How do I drop table variables in SQL-Server? Should I even do this?

sql

best-practices

performance

tempdb

byAnton Shumikhin·Nov 10, 2024

In SQL Server, table variables (@table) expire automatically when the function, batch, or stored procedure where they're declared ends, so no DROP command is necessary. To free up memory immediately after their last use, assign NULL:

DECLARE @MyTableVar TABLE(Id INT);
-- Query the table variable...let it live its short life
SET @MyTableVar = NULL; -- Hey presto! It's gone!

Cleanup time: When do table variables get dropped?

Table variables, taking up residence in the realm of TempDB, believe in leaving no trace behind. They get automatically cleaned up when your SQL session calls it a day:

Their lifespan is tied to stored procedures - they exit stage left as soon as the procedure does.
When declared within a batch or script, they're like "I'm outta here" at the end of the batch's execution.
Their self-cleaning nature makes manual dropping a thing of yesteryears, unlike some of their cousins, like temporary tables that seem to like clinging onto memory.

Temporary vs. table variables: Lifespan showdown

While temporary tables and table variables share a common surname, beware! They're not twins when it comes to their lifespan and scope.

Temporary tables (#tempTab) stick around until they're explicitly dropped or the session that created them ends.
Table variables (@tabVar), on the other hand, are bound to the batch, function, or stored procedure they're living in.

Knowing this family drama is crucial to maintain memory harmony and data integrity in your SQL saga.

Keep calm and optimize: Performance considerations

Dive in, but remember to tread carefully when navigating the waters of loops, data-heavy operations, or intricate batch executions:

In loops, swapping DELETE FROM @tableVariableName for a reset with NULL or a table drop attempt is like swapping dust for pure gold.
Improved performance is yours when dealing with bulky data sets: remember to clear the table variable before a redo. Unexpected results or data zombie apocalypse? No, thanks!
For those curious minds wondering about network gossip, it’s worth noting that unlike temporary tables, table variables don’t contribute to the transaction script drama, thus sparing you runtime headaches.

The golden rules: Best practices for using table variables

Though DROP TABLE @tableVariable might sound tempting, it's not on the menu. Bite into these best practices instead:

Say SET @tableVariable = NULL after the last useful access to release memory posthaste.
Clear out the table variable after each lap of a loop, making it squeaky clean for the next run.
Recognize that table variables are your allies for short-lived data storage without the overhead of transaction logging.
Understand that while they're fast and lightweight, table variables offer fewer customization options in indexing and statistics compared to temporary tables.

Knowing their turf: Scope understanding

Get intimate with the scope and life cycle of table variables:

A variable's territory is confined to the procedure, function, or batch in which it's declared.
Out of their territory, they cannot be accessed and automatically cease to exist.

By understanding its territories, you can make your table variables work hard without breaking SQL Server's sweat.

Dropping table variables: The final act

So here it is: you can't drop table variables with a DROP TABLE command. But knowing they're auto-managed by SQL Server can simplify your scripting. With their fast, lightweight nature, they're ideal for short-term data storage, especially when you want to side-step the overhead of logging that's part of the temporary tables' lifestyle.

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