Db cursor updating in same table oracle
where_clause - You must specify the where_clause if you want Oracle to execute the update operation only if the specified condition is true.The WHERE condition can apply to either the data source or the target table.MERGE is what is known as a deterministic statement.
You can specify the DELETE where_clause to clean up data in a table while the MERGE statement is populating or updating it.
Say you would like to take transformed data and use it to update our dimension table.
In the past, we'd have accomplished this by a combination of INSERT and UPDATE statements, but starting with Oracle we've now got the Oracle MERGE command which does this in one step.
The only rows affected by the delete clause of the MERGE statement are those rows in the target table that are updated by the merge operation.
This means the DELETE WHERE condition evaluates the updated value, not the original value of the row.