SQL Seeker

SQL Examples

SQL CTE Example

SQL Common Table Expression

Common Table Expression with CTE simplifies complex queries, including recursion.

Introduction to SQL CTE

A Common Table Expression (CTE) is a temporary result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement. CTEs simplify complex queries, improve readability, and can be recursive, providing a powerful tool for SQL developers.

Basic Syntax of CTE

The syntax for a CTE begins with the WITH keyword, followed by the CTE name and a query that defines the CTE. Here is the basic syntax:

Simple CTE Example

Let's look at a simple example of using a CTE to query a list of employees from a company database.

Advantages of Using CTEs

  • Readability: Break down complex queries into simpler parts, making them easier to understand.
  • Reusability: Use the CTE multiple times in the same query, reducing redundancy.
  • Recursion: CTEs support recursion, which is useful for hierarchical or tree-structured data.

Recursive CTE Example

Recursive CTEs are particularly useful for traversing hierarchical data, such as organizational charts. Here is an example that calculates an employee hierarchy.

When to Use CTEs

CTEs are ideal for simplifying complex queries, especially when you need to:

  • Break down a multi-step process into manageable parts.
  • Perform recursive operations on hierarchical data.
  • Improve the readability and maintainability of your SQL code.

SQL Examples

Next
Pivot Report