Creating a Temporary Table from a Stored Procedure in SQL Server

Problem Statement:

In SQL Server, it's a common requirement to create a temporary table from the result set of a stored procedure. However, doing this is not as straightforward as it might seem. This blog will address the problem of creating a temporary table from a stored procedure's output and explain the challenges you might face.

Source of Error:

The source of the error lies in the fact that stored procedures return result sets, not tables, making it challenging to directly insert their output into a temporary table. Attempting to do so will result in syntax errors and data type mismatches.

Creating Dummy Data Sets and Performing the Operation:

Let's start by creating a simplified example to demonstrate the problem. Assume we have a stored procedure that returns a result set of employees' names and their salaries. We want to insert this data into a temporary table.

Here's a sample stored procedure:

```sql

CREATE PROCEDURE GetEmployeeSalaries AS

BEGIN

SELECT FirstName, LastName, Salary

FROM Employees;

END;

```

To create a temporary table and insert data from the stored procedure, you might initially try the following:

```sql

-- This will not work!

CREATE TABLE #TempEmployeeSalaries (

FirstName NVARCHAR(50),

LastName NVARCHAR(50),

Salary INT

);

INSERT INTO #TempEmployeeSalaries

EXEC GetEmployeeSalaries;

```

However, attempting to execute this code will result in an error.

The Solution:

The correct approach to create a temporary table from a stored procedure's result set involves using a table variable or a real temporary table (denoted by `##`) with a combination of `INSERT INTO...EXEC` statements.

Here's a modified example:

```sql

-- Create a real temporary table

CREATE TABLE ##TempEmployeeSalaries (

FirstName NVARCHAR(50),

LastName NVARCHAR(50),

Salary INT

);

-- Insert data from the stored procedure into the temporary table

INSERT INTO ##TempEmployeeSalaries

EXEC GetEmployeeSalaries;

-- Query the temporary table

SELECT * FROM ##TempEmployeeSalaries;

-- Drop the temporary table when done

DROP TABLE ##TempEmployeeSalaries;

```

Source of the Function:

The source of this solution lies in the fact that temporary tables, whether table variables or real temporary tables, can be used to store and manipulate data within a specific session. Using the `INSERT INTO...EXEC` statement, we can populate a temporary table with the result set of a stored procedure.

Advantages and Disadvantages:

Advantages:

1. Temporary tables allow you to store and work with result sets from stored procedures.

2. They help improve query performance as you can index and optimize temporary tables.

3. Temporary tables are limited to the current session, reducing the risk of data interference.

Disadvantages:

1. Temporary tables can consume resources, and creating and dropping them might impact system performance if not managed properly.

2. Using temporary tables can lead to increased complexity in your SQL code.

In conclusion, creating a temporary table from the output of a stored procedure is a useful technique in SQL Server, but it requires careful consideration and understanding of temporary table types and their scoping. By following the correct approach, you can effectively work with stored procedure result sets in temporary tables.

Vijay Kashyap
 Learn SQL in simplied way