SQL MERGE STATEMENT is the combination of  INSERT,  UPDATE, and  DELETE statements. Merge Statement can perform all these operations in our main target table when the source table is provided. MERGE is very useful when it comes to loading the data warehouse tables, which can be very large and require the specific actions to be taken when the rows are or are not present.

SQL Merge Statement

See the following syntax.

MERGE <target_table> [AS TARGET]
USING <table_source> [AS SOURCE]
ON <search_condition>
[WHEN MATCHED 
THEN <merge_matched> ]
[WHEN NOT MATCHED [BY TARGET]
THEN <merge_not_matched> ]
[WHEN NOT MATCHED BY SOURCE
THEN <merge_matched> ];

#How to use SQL MERGE STATEMENT

1. Identify the target table which is going to be used in that logic.
2. The next step is to identify the source table which we can use in the logic.
3. The next step is to determine the appropriate search conditions in the ON clause to match the rows.
4. Implement logic when records are matched or not matched between the target and source.
5. For each of these comparisons, conditions write the logic, and When matched, generally an update condition is used and When not matched, then insert or delete statement is used.

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