SQL Server collation is an important concept that influences how information is stored, compared, and arranged in a database. It refers to a set of character and character encoding rules that determine the order of data, how data is matched, and how queries are executed.

Collation is configured at different levels in the SQL Server database engine, including the SQL Server instance, database, column, and query levels. Each level inherits the collation settings from the parent level by default.

SQL Server Instance Level Collation

The SQL Server instance level collation is the default collation for the system databases, such as master, tempdb, and model. It is set during the SQL Server installation and can be found using the following T-SQL query:

SELECT SERVERPROPERTY('collation') AS ServerCollation;

It’s important to note that if a user’s database has a different collation than the SQL Server instance collation, comparing tables between the user database and tempdb can result in an error.

Database Collation

The database collation is inherited from the SQL Server instance collation by default. However, if a user changes the default collation of a database, the collation of existing user-defined table columns will not be changed. New tables created in the database will have the new collation. It’s important to be cautious when joining tables with different collations in the same database, as it can lead to errors.

Column Level Collation

The column level collation is inherited from the database collation. If the database collation is changed, existing columns will retain their original collation, while new columns will have the new collation. To find the collation for a specific column, you can use the following T-SQL query:

SELECT OBJECT_NAME(OBJECT_ID), name AS ColumnName, collation_name AS ColumnCollation
FROM sys.columns
WHERE collation_name IS NOT NULL
AND OBJECT_NAME(OBJECT_ID) = 'your_table_name'
AND name = 'your_column_name';

Query Level Collation

Query level collation is useful when you want to override the collation of a column in a specific T-SQL query statement. It allows you to compare case-sensitive strings or handle collation mismatches. You can use the COLLATE keyword to specify the desired collation in the query. For example:

SELECT *
FROM table1
INNER JOIN table2
ON table1.column COLLATE Latin1_General_CS_AS = table2.column COLLATE Latin1_General_CS_AS;

Using query level collation can help resolve collation conflicts and ensure accurate comparison of data.

Conclusion

Understanding SQL Server collation is crucial for ensuring proper data storage, comparison, and query execution. It is important to carefully consider collation settings during SQL Server installation, server migration, or database migration. Collation conflicts can lead to errors and performance issues, but they can be resolved using query level collation. By paying attention to collation, you can avoid potential issues and ensure smooth database operations.