Getting result of dynamic SQL into a variable for sql-server

sql

sql-injection

dynamic-sql

error-handling

byAlex Kataev·Nov 30, 2024

To execute dynamic SQL and capture the output in a variable, use sp_executesql. This system stored procedure takes SQL string and parameters, including OUTPUT:

DECLARE @SQL NVARCHAR(MAX), @Result INT, @ParamDef NVARCHAR(MAX);
SET @SQL = N'SELECT @Res = COUNT(*) FROM MyTable WHERE MyColumn = @Value;';
SET @ParamDef = N'@Res INT OUTPUT, @Value INT';
EXEC sp_executesql @SQL, @ParamDef, @Res = @Result OUTPUT, @Value = 10;
SELECT @Result; -- Holds result. How simple?

Replace MyTable, MyColumn, and @Value as suited to your query. You'll find your output hoisted aboard the good ship @Result.

Handling SQL Injection

Type-Safe parameter passing

By parameterizing dynamic SQL, you can pretend to be a superhero preventing SQL injection attacks? Because you are!

DECLARE @SQL NVARCHAR(MAX), @FieldName NVARCHAR(128), @TableName NVARCHAR(128), @Result INT;
SET @FieldName = N'MyColumn';
SET @TableName = N'MyTable';
SET @SQL = N'SELECT @Res = COUNT(*) FROM ' + QUOTENAME(@TableName) + ' WHERE ' + QUOTENAME(@FieldName) + ' = @Value';
EXEC sp_executesql @SQL, N'@Res INT OUTPUT, @Value INT', @Res = @Result OUTPUT, @Value = 10;
SELECT @Result;

Dynamic SQL - Datatypes Matter

For complex data types, ensure you match SQL data types to the ones in sp_executesql parameters. It's like, trying to fit a square peg in a round hole wouldn't work, right?

Error Handling - It's Not You, It's Them

Errors are like ex-partners, they pop up when least expected. Use TRY/CATCH blocks:

BEGIN TRY
    -- Dynamic SQL execution
END TRY
BEGIN CATCH
    -- Handle error just like dinner with your in-laws, with caution.
    SELECT ERROR_MESSAGE();
END CATCH

Optimizing? Sounds Complicated!

Avoid complexity like avoiding your boss on a Friday evening. Use execution plans to know what's cooking inside your queries.

Peeking Inside Dynamic SQL

Using EXECUTE AS - Be Someone Else!

EXECUTE AS is the SQL equivalent of walking in someone else's shoes, especially when you require specific permissions:

EXECUTE AS LOGIN = 'YourLogin';
-- Perform your magic, you wizard!
REVERT;

Null Values - Ghosts in the Machine

Ghosts or null values, both are undefined presences. Handle potential nulls with ISNULL or COALESCE:

SET @SQL = N'SELECT @Res = ISNULL(SUM(MyColumn), 0) FROM MyTable WHERE MyCondition = @Value';

Multiplying Results - It's Like a Magic Show!

To store more than one dynamic query result, use temporary tables or table variables:

DECLARE @TempTable TABLE (Column1 INT, Column2 VARCHAR(100));
INSERT INTO @TempTable EXEC sp_executesql @SQL;
-- Do multiple results feel a bit too crowded?