SQL Mastery: 100 Use Cases for Common Table Expression (CTE)

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Common Table Expressions (CTEs) are beneficial in various scenarios where you need to simplify and organize complex SQL queries. These scenarios showcase the versatility of CTEs in addressing various aspects of data manipulation, analysis, and query optimization in SQL. Using CTEs wisely can lead to more readable, modular, and efficient SQL code.

1. Recursive Queries:

• When dealing with hierarchical or tree-structured data, such as organizational charts or file systems, recursive CTEs are essential. They allow you to traverse and query hierarchical structures easily.

WITH RecursiveCTE (ID, ParentID, Name) AS (
    SELECT ID, ParentID, Name FROM YourTable WHERE ParentID IS NULL
    UNION ALL
    SELECT t.ID, t.ParentID, t.Name FROM YourTable t
    JOIN RecursiveCTE r ON t.ParentID = r.ID
)
SELECT * FROM RecursiveCTE;

2. Data Transformation:

• CTEs are useful for transforming data within a query, especially when dealing with multiple steps of data processing. This can include tasks like pivoting, unpivoting, or aggregating data.

WITH TransformedData AS (
    SELECT column1, column2 FROM YourTable WHERE condition
)
SELECT AVG(column1), SUM(column2) FROM TransformedData;