SQL collation problems

This week I deployed a new feature and tried it on different SQL databases and was a bit suprised that on one database this error message came up:

Cannot resolve the collation conflict between "Latin1_General_CI_AS" and "SQL_Latin1_General_CP1_CI_AS" in the equal to operation.

This was strange, because - at least in theory - all databases have the same schema and I was sure that each database had the same collation setting.

Collations on columns

Well… my theory was wrong and this SQL statement told me that “some” columns had a different collation.

select sc.name, sc.collation_name from sys.columns sc
inner join sys.tables t on sc.object_id=t.object_id
where t.name='TABLENAME'

As it turns out, some columns had the collation Latin1_General_CI_AS and some had SQL_Latin1_General_CP1_CI_AS. I’m still not sure why, but I needed to do something.

How to change the collation

To change the collation you can execute something like this:

ALTER TABLE MyTable
ALTER COLUMN [MyColumn] NVARCHAR(200) COLLATE SQL_Latin1_General_CP1_CI_AS

Unfortunately there are restrictions and you can’t change the collation if the column is referenced by any one of the following:

• A computed column
• An index
• Distribution statistics, either generated automatically or by the CREATE STATISTICS statement
• A CHECK constraint
• A FOREIGN KEY constraint

Be aware: If you are not in control of the collation or if the collation is “fine” and you want to do this operation anyway, there might be a way to specify the collation in the SQL query.

For more information you might want to check out this Microsoft Docs “Set or Change the Column Collation”

Hope this helps!