UPDATE with subquery preview in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the SQL UPDATE statement do?

The UPDATE statement changes existing data in a table by modifying one or more columns for rows that meet a condition.

beginner

What is a subquery in SQL?

A subquery is a query nested inside another query. It runs first and its result is used by the outer query.

intermediate

How can a subquery be used in an UPDATE statement?

A subquery can provide values to update columns or specify which rows to update based on data from another table.

intermediate

Example: What does this SQL do?

UPDATE employees SET salary = (SELECT AVG(salary) FROM employees) WHERE department = 'Sales';

It sets the salary of all employees in the Sales department to the average salary of all employees.

beginner

Why previewing a subquery before running an UPDATE is helpful?

Previewing lets you see the data the subquery returns, so you can avoid mistakes and update only the intended rows with correct values.

What does the subquery in an UPDATE statement do?

A Provides values or conditions for the update

B Deletes rows from the table

C Creates a new table

D Changes the table structure

The subquery provides values or conditions used to update rows in the main table.

Which SQL keyword is used to change data in existing rows?

A SELECT

B INSERT

C UPDATE

D DELETE

UPDATE modifies existing rows in a table.

What will this query do?

UPDATE products SET price = price * 1.1 WHERE category = 'Books';

A Add new books with price 1.1

B Delete all books

C Set price to 1.1 for books

D Increase price by 10% for all books

It increases the price by 10% for products in the Books category.

Why should you run a subquery alone before using it in UPDATE?

A To create a new table

B To check the data it returns

C To delete data

D To change table structure

Running the subquery alone helps verify it returns the correct data for the update.

Which clause specifies which rows to update in an UPDATE statement?

A WHERE

B FROM

C GROUP BY

D ORDER BY

The WHERE clause filters rows to update.

Explain how to use a subquery inside an UPDATE statement and why it is useful.

Think about how you can get data from one place to update another.

Describe the steps you take before running an UPDATE with a subquery to ensure it works correctly.

Preview and verify before changing data.