Understanding Temporary Tables in SQL Server

Hello Dev, welcome to this article on temporary tables in SQL Server. Temporary tables are a valuable resource in SQL Server that can help you manage large data sets effectively. In this article, we will explore the various aspects of temporary tables in SQL Server and how you can use them to your advantage. Let’s get started!

What are Temporary Tables?

In SQL Server, temporary tables are a special type of table that is used to store data temporarily. These tables are created in the TempDB database and are automatically dropped when the session ends or when the connection is closed. Temporary tables can be used to store intermediate results, perform complex calculations or to create a staging area for data manipulation.

Temporary tables are different from permanent tables in the sense that they do not exist beyond the scope of a database session. This means that you can create temporary tables without worrying about conflicting table names or data integrity issues.

How to Create a Temporary Table?

Creating a temporary table in SQL Server is simple. You need to follow the syntax:

CREATE TABLE #TempTable	(	ColumnName DataType,	ColumnName DataType,	ColumnName DataType	)

Here, the ‘#’ sign before the table name indicates that this is a temporary table. You can also create a local temporary table by using a double hash (##) before the table name. The difference between a local temporary table and a global temporary table is that the local temporary table is visible only within the current session, while the global temporary table is visible across multiple sessions.

Example

Here’s an example of how to create a temporary table:

CREATE TABLE #Sales(ID int,SaleAmount money,SaleDate date)

This creates a temporary table named “Sales” with columns for ID, SaleAmount and SaleDate.

How to Insert Data into a Temporary Table?

Once you have created a temporary table, you can insert data into it just like a regular table. You can use the INSERT INTO statement to insert data into the temporary table.

Example

Here’s an example that inserts some data into the temporary table:

INSERT INTO #Sales (ID, SaleAmount, SaleDate)VALUES (1, 100.00, '2020-01-01'),(2, 200.00, '2020-01-02'),(3, 300.00, '2020-01-03')

This inserts three rows of data into the temporary table “Sales”.

How to Retrieve Data from a Temporary Table?

Retrieving data from a temporary table is similar to retrieving data from a regular table. You can use the SELECT statement to retrieve data from the temporary table.

Example

Here’s an example that selects data from the temporary table:

SELECT ID, SaleAmount, SaleDateFROM #Sales

This selects all the rows from the temporary table “Sales” and displays the columns ID, SaleAmount and SaleDate.

How to Drop a Temporary Table?

Temporary tables are dropped automatically when the session ends. However, if you want to drop a temporary table manually, you can use the DROP TABLE statement.

Example

Here’s an example that drops the temporary table “Sales”:

DROP TABLE #Sales

This drops the temporary table “Sales” from the database.

Advantages of Using Temporary Tables

Temporary tables offer several advantages in SQL Server:

• They provide a staging area for intermediate results.
• They allow you to manipulate data in a temporary environment, without affecting the original data set.
• They can be used to simplify complex queries and calculations.
• They can improve query performance and reduce resource usage.

FAQ

What is the difference between temporary tables and table variables?

Temporary tables and table variables are both used to store data temporarily. However, there are some differences between the two:

• Temporary tables are created in the TempDB database, while table variables are created in memory.
• Temporary tables can be indexed and have statistics, while table variables cannot be indexed.
• Temporary tables can be used in stored procedures and functions, while table variables cannot be used in functions.
• Temporary tables are dropped automatically at the end of the session, while table variables are dropped when the batch or stored procedure ends.

Can I index a temporary table?

Yes, you can index a temporary table just like a regular table. Indexing can improve the performance of queries that use the temporary table.

Can I create a temporary table in a stored procedure?

Yes, you can create a temporary table in a stored procedure. Temporary tables are scoped to the session, which means that they can be accessed by any code within the same session, including stored procedures.

Can I create a temporary table with a SELECT INTO statement?

Yes, you can create a temporary table with a SELECT INTO statement. This statement creates a new table and inserts the selected data into it.

What is the maximum size of a temporary table?

The maximum size of a temporary table is determined by the available disk space in the TempDB database.

Conclusion

Temporary tables are a powerful tool in SQL Server that can help you manage large data sets effectively. They provide a temporary storage area for intermediate results, calculations, and data manipulation. By using temporary tables, you can simplify complex queries, improve performance and reduce resource usage. Hopefully, this article has helped you understand temporary tables in SQL Server and how you can use them to your advantage.