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674. JOIN with LEAD

Use LEAD with JOINed data to access the next related record.

📘 Lesson 674 of 728 ⏱ 15 min 🎯 Advanced

LEAD returns a value from a subsequent row within an ordered window.

It is useful for comparing current records with future events or determining the next transaction.

Show each customer's next order date.

SQL 
SELECT
    c.CustomerName,
    o.OrderDate,
    LEAD(o.OrderDate) OVER (
        PARTITION BY o.CustomerID
        ORDER BY o.OrderDate, o.OrderID
    ) AS NextOrderDate
FROM Customers c
INNER JOIN Orders o
    ON c.CustomerID = o.CustomerID;

Used in customer journeys, event analysis, scheduling, subscription analysis, and transaction timelines.

  • LEAD accesses a following row.
  • ORDER BY defines the sequence.
  • PARTITION BY keeps analysis within each customer.
  • The final row normally has NULL for the next value.
  • Useful for event-to-next-event analysis.
What does LEAD do?

LEAD returns a value from a later row in the ordered window.

Where can LEAD be useful?

It is useful for finding next transactions, next events, future dates, and gaps between activities.

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