Beginner

680. JOIN with Filtered CTE

Use a filtered CTE to prepare a smaller dataset before JOINing it with another table.

📘 Lesson 680 of 728 ⏱ 15 min 🎯 Advanced

A filtered CTE creates a named result containing only the required records before the main JOIN is performed.

Filtering early can simplify query logic and may reduce the amount of data involved in later operations.

Filter high-value orders first and then JOIN them with customer information.

SQL 
WITH HighValueOrders AS (
    SELECT
        OrderID,
        CustomerID,
        OrderAmount
    FROM Orders
    WHERE OrderAmount >= 50000
)
SELECT
    c.CustomerName,
    h.OrderID,
    h.OrderAmount
FROM Customers c
INNER JOIN HighValueOrders h
    ON c.CustomerID = h.CustomerID;

Used in financial reporting, customer analytics, dashboards, and large data-processing queries.

  • The CTE filters data before the final JOIN.
  • It makes complex queries easier to read.
  • It can reduce intermediate data.
  • The CTE should contain only required columns when practical.
  • Performance should still be verified with the execution plan.
Why filter data inside a CTE before JOINing?

It can simplify the query and reduce the rows that participate in the later JOIN.

Does a CTE automatically guarantee better performance?

No. A CTE primarily improves query organization; the optimizer determines the actual execution strategy.

Have you finished this lesson?

Introduction to SQL – All Lessons