Is Using an Implicit SELECT within an UPDATE Statement the Optimal Approach for Combining SQL Server Inserts and Updates?

Combining Inserts and Updates in SQL Server Stored Procedures

Question:

In an effort to optimize efficiency, a stored procedure has been developed that performs an update if a record exists and inserts if it does not. The stored procedure utilizes an implicit select within an update statement to handle both scenarios. Is this an optimal approach?

Answer:

Your logic is correct, and this is a suitable approach for combining inserts and updates in a stored procedure, commonly known as UPSERT or MERGE pattern.

The rationale behind this approach is that it significantly reduces the number of database reads compared to performing separate select statements for both scenarios. By attempting an update first and only performing an insert if no rows are affected, you minimize I/O operations on the database.

Importance of UPSERT:

As highlighted in a discussion on sqlservercentral.com, UPSERT can significantly improve performance by eliminating redundant reads:

"For every update... we are removing one additional read from the table if we use the UPSERT instead of EXISTS."

This optimization is particularly beneficial when the row is likely to exist, as it eliminates an unnecessary select statement.

Considerations:

It's important to note that this pattern may not always be the best choice. In scenarios where you frequently encounter non-existent records, it may be more efficient to perform an explicit select to check for existence before attempting an update.

Additionally, as mentioned in the provided edit, there can be potential issues with this pattern related to concurrency and race conditions. It's recommended to consult additional resources to understand the best practices and potential pitfalls of using this approach.

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