Understanding DB2®: Learning Visually with Examples

9.4. The MERGE Statement

A MERGE statement combines an INSERT statement with an UPDATE or DELETE statement. For example, if a row in table T1 also exists in table T2, the existing row in T2 should be updated. If a row in T1 does not exist in T2, it should be inserted into T2. A new and efficient way to code this logic can be implemented with one statement: the MERGE statement. Figure 9.25 shows this MERGE statement.

Figure 9.25. Example of a MERGE statement

MERGE INTO T2 as target USING (SELECT ... FROM T1) AS source ON target.id=source.id WHEN NOT MATCHED THEN INSERT INTO T2 ... WHEN MATCHED THEN UPDATE T2 SET ...

Figure 9.26 illustrates the syntax of a MERGE statement. The MERGE statement has a lot of intricate details; see the DB2 UDB SQL ...