Can we use Delete in MERGE statement?

Can we use Delete in MERGE statement?

Instead of writing a subquery in the WHERE clause, you can use the MERGE statement to join rows from a source tables and a target table, and then delete from the target the rows that match the join condition.

Is MERGE faster than delete and INSERT?

The basic set-up data is as follows. We’ve purposely set up our source table so that the INSERTs it will do when merged with the target are interleaved with existing records for the first 500,000 rows. These indicate that MERGE took about 28% more CPU and 29% more elapsed time than the equivalent INSERT/UPDATE.

Does MERGE delete rows?

A single MERGE statement can also combine both DELETE and INSERT operations, or can combine both UPDATE and INSERT operations without deleting any rows. The source table is unchanged by the MERGE statement.

What is MERGE in db2?

The MERGE statement updates a target (a table or view, or the underlying tables or views of a fullselect) using data from a source (result of a table reference). Rows in the target that match the source can be deleted or updated as specified, and rows that do not exist in the target can be inserted.

How does MERGE statement work?

The MERGE statement basically works as separate INSERT, UPDATE, and DELETE statements all within the same statement. You specify a “Source” record set and a “Target” table and the JOIN condition between the two.

What is the purpose of MERGE?

Use the MERGE statement to select rows from one or more sources for update or insertion into a table or view. You can specify conditions to determine whether to update or insert into the target table or view. This statement is a convenient way to combine multiple operations.

How can MERGE performance be improved?

4 Ways to improve the performance of a SQL MERGE statement

1. Do you absolutely need MERGE?
2. Create indexes.
3. Separate filtering from matching.
4. Use query hints.
5. Read the Query Plan.

How do you speed up a merged statement?

As per Optimizing MERGE Statement Performance, the best you can do is:

1. Create an index on the join columns in the source table that is unique and covering.
2. Create a unique clustered index on the join columns in the target table.

Is merge join good?

The Merge join is the most efficient join in SQL Server. In simple terms, if you see a Merge Join, your query plan is an efficient query plan and you do not need to do many changes to improve query performances. Since the Merge Join operator uses sorted data inputs, it can use any two large datasets.