMN mycolumn VARCHAR(10)
COLLATE SQL_Latin1_General_CP1_CS_AS
Any selects or joins on this column will become case sensitive as a result of this operation.
由于此操作，此列上的任何选择或连接都将区分大小写。
回答by dkretz
You can only set the case-sensitivity of the data in the database (smallest granularity of column). You can't set case-sensitivity of an index - that would be equivalent to being able to index on an expression, which is possible in some databases but not Sql Server.
您只能设置数据库中数据的大小写敏感度（列的最小粒度）。您不能设置索引的区分大小写 - 这相当于能够对表达式进行索引，这在某些数据库中是可能的，但在 Sql Server 中是可能的。
