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MERGE Statement

The MERGE statement is used to perform insert, update, or delete operations on a target table based on the results of a join with a source table. It is useful for synchronizing tables.

Examples of Using MERGE

Scenario: Synchronizing Two Tables

MERGE INTO FreedomFighters AS target
USING UpdatedFighters AS source
ON target.FighterID = source.FighterID
WHEN MATCHED THEN
    UPDATE SET target.Name = source.Name,
               target.City = source.City
WHEN NOT MATCHED THEN
    INSERT (FighterID, Name, City)
    VALUES (source.FighterID, source.Name, source.City);

Output:

Records synchronized between FreedomFighters and UpdatedFighters tables.

Do's and Don'ts

Do's

  • Use MERGE for complex data synchronization tasks.
  • Ensure that the join condition is accurate to avoid data discrepancies.
  • Test the MERGE statement on a subset of data before applying it to the full dataset.

Don'ts

  • Don't use MERGE without understanding its impact on data integrity.
  • Don't ignore the performance implications of merging large datasets.
  • Don't run MERGE statements without a proper backup in place.
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