Create Temp Table From CTE

Temporary tables and Common Table Expressions (CTEs) are two powerful tools in SQL Server that allow developers to handle complex data transformations efficiently.

Combining these techniques by creating a temporary table from a CTE can provide significant advantages in terms of code organization, performance optimization, and reusability. In this article, we’ll learn about CTEs and Temporary Tables and also understand how to create a Temporary Table from a CTE using SQL in detail.

What are Common Table Expressions (CTEs)?

A CTE is a named temporary result set that is defined within a SQL statement. It exists only for the duration of the query in which it is used. CTEs are particularly useful for breaking down complex queries into more manageable pieces.

Syntax:

WITH CTE_Name AS (
    SELECT 
        column1, 
        column2
    FROM table_name
    WHERE condition
)
SELECT * 
FROM CTE_Name;
GO

What are Temporary Tables?

Temporary tables in SQL Server are tables that exist only for the duration of a database session. They are useful for storing intermediate results that need to be reused across multiple queries.

Syntax:

-- Create a temporary table
CREATE TABLE #temp_table_name (
    column1 DataType,
    column2 DataType
);

-- Insert data into the temporary table
INSERT INTO #temp_table_name
SELECT column1, column2
FROM table_name
WHERE condition;
GO

Steps to Create a Temporary Table from a CTE

• Here are the steps to create a temporary table from a CTE in SQL Server:
• Define the CTE to represent the intermediate result set.
• Create a temporary table with the desired schema.
• Insert data from the CTE into the temporary table.
• Use the temporary table for further queries within the session.

Example of Creating Temp Table From CTE in SQL Server

Suppose we have the following sales table:

Let's write a query to identify customers with total sales exceeding $1000 and store this information in a temporary table.

Query:

-- Step 1: Define the CTE
WITH TotalSales AS (
    SELECT 
        customer_id, 
        SUM(amount) AS total_amount
    FROM sales
    GROUP BY customer_id
    HAVING SUM(amount) > 1000
)

-- Step 2: Create a temporary table
CREATE TABLE #temp_high_value_customers (
    customer_id INT, 
    total_amount DECIMAL(10, 2)
);

-- Step 3: Insert data into the temporary table
INSERT INTO #temp_high_value_customers
SELECT * 
FROM TotalSales;

-- Step 4: Query the temporary table
SELECT * 
FROM #temp_high_value_customers;
GO

Output:

Explanation:

• The TotalSales CTE calculates the total sales for each customer, filtering out those with sales less than or equal to $1000.
• The data is then inserted into the temporary table #temp_high_value_customers, which is queried to produce the following result.

Conclusion

Creating a temporary table from a CTE in SQL Server combines the readability and modularity of CTEs with the reusability and performance benefits of temporary tables. By following the example in this article, you can leverage this technique to handle complex SQL Server scenarios effectively.