When not matched by source does it delete?

When not matched by source 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 can I use instead of MERGE in SQL?

Otherwise, an INSERT statement is performed. The alternative way, which you can use instead of applying the MERGE statement, is to write a sequence of INSERT, UPDATE, and DELETE statements, where, for each row, the decision is made whether to insert, delete, or update the data.

How do you MERGE tables in SQL?

Key learnings

1. use the keyword UNION to stack datasets without duplicate values.
2. use the keyword UNION ALL to stack datasets with duplicate values.
3. use the keyword INNER JOIN to join two tables together and only get the overlapping values.

Can we use DELETE in MERGE statement in Oracle?

The Merge statement was introduced in Oracle 9i and improved upon in Oracle 10g. In Oracle 9i only the INSERT and UPDATE parts were supported, in Oracle 10g DELETE was added. DELETE can only occur in the “merge_update_clause” of the above schema. This means that it must occur in the WHEN MATCHED THEN clause.

Which is faster MERGE or UPDATE?

The UPDATE statement will most likely be more efficient than a MERGE if the all you are doing is updating rows. Given the complex nature of the MERGE command’s match condition, it can result in more overhead to process the source and target rows.

How can I MERGE two tables?

You can click and drag the table using that handle. Drag the table until its top row aligns with the bottom row of the table you’re merging into. When you release your mouse button, Word merges the two tables. Now you know how to easily merge and split tables and table cells in Microsoft Word.

Is MERGE a DDL command?

This statement is a convenient way to combine multiple operations. It lets you avoid multiple INSERT , UPDATE , and DELETE DML statements. MERGE is a deterministic statement. That is, you cannot update the same row of the target table multiple times in the same MERGE statement.

What happens when merge is not matched by source?

WHEN NOT MATCHED BY TARGET always results in an INSERT. That is, this is for rows that exists in the source, but are not in the target table. WHEN NOT MATCHED BY SOURCE most often results in a DELETE, but it can also lead to an UPDATE. These are rows that exists in the target table, but which is not in the source.

When to use when not matched by source in SQL?

Only target columns and columns in the clause scope are allowed in the ‘WHEN NOT MATCHED BY SOURCE’ clause of a MERGE statement. When you want to have a condition in a MERGE with source and target for WHEN NOT MATCHED clause, you may likely to get an error message as below, if you put the condition directly to the MERGE statement.

When to delete rows in SQL Server MERGE statement?

Use below T-SQL script to create tables and insert sample data into tables. WHEN MATCHED clause in SQL Server MERGE statement is used to update, delete the rows in the target table when the rows are matched with the source table based on the join condition.

When to use the merge clause in SQL Server?

Using MERGE to update matched rows WHEN MATCHED clause in SQL Server MERGE statement is used to update, delete the rows in the target table when the rows are matched with the source table based on the join condition.