Using Temporary Tables in SQL Server


Temporary tables in SQL Server are special tables that exist only for the duration of a database session. They are useful for storing and manipulating temporary data within a specific scope. In this guide, we'll explore the different types of temporary tables and how to use them with SQL code examples.


Types of Temporary Tables

SQL Server provides two main types of temporary tables:


  1. Local Temporary Tables: These tables are prefixed with a single pound sign (#) and are only visible to the session that creates them. They are automatically dropped when the session ends.
  2. Global Temporary Tables: These tables are prefixed with a double pound sign (##) and are visible to all sessions. They are dropped when the last session referencing them ends.

Creating Temporary Tables

Here's an example of creating a local temporary table:


-- Create a local temporary table
CREATE TABLE #LocalTempTable (
    ID INT,
    Name NVARCHAR(50)
);

And here's an example of creating a global temporary table:


-- Create a global temporary table
CREATE TABLE ##GlobalTempTable (
    ID INT,
    Description NVARCHAR(100)
);

Populating and Querying Temporary Tables

You can insert data into temporary tables and query them like regular tables. Here's an example of inserting data into a local temporary table and querying it:


-- Insert data into the local temporary table
INSERT INTO #LocalTempTable (ID, Name)
VALUES (1, 'John'), (2, 'Alice');
-- Query the local temporary table
SELECT * FROM #LocalTempTable;

Lifetime of Temporary Tables

Local temporary tables are automatically dropped when the session that created them ends. Global temporary tables are dropped when the last session referencing them ends or when explicitly dropped by a user.


Benefits of Temporary Tables

Temporary tables are useful for:


  • Storing intermediate results for complex queries.
  • Breaking down complex tasks into manageable steps.
  • Isolating data within a specific session or task.

What's Next?

You've learned how to create and use temporary tables in SQL Server. To become proficient, you can explore advanced topics such as indexing temporary tables for better performance and understanding the scope and limitations of temporary tables in various SQL Server components.


Temporary tables are valuable tools for managing and processing data within the context of your SQL Server sessions.