LEAD function for next row access in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the LEAD function do in SQL?

The LEAD function lets you look at the value in the next row of a result set without moving the cursor. It helps compare current row data with the next row's data.

beginner

Write the basic syntax of the LEAD function.

LEAD(column_name, offset, default_value) OVER (PARTITION BY partition_column ORDER BY order_column)

beginner

What happens if the LEAD function tries to access a row beyond the last row?

If there is no next row, LEAD returns NULL or the default value you provide.

intermediate

Why do we use the OVER clause with LEAD?

The OVER clause defines how to group (partition) and order rows so LEAD knows which row is next.

beginner

Give a real-life example where LEAD can be useful.

LEAD can help find the next day's sales for each product to compare if sales increased or decreased.

What does LEAD(column, 1) return?

A Value from the current row in the column

B Value from the previous row in the column

C Value from the next row in the column

D Sum of all values in the column

LEAD with offset 1 returns the value from the next row in the specified column.

What will LEAD(column, 2, 0) return if there is no second next row?

A 0

B Error

C Value from the current row

D NULL

The third parameter is the default value returned if the next row does not exist. Here it is 0.

Which clause is mandatory to use LEAD function properly?

A WHERE

B GROUP BY

C HAVING

D ORDER BY inside OVER()

LEAD requires an ORDER BY clause inside the OVER() to define the row order.

Can LEAD be used without PARTITION BY?

A No, PARTITION BY is mandatory

B Yes, it works on the entire result set

C Only with GROUP BY

D Only with HAVING

PARTITION BY is optional. Without it, LEAD works on the entire ordered result set.

What type of SQL function is LEAD?

A Window function

B Aggregate function

C Scalar function

D String function

LEAD is a window function that accesses data from another row in the result set.

Explain how the LEAD function works and why it is useful.

Think about looking ahead in a list of rows.

Describe a scenario where you would use LEAD in a sales report.

Imagine checking if sales went up or down the next day.