Fix Slow SQL Server Cross-Database Queries

There are various reasons that may cause slow cross-database queries in SQL Server, below are some possible solutions:

1. Use appropriate indexes: make sure that proper indexes are created on tables involved in cross-database queries to improve query performance.
2. Utilize appropriate join methods: When conducting cross-database queries, try to avoid using complex join methods such as cross-database joins or nested queries, and consider using simple join methods like INNER JOIN or LEFT JOIN.
3. Optimize your query by avoiding the use of many functions, subqueries, or calculations in order to reduce complexity. Split complex operations into simpler steps for better query performance.
4. Consider utilizing temporary tables or table variables: In cross-database queries, it is advisable to store the query results in temporary tables or table variables in order to reduce the frequency of cross-database queries.
5. Avoid frequent cross-database queries: Whenever possible, try to minimize the frequency of cross-database queries by storing related data in the same database.
6. Update statistical information: Regularly update the database’s statistics to ensure the query optimizer can choose the correct execution plan.
7. Adjusting server configuration: It is possible to adjust the parameters of SQL Server, such as increasing memory or adjusting cache size, in order to improve database performance.

By utilizing the methods mentioned above, the performance of cross-database queries in SQL Server can be effectively improved. If the issue persists, considering conducting performance analysis on the database to identify specific bottlenecks and optimize them.