The sp_executesql is a built-in stored procedure in SQL Server that enables the execution of dynamically constructed SQL statements or batches. This procedure is a useful tool for overcoming various issues in SQL programming, such as determining displayed columns in reports. In this article, we will explore the syntax, usage, and advantages of sp_executesql.

Syntax

The syntax for sp_executesql is as follows:

sp_executesql @stmt, N'@parametername1_datatype,@parametername2_datatype,@parameternameN_datatype', @parametername1 = 'Value1', @parametername2 = 'Value2', @parameternameN = 'ValueN'

The @stmt parameter specifies the dynamically generated SQL statement or batch. The data type of this parameter must be Unicode strings, so we need to add the N prefix or use nvarchar or nchar data typed variables. The @parameternameN_datatype defines the parameter’s name and data type used in the dynamically constructed SQL statements. We can assign values to these parameters using the @parameternameN=’ValueN’ expression.

Example

Let’s consider an example where we retrieve data from the Person table in the AdventureWorks database. We want to display specific columns and filter the data based on the PersonType column.

DECLARE @SqlStatement AS NVARCHAR(1000)
DECLARE @ColNames AS NVARCHAR(100)
SET @ColNames = N'FirstName, MiddleName, LastName';
SET @SqlStatement = 'SELECT ' + @ColNames + ' FROM Person.Person WHERE PersonType=@PerType'
EXECUTE sp_executesql @SqlStatement, N'@PerType nchar(2)', @PerType = 'EM'

In this example, we assign the dynamically constructed SQL statement to the @SqlStatement variable. The @ColNames variable specifies the column names to be displayed in the result set. We filter the data based on the @PerType parameter, which has a data type of nchar(2) and filters the data where the PersonType column equals “EM”. The query is then executed, and the result set will only include the specified columns.

Using OUTPUT Parameter

sp_executesql also allows us to return the execution result of the dynamically constructed SQL statement or batch using the OUTPUT parameter. Let’s consider an example where we count the number of rows in the PersonPhone table and assign the result to a variable:

DECLARE @SqlStatement AS NVARCHAR(1000)
DECLARE @PhoneIdType AS INT
DECLARE @Result AS INT
SET @SqlStatement = 'SELECT @RowNumber=COUNT(PhoneNumber) FROM Person.PersonPhone WHERE PhoneNumberTypeID=@PhoneType'
SET @PhoneIdType = 1
EXEC sp_executesql @SqlStatement, N'@PhoneType INT, @RowNumber INT OUTPUT', @PhoneType = @PhoneIdType, @RowNumber = @Result OUTPUT
SELECT @Result AS [TableRowNumber]

In this example, we indicate the @RowNumber parameter as an OUTPUT parameter and assign its value to the @Result parameter. This allows us to retrieve the row count from the dynamically constructed query.

sp_executesql vs EXEC Statement

The EXEC statement is another option for executing dynamic SQL statements. However, sp_executesql has some advantages over the EXEC statement:

• sp_executesql has the ability to reuse cached query plans, which helps to reduce query compilation costs.
• sp_executesql allows for generating parameterized dynamic queries, making it more secure against SQL injection attacks.

On the other hand, the EXEC statement does not support parameterization and can create new query plans for each execution, potentially consuming more resources and causing performance issues.

Conclusion

In this article, we explored the sp_executesql procedure in SQL Server. We learned about its syntax, usage, and advantages over the EXEC statement. sp_executesql is a powerful tool for executing dynamically constructed SQL statements or batches, and it offers benefits such as query plan reuse and protection against SQL injection attacks. Understanding and utilizing sp_executesql effectively can greatly enhance SQL programming capabilities.