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.
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.
What is the need of MERGE statement?
MERGE statement improves the performance as all the data is read and processed only once whereas in previous versions three different statements have to be written to process three different activities (INSERT, UPDATE or DELETE) in which case the data in both the source and target tables are evaluated and processed …
What does not matched by source mean?
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.
What is MERGE query?
A merge query creates a new query from two existing queries. One query result contains all columns from a primary table, with one column serving as a single column containing a relationship to a secondary table. The related table contains all rows that match each row from a primary table based on a common column value.
Why does delete not match when not matched by source?
The problem I had was that the MERGE statement WHEN NOT MATCHED BY SOURCE THEN DELETE would delete everything in the TARGET table; not just the extra items no longer in the SOURCE! I could not qualify the WHEN NOT MATCHED BY SOURCE statement so that the DELETE would only affect the same invoice number in the TARGET that was no longer in the SOURCE.
When to use update delete or merge in SQL?
So, no big deal to write a sql statement that handles changes in the source table and moves them to a target table. Even removing rows from target, when they are logically deleted in the source should not be a problem as there is an update delete clause in the merge command.
What does when not matched by source mean in SQL?
I could not qualify the WHEN NOT MATCHED BY SOURCE statement so that the DELETE would only affect the same invoice number in the TARGET that was no longer in the SOURCE. An error told me “Only target columns are allowed in the ‘WHEN NOT MATCHED BY SOURCE’ clause of a MERGE statement.”
What does delete where do in merge function?
Specify the DELETE where_clause to clean up data in a table while populating or updating it. The only rows affected by this clause are those rows in the destination table that are updated by the merge operation. The DELETE WHERE condition evaluates the updated value, not the original value that was evaluated by the UPDATE SET …
