Inserting Query Results into Temporary Tables

Temporary tables are a powerful feature in SQL databases that allow you to store and manipulate data temporarily during the execution of a query or session. In this tutorial, we will explore how to insert query results into temporary tables.

Introduction to Temporary Tables

A temporary table is a database table that is created at runtime and automatically deleted when it is no longer needed. Temporary tables are useful for storing intermediate results, performing complex calculations, or simplifying queries.

There are two types of temporary tables:

• Local Temporary Tables: These tables are prefixed with a number sign (#) and are visible only to the current session.
• Global Temporary Tables: These tables are prefixed with two number signs (##) and are visible to all sessions.

Creating a Temporary Table

To create a temporary table, you can use the SELECT INTO statement. This statement creates a new table and populates it with the results of a query.

SELECT *
INTO #TempTableName
FROM YourTable;

This will create a new local temporary table named #TempTableName with the same structure as YourTable.

Inserting Query Results into a Temporary Table

To insert query results into a temporary table, you can use the following syntax:

SELECT *
INTO #TempTableName
FROM (
    -- Your query here
) AS TableName;

For example:

SELECT *
INTO #TempResults
FROM (
    SELECT Received,
           Total,
           Answer,
           (CASE WHEN application LIKE '%STUFF%' THEN 'MORESTUFF' END) AS application
    FROM FirstTable
    WHERE Recieved = 1 AND application = 'MORESTUFF'
    GROUP BY CASE WHEN application LIKE '%STUFF%' THEN 'MORESTUFF' END
) AS Data;

This will create a new local temporary table named #TempResults and populate it with the results of the query.

Dropping Temporary Tables

When you are finished using a temporary table, you should drop it to free up system resources. You can use the following syntax:

DROP TABLE #TempTableName;

It’s also a good practice to check if the temporary table exists before dropping it to avoid errors:

IF OBJECT_ID('tempdb..#TempTableName') IS NOT NULL
BEGIN
    DROP TABLE #TempTableName;
END

Best Practices

Here are some best practices to keep in mind when using temporary tables:

• Always drop temporary tables when you are finished using them.
• Use meaningful names for your temporary tables to avoid confusion.
• Avoid using global temporary tables unless necessary, as they can be visible to all sessions and may cause conflicts.

Example Use Case

Here is an example use case that demonstrates how to insert query results into a temporary table:

-- Create a sample table
CREATE TABLE FirstTable (
    Received INT,
    Total INT,
    Answer VARCHAR(50),
    application VARCHAR(50)
);

-- Insert some data into the sample table
INSERT INTO FirstTable (Received, Total, Answer, application)
VALUES (1, 10, 'Yes', 'MORESTUFF'),
       (2, 20, 'No', 'OTHERSTUFF'),
       (3, 30, 'Yes', 'MORESTUFF');

-- Create a temporary table and populate it with query results
IF OBJECT_ID('tempdb..#TempResults') IS NOT NULL
BEGIN
    DROP TABLE #TempResults;
END

SELECT *
INTO #TempResults
FROM (
    SELECT Received,
           Total,
           Answer,
           (CASE WHEN application LIKE '%STUFF%' THEN 'MORESTUFF' END) AS application
    FROM FirstTable
    WHERE Recieved = 1 AND application = 'MORESTUFF'
    GROUP BY CASE WHEN application LIKE '%STUFF%' THEN 'MORESTUFF' END
) AS Data;

-- Query the temporary table
SELECT * FROM #TempResults;

-- Drop the temporary table when finished
DROP TABLE #TempResults;

This example creates a sample table, inserts some data into it, creates a temporary table and populates it with query results, queries the temporary table, and finally drops the temporary table when finished.