How can you improve the performance of a MERGE statement in SQL Server?

How can you improve the performance of a MERGE statement in SQL Server?

Our first task was to change the MERGE statement to meet all of the required conditions for optimization:

1. Target table’s join column has a unique or primary key constraint.
2. UPDATE and INSERT clauses include every column in the target table.
3. UPDATE and INSERT clause column attributes are identical.

Can we use where clause in MERGE statement in SQL?

The MERGE statement doesn’t have a WHERE clause. SQL Studies.

When not matched by source where does it DELETE?

We can use WHEN NOT MATCHED BY SOURCE clause in SQL Server MERGE statement to delete the rows in the target table that does not match join condition with a source table. For example, the row with locationID =2 in the target table does not match the join condition and the row is present only in the target table.

What is the purpose of MERGE in SQL Server 2008?

In SQL Server 2008, you can perform insert, update, or delete operations in a single statement using the MERGE statement. The MERGE statement allows you to join a data source with a target table or view, and then perform multiple actions against the target based on the results of that join.

Can I simplify this MERGE statement w.r.t?

The UDT Table-Type has the same design as the `dbo.Items` table. WITH existing AS — Using a CTE as the MERGE target to allow *safe* use of `WHEN NOT MATCHED BY SOURCE THEN DELETE` and apparently it’s good for performance.

Can a MERGE statement have two when matched clauses?

At most, we can specify only two WHEN MATCHED clauses in the MERGE statement. If two WHEN MATCHED clauses are specified, one clause must have an update operation and the other one must use delete operation. Please refer to below T-SQL script for the example for the MERGE statement with two WHEN MATCHED clauses.

When to use ” or ” in the merge condition?

If there are two WHEN MATCHED clauses, then one must specify an UPDATE action and one must specify a DELETE action. If UPDATE is specified in the clause, and more than one row of matches a row in target_table based on , SQL Server returns an error.

Can a MERGE statement update the same table multiple times?

A MERGE statement cannot UPDATE/DELETE the same row of the target table multiple times. Refine the ON clause to ensure a target row matches at most one source row, or use the GROUP BY clause to group the source rows.”