SQL Server MERGE Statement Tutorial

Understanding the MERGE Statement

The MERGE statement performs conditional insert, update, or delete operations on a target table by comparing it with a source table or dataset.

It requires a join condition to match rows between the source and target tables.

• Source: The dataset or table providing new or updated data.
• Target: The table to be modified based on the source data.
• ON clause: Defines how rows from source and target are matched.
• WHEN MATCHED: Defines actions for matched rows (usually UPDATE or DELETE).
• WHEN NOT MATCHED BY TARGET: Defines actions for source rows not found in target (usually INSERT).
• WHEN NOT MATCHED BY SOURCE: Defines actions for target rows not found in source (usually DELETE).

MERGE Statement Syntax

The basic syntax of the MERGE statement includes specifying the target and source tables, the matching condition, and the actions to perform based on match results.

Practical MERGE Example

Let's look at a practical example where we synchronize a target table with new data from a source table.

MERGE Statement Example Code

Here is the SQL code to perform the synchronization using MERGE: