SQL SERVER – Cannot Resolve Collation Conflict For Equal to Operation

Cannot resolve collation conflict for equal to operation.

In MS SQL SERVER, the collation can be set at the column level. When compared to 2 different collation columns in the query, this error comes up.

SELECT ID
FROM ItemsTable
INNER JOIN AccountsTable
WHERE ItemsTable.Collation1Col = AccountsTable.Collation2Col

If columns ItemsTable.Collation1Col and AccountsTable.Collation2Col have different collation, it will generate the error “Cannot resolve collation conflict for equal to operation“.

To resolve the collation conflict add the following keywords around “=” operator.

SELECT ID
FROM ItemsTable
INNER JOIN AccountsTable
WHERE ItemsTable.Collation1Col COLLATE DATABASE_DEFAULT
= AccountsTable.Collation2Col COLLATE DATABASE_DEFAULT

Watch this quick video for resolution:

Collation can affect the following areas:

1. Where clauses
2. Join predicates
3. Functions
4. Databases (e.g. TempDB may be in a different collation database_default than the other databases some times)

Checkout following video how collation can change the order of the column:

Just like collation, there is another problem with SQL Server and that is related to Parameter Sniffing, I have written a detailed blog post about how the parameter sniffing can be resolved in SQL Server.

Here are some really good blog posts which you can read about parameter sniffing and how you can avoid the problem related to it.

• SQL SERVER – Parameter Sniffing Simplest Example
  In this blog post, we discuss what actually is parameter sniffing and how we can overcome it with the help of recompiling the stored procedure.
• SQL SERVER – Parameter Sniffing and Local Variable in SP
  It is easy to overcome the parameter sniffing for the stored procedure by declaring the local variable inside the stored procedure.
• SQL SERVER – Parameter Sniffing and OPTIMIZE FOR UNKNOWN
  You can take advantage of the new query hint of Optimize For Unknown to simulate the local variable in the stored procedure. A very underutilized technique indeed.
• SQL SERVER – DATABASE SCOPED CONFIGURATION – PARAMETER SNIFFING
  This new database level enhancement was introduced recently which can help you overcome any issue with the parameter sniffing.
• SQL SERVER – Parameter Sniffing and OPTION (RECOMPILE)
  The oldest and most traditional technique to not cache the query plans and compile your stored procedure or queries every single time to get optimal performance.
• Performance and Recompiling Query – Summary
  This post summarizes the entire series of parameter sniffing, performance and recompiling query.

Reference: Pinal Dave (https://blog.sqlauthority.com)