How to use table variable in a dynamic sql statement?

sql

temp-tables

dynamic-sql

performance

byNikita Barsukov·Oct 23, 2024

In SQL, you can perform a query using a table variable within a dynamic SQL statement via sp_executesql. It enables parameter binding, which includes table variables:

DECLARE @TblVar TABLE (ID INT); // Yep, just your regular table variable
INSERT INTO @TblVar VALUES (1); // Populating it with earth-shattering value of 1

EXEC sp_executesql 
    N'SELECT * FROM @TblParam',  // Rocking it out with dynamic SQL!
    N'@TblParam TABLE(ID INT)',  // The coolest parameter you've ever seen
    @TblParam = @TblVar;         // Dial @TblParam for a good time

The @TblParam within your dynamic SQL entry corresponds to the @TblVar you initially created, which allows ample utilization in your dynamized statement!

Temporary landscapes: Table variables & Temp tables

When dealing with dynamic SQL, your temporary storage options seriously matter. While I've already shown table variables being used, there are times when temp tables may be more beneficial because they are actually acknowledged in EXEC scenarios and can offer enhanced performance.

Temp tables to the rescue!

Are you considering a switch to temp tables? Consider the following:

Scope: They're automatically discarded post-session, so management is a breeze.
Performance: Noticeably better performance for larger datasets due to improved stats and repeatability.

CREATE TABLE #TempTbl(ID INT);  // Be careful not to #TempTweet instead
INSERT INTO #TempTbl VALUES (1); // Make room for big number 1!

EXEC('SELECT * FROM #TempTbl'); // Voila! Data served fresh and hot
DROP TABLE #TempTbl;            // Au revoir, dear temp table

All about Table valued parameters (TVPs)

SQL Server 2008 onwards allows you to use TVPs to pass table data into a stored procedure. You'll be able to pass a table variable directly, however this doesn't apply for ad-hoc dynamic SQL using EXEC.

DECLARE @TblVar AS dbo.YourTableType; // Only the best type for our table
INSERT INTO @TblVar VALUES (1, 'SomeData'); // Feel the rumble of some not so random data

EXEC yourStoredProcedure @YourTableParam = @TblVar; //Trust me with this one

For this to work effectively, you need to ensure the inclusion of a defined table type in your database schema.

Scenarios where dynamic SQL wins

In some circumstances, dynamic SQL is the superior option. When it is, ensure you adhere to the following best practices:

Boil down your queries to maximize performance and minimize complexity.
Test, test and test some more to seal loopholes that can cause unforeseen errors.
Optimal use of commands such as TRUNCATE and INSERT within dynamic SQL for efficient temp table management.

Strive for better dynamic SQL

To top your dynamic SQL game, understanding its limitations and ways to overcome them is important:

Minimize table variables' limitations by opting for temp tables where dynamic SQL does not work optimally with them.
Yes, there exist subqueries: An alternate way to retrieve data sans dynamic SQL.
Give your dynamic SQL a makeover: Revamp your syntax and structure to achieve improved efficiency and precision.

Now you're well equipped to compose robust and high-performing dynamic SQL.

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