Efficiently Inserting Stored Procedure Results into Temporary Tables in SQL Server

Introduction

In SQL Server, temporary tables are powerful tools used to store intermediate results during complex query processing or when handling large datasets that require multiple steps. A common scenario is inserting the result set of a stored procedure directly into a temporary table without explicitly defining the columns beforehand. This tutorial will guide you through various methods to achieve this efficiently and effectively.

Understanding Stored Procedures

Stored procedures are precompiled collections of SQL statements that can accept parameters, return results, and perform complex operations on database data. They help improve performance by reducing network traffic and simplifying client applications. However, when it comes to inserting their results directly into a temporary table without specifying columns, certain techniques must be employed.

Method 1: Using INSERT INTO ... EXEC

The most straightforward method for storing the result of a stored procedure in a temporary table is using the INSERT INTO ... EXEC pattern. This approach doesn’t require you to define the structure of your temporary table beforehand as it dynamically adapts to the structure returned by the stored procedure.

Example

CREATE PROCEDURE spGetBusinessLineHistory
AS
BEGIN
    SELECT BusinessID, LineName FROM BusinessLineHistory;
END;

-- Create a temporary table with an initial structure (if necessary)
CREATE TABLE #tmpBusLine (BusinessID INT, LineName NVARCHAR(100));

-- Insert stored procedure results into the temporary table
INSERT INTO #tmpBusLine
EXEC spGetBusinessLineHistory;

SELECT * FROM #tmpBusLine;

Method 2: Inline Table-Valued Functions

If your requirement allows for flexibility between stored procedures and functions, consider using inline table-valued functions. These user-defined functions return a table that can be used directly in queries or inserted into another table.

Example

CREATE FUNCTION fnGetBusinessLineHistory(@Date DATE)
RETURNS TABLE 
AS
RETURN (
    SELECT BusinessID, LineName FROM BusinessLineHistory WHERE Date = @Date
);

-- Use the function to insert data into a temporary table
SELECT * INTO #tmpBusLineFromFunction
FROM fnGetBusinessLineHistory('2023-03-16');

Method 3: Using OPENROWSET for Ad Hoc Queries

For scenarios requiring flexibility or when working with remote servers, OPENROWSET can be used. This method involves enabling ad hoc distributed queries and might have additional security implications.

Prerequisites

sp_configure 'Show Advanced Options', 1;
RECONFIGURE;
sp_configure 'Ad Hoc Distributed Queries', 1;
RECONFIGURE;

Example

SELECT *
INTO #tmpBusLineWithOpenRowset
FROM OPENROWSET('SQLNCLI', 
                'Server=(local);Trusted_Connection=yes;',
                'EXEC spGetBusinessLineHistory');
                
SELECT * FROM #tmpBusLineWithOpenRowset;

Best Practices and Considerations

1. Security: Be cautious with OPENROWSET as it requires enabling ad hoc distributed queries, which can pose security risks.
2. Performance: Using functions like inline table-valued functions is generally more efficient than OPENROWSET due to reduced overhead.
3. Maintainability: Prefer using stored procedures or functions that encapsulate logic and make your SQL scripts easier to maintain.

Conclusion

By leveraging different approaches such as INSERT INTO ... EXEC, inline table-valued functions, and OPENROWSET, you can dynamically insert the results of a stored procedure into a temporary table without predefined columns. Choose the method best suited to your requirements while considering performance, security, and maintainability.