The MERGE statement allows for a target table to be updated using the specified input data. It basically combines the functionality of an INSERT statement and an UPDATE statement into a single statement. The MERGE statement is issued with a search condition, which is usually searching on a key value. If a match is found, then the target row is updated with the specified input data. If a match is not found, then a new row is inserted into the target table with the specified input data.
This can simplify traditional processing in which an application program will execute a SELECT statement to determine the existence of a target row in a table. If the row is found, then the application program will execute an UPDATE statement to update the row; otherwise, the application program will execute an INSERT statement to add a new row to the table. The MERGE statement will now combine these three separate statements into a single SQL operation.
The MERGE statement is also enabled for multi-row processing, similar to multi-row fetch and multi-row insert processing.
