How to Insert into Temp Table in SQL Server

Greetings, Dev! In this article, we will discuss the concept of inserting data into temporary tables in SQL Server. This feature allows you to store and manipulate interim data efficiently, which can come in handy when dealing with complex queries or massive amounts of data.

What is a Temp Table?

Before we dive into the process of inserting data into a temp table, let’s first understand what a temp table is. A temporary table, as the name suggests, is a table that is created and exists temporarily for a specific session or query. Once the session or query ends, the temp table is automatically deleted.

Temp tables can be created using the CREATE TABLE statement, just like any other regular table. However, there are some differences in syntax and usage that we will explore further in this article.

How to Insert Data into a Temp Table in SQL Server

Now that we have a basic understanding of temporary tables, let’s move on to the process of inserting data into them. There are multiple methods to insert data into a temp table in SQL Server. We will cover the most commonly used ones below.

Method 1: SELECT INTO Statement

The SELECT INTO statement is used to create a new table and insert data from an existing table. In the case of a temp table, the new table is a temporary one that is created on the fly.

The syntax for using the SELECT INTO statement to insert data into a temp table is as follows:

Keyword	Description
SELECT	Specifies the data to be selected
INTO	Specifies that a new table is to be created
#TempTableName	Specifies the name of the new temporary table to be created
FROM	Specifies the name of the source table to select data from

Here’s an example query that demonstrates the usage of the SELECT INTO statement:

SELECT *INTO #ProductListFROM ProductsWHERE ProductID BETWEEN 1 AND 10

This query creates a new temporary table called #ProductList and inserts the data from the Products table where the ProductID is between 1 and 10.

Method 2: INSERT INTO Statement

The INSERT INTO statement is used to insert data into an existing table. However, it can also be used to insert data into a temp table, provided that the temp table has been created beforehand using the CREATE TABLE statement.

The syntax for using the INSERT INTO statement to insert data into a temporary table is similar to that of inserting data into a regular table:

Keyword	Description
INSERT INTO	Specifies the table to insert data into
#TempTableName	Specifies the name of the temporary table to insert data into
VALUES	Specifies the values to be inserted into the temporary table

Here’s an example query that demonstrates the usage of the INSERT INTO statement:

CREATE TABLE #EmployeeDetails(EmployeeID INT,EmployeeName VARCHAR(50),Salary DECIMAL(10,2))INSERT INTO #EmployeeDetails (EmployeeID, EmployeeName, Salary)VALUES (101, 'John Doe', 50000.00),(102, 'Jane Smith', 65000.00),(103, 'Bob Johnson', 45000.00)

This query creates a new temporary table called #EmployeeDetails and inserts three rows of data into it.

FAQs

1. Can I use temporary tables to improve query performance?

Yes, temporary tables can be used to improve query performance by reducing the amount of data that needs to be processed. For example, if you have a complex query that involves multiple joins and calculations, you can use a temporary table to store intermediate results and then query the temp table instead of repeating the entire calculation each time.

2. Are there any limitations to using temporary tables?

Yes, there are some limitations to using temporary tables in SQL Server. For example, temporary tables cannot be used in indexed views and cannot include computed columns. Additionally, temporary tables are only accessible within the session or query in which they were created, so they cannot be shared across multiple sessions or queries.

3. How can I drop a temporary table?

To drop a temporary table, you can use the DROP TABLE statement followed by the name of the temporary table. For example, if you have a temporary table called #MyTable, you can drop it using the following query:

DROP TABLE #MyTable

Just remember that any data stored in the temporary table will be lost once it is dropped, so make sure to backup or transfer the data to a permanent table if needed.

4. Can I use temporary tables in stored procedures and user-defined functions?

Yes, temporary tables can be used in stored procedures and user-defined functions. However, you need to be careful when using temporary tables in such scenarios because they can impact the overall performance and scalability of your application. It’s recommended to limit the use of temporary tables and ensure that they are properly optimized and cleaned up after use.

5. What is the difference between a local and a global temporary table?

A local temporary table is created with a single # sign as a prefix, while a global temporary table is created with a double ## sign as a prefix. Local temporary tables are only accessible within the session or query in which they were created, while global temporary tables are accessible across multiple sessions and queries. Global temporary tables are often used for sharing data between different queries or stored procedures.

Conclusion

Congratulations, Dev! You have now learned how to insert data into a temporary table in SQL Server using various methods. Temporary tables can be a powerful tool for managing and manipulating interim data in your applications. However, it’s important to use them wisely and ensure that they are properly optimized and cleaned up after use to avoid any negative impact on performance and scalability.