SQL Server Table Variables vs. Temporary Tables - A Beginner's Comparison

SQL Server provides multiple ways to store and manipulate temporary data within your queries. Two common methods are table variables and temporary tables. In this beginner's comparison, we'll explore the differences between table variables and temporary tables, their use cases, and provide sample SQL Server code to illustrate their usage.

Table Variables

Table variables are variables with a table data type that can hold a set of rows. They are often used for small amounts of data and are automatically cleaned up when the batch or stored procedure ends. Here's how you can declare and use a table variable:

-- Declare a table variable
DECLARE @MyTableVariable TABLE (
    ID INT,
    Name VARCHAR(50)
);
-- Insert data into the table variable
INSERT INTO @MyTableVariable (ID, Name)
VALUES (1, 'John'), (2, 'Jane');
-- Query the table variable
SELECT * FROM @MyTableVariable;
    

Temporary Tables

Temporary tables are physical tables that are stored in the tempdb database. They are often used for larger datasets and can persist beyond the current batch or stored procedure. To create and use a temporary table, you can use the following code:

-- Create a temporary table
CREATE TABLE #MyTemporaryTable (
    ID INT,
    Name VARCHAR(50)
);
-- Insert data into the temporary table
INSERT INTO #MyTemporaryTable (ID, Name)
VALUES (1, 'John'), (2, 'Jane');
-- Query the temporary table
SELECT * FROM #MyTemporaryTable;
-- Don't forget to clean up the temporary table
DROP TABLE #MyTemporaryTable;
    

Key Differences

Here are some key differences between table variables and temporary tables:

• Table variables are created in memory, while temporary tables are stored in tempdb.
• Table variables are scoped to the current batch or procedure, while temporary tables can persist across batches and sessions.
• Temporary tables allow for the use of indexes and statistics, which can impact query performance.
• Table variables are generally faster for small datasets, while temporary tables may perform better for larger datasets or complex operations.

What's Next?

Understanding the differences between table variables and temporary tables is important for optimizing your SQL Server queries. The choice between them depends on the specific use case and data volume. Table variables are ideal for smaller datasets and when you need a short-lived container, while temporary tables offer more flexibility for larger datasets and complex operations.