SQL CTE Examples

by | Apr 20, 2023 | Blog | 0 comments

SQL CTE Examples A Common Table Expression (CTE) is a temporary result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement. Here are a few examples of how to use CTEs in SQL:

  1. Recursive SQL CTE Examples

A recursive CTE is used to traverse hierarchical data such as an organizational chart or a tree structure. Here is an example of a recursive CTE that generates a list of all employees and their managers in an organization:

WITH EmployeeHierarchy AS
(
  SELECT EmployeeID, Name, ManagerID
  FROM Employees
  WHERE ManagerID IS NULL
  UNION ALL
  SELECT e.EmployeeID, e.Name, e.ManagerID
  FROM Employees e
  JOIN EmployeeHierarchy eh ON e.ManagerID = eh.EmployeeID
)
SELECT *
FROM EmployeeHierarchy;
  1. Non-recursive SQL CTE Examples

A non-recursive CTE is used to simplify complex queries by breaking them down into smaller, more manageable parts. Here is an example of a non-recursive CTE that calculates the average price of all products in a certain category:

WITH CategoryProducts AS
(
  SELECT ProductID, ProductName, CategoryID, Price
  FROM Products
  WHERE CategoryID = 1
)
SELECT AVG(Price) AS AveragePrice
FROM CategoryProducts;
  1. CTE with multiple queries

You can use a CTE to simplify queries that involve multiple subqueries. Here is an example of a CTE that calculates the total sales for each employee in a certain department:

WITH EmployeeSales AS
(
  SELECT EmployeeID, SUM(SalesAmount) AS TotalSales
  FROM Sales
  WHERE DepartmentID = 2
  GROUP BY EmployeeID
)
SELECT e.EmployeeName, es.TotalSales
FROM Employees e
JOIN EmployeeSales es ON e.EmployeeID = es.EmployeeID;

These are just a few examples of how you can use CTEs in SQL to simplify complex queries and improve performance.

Common Table Expression (CTEs) are a powerful tool for creating complex queries that are easier to read and maintain. They can be used for a wide range of tasks, from retrieving hierarchical data to filtering and ranking result sets. By mastering the use of CTEs, SQL developers can create more efficient and effective queries that provide better insights into their data.

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