Doing a join across two databases with different collations on SQL Server and getting an error.

Question

I know, I know with what I wrote in the question I shouldn't be surprised. But my situation is slowly working on an inherited POS system and my predecessor apparently wasn't aware of JOINs so when I looked into one of the internal pages that loads for 60 seconds I see that it's a fairly quick, rewrite these 8 queries as one query with JOINs situation. Problem is that besides not knowing about JOINs he also seems to have had a fetish for multiple databases and surprise, surprise they use different collations. Fact of the matter is we use all "normal" latin characters that English speaking people would consider the entire alphabet and this whole thing will be out of use in a few months so a bandaid is all I need.

Long story short is I need some kind of method to cast to a single collation so I can compare two fields from two databases.

Exact error is:

Cannot resolve the collation conflict between "SQL_Latin1_General_CP850_CI_AI" and "SQL_Latin1_General_CP1_CI_AS" in the equal to operation.

Answer 1

You can use the collate clause in a query (I can't find my example right now, so my syntax is probably wrong - I hope it points you in the right direction)

select sone_field collate SQL_Latin1_General_CP850_CI_AI
  from table_1
    inner join table_2
      on (table_1.field collate SQL_Latin1_General_CP850_CI_AI = table_2.field)
  where whatever

Answer 2

From Books Online:

The COLLATE clause can be specified at several levels, including the following:

1.Creating or altering a database. You can use the COLLATE clause of the CREATE DATABASE or ALTER DATABASE statement to specify the default collation of the database. You can also specify a collation when you create a database using SQL Server Enterprise Manager. If you do not specify a collation, the database is assigned the default collation of the SQL Server instance.

2.Creating or altering a table column. You can specify collations for each character string column using the COLLATE clause of the CREATE TABLE or ALTER TABLE statement. You can also specify a collation when you create a table using SQL Server Enterprise Manager. If you do not specify a collation, the column is assigned the default collation of the database.

You can also use the database_default option in the COLLATE clause to specify that a column in a temporary table use the collation default of the current user database for the connection instead of tempdb.

3.Casting the collation of an expression. You can use the COLLATE clause to cast a character expression to a certain collation. Character literals and variables are assigned the default collation of the current database. Column references are assigned the definition collation of the column. For the collation of an expression, see Collation Precedence.

I think the 3rd option is the one you are looking for.

There is an example here:

http://blog.sqlauthority.com/2007/06/11/sql-server-cannot-resolve-collation-conflict-for-equal-to-operation/

Answer 3

A general purpose way is to coerce the collation to DATABASE_DEFAULT. This removes hardcoding the collation name which could change.

It's also useful for temp table and table variables, and where you may not know the server collation (eg you are a vendor placing your system on the customer's server)

select
    sone_field collate DATABASE_DEFAULT
from
    table_1
    inner join
    table_2 on table_1.field collate DATABASE_DEFAULT = table_2.field
where whatever