WHERE with AND operator in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the WHERE clause do in SQL?

The WHERE clause filters rows in a table to return only those that meet a specified condition.

beginner

How does the AND operator work in a WHERE clause?

The AND operator combines two or more conditions and returns rows only if all conditions are true.

beginner

Write a simple SQL query using WHERE with AND to find employees older than 30 and in the 'Sales' department.

SELECT * FROM employees WHERE age > 30 AND department = 'Sales';

intermediate

Can the AND operator be used with more than two conditions in a WHERE clause?

Yes, you can combine multiple conditions with AND. All must be true for a row to be included.

beginner

What happens if one condition in a WHERE clause with AND is false?

The entire WHERE condition is false, so the row is excluded from the results.

What does the AND operator do in a SQL WHERE clause?

A Returns rows where any condition is true

B Returns all rows regardless of conditions

C Returns rows where no condition is true

D Returns rows where all conditions are true

The AND operator requires all conditions to be true for a row to be included.

Which SQL query correctly uses WHERE with AND to find products priced above 100 and in stock?

A SELECT * FROM products WHERE price > 100 AND stock > 0;

B SELECT * FROM products WHERE price > 100 OR stock > 0;

C SELECT * FROM products WHERE price > 100;

D SELECT * FROM products WHERE stock > 0;

Only option A uses AND to require both conditions: price above 100 and stock available.

If a row meets the first condition but not the second in a WHERE clause with AND, will it be included?

A Yes, because one condition is true

B No, because all conditions must be true

C Yes, if the second condition is false

D No, because <code>AND</code> ignores conditions

With AND, all conditions must be true for the row to be included.

Can you use more than two conditions combined with AND in a WHERE clause?

A Only three conditions are allowed

B No, only two conditions are allowed

C Yes, any number of conditions can be combined

D Only if combined with <code>OR</code>

SQL allows combining many conditions with AND in a WHERE clause.

What is the result of this query?
SELECT * FROM users WHERE age > 18 AND city = 'Paris';

A Users older than 18 who live in Paris

B Users older than 18 or who live in Paris

C Users younger than 18 who live in Paris

D All users regardless of age or city

The query returns users who satisfy both conditions: age over 18 and city equals Paris.

Explain how the WHERE clause with the AND operator filters data in SQL.

Think about how you pick fruits that are both ripe and red.

Write an example SQL query using WHERE with AND to find records matching two conditions.

Try to find employees who work in 'HR' and have a salary above 50000.

Practice

1. What does the WHERE clause with the AND operator do in an SQL query?

easy

A. Filters rows that meet any one of the conditions

B. Joins two tables together

C. Filters rows that meet all specified conditions

D. Sorts the result set in ascending order

Solution

1. Step 1: Understand the WHERE clause

   The WHERE clause filters rows based on conditions given in the query.

2. Step 2: Understand the AND operator

   The AND operator requires all conditions to be true for a row to be included.

3. Final Answer:

   Filters rows that meet all specified conditions -> Option C

4. Quick Check:

   WHERE + AND = all conditions true [OK]

Hint: AND means all conditions must be true together [OK]

Common Mistakes:

• Thinking AND means any condition can be true
• Confusing WHERE with JOIN
• Assuming AND sorts data

2. Which of the following is the correct syntax to select rows where age is greater than 18 AND city is 'New York'?

easy

A. SELECT * FROM users WHERE age > 18 AND city = 'New York';

B. SELECT * FROM users WHERE age > 18, city = 'New York';

C. SELECT * FROM users WHERE age > 18 OR city = 'New York';

D. SELECT * FROM users WHERE age > 18 AND city == 'New York';

Solution

1. Step 1: Check the operator between conditions

   The question asks for AND, so the operator must be AND, not OR or comma.

2. Step 2: Check the comparison operators

   Use single equals (=) for comparison in SQL, not double equals (==).

3. Final Answer:

   SELECT * FROM users WHERE age > 18 AND city = 'New York'; -> Option A

4. Quick Check:

   AND + = correct syntax [OK]

Hint: Use AND and single = for conditions in WHERE [OK]

Common Mistakes:

• Using OR instead of AND
• Using comma instead of AND
• Using == instead of = for comparison

3. Given the table employees with columns name, department, and salary, what will this query return?

SELECT name FROM employees WHERE department = 'Sales' AND salary > 50000;

medium

A. Names of employees in Sales with salary over 50000

B. Names of employees in Sales or salary over 50000

C. All employees with salary over 50000

D. Syntax error due to missing OR

Solution

1. Step 1: Analyze the WHERE clause conditions

   The query filters rows where department equals 'Sales' AND salary is greater than 50000.

2. Step 2: Understand the AND effect

   Only employees meeting both conditions will be selected, so names returned are from Sales with salary above 50000.

3. Final Answer:

   Names of employees in Sales with salary over 50000 -> Option A

4. Quick Check:

   AND filters both conditions true [OK]

Hint: AND means both conditions must be true to select rows [OK]

Common Mistakes:

• Thinking OR is used instead of AND
• Assuming it returns all employees with salary > 50000
• Believing syntax error occurs without OR

4. Identify the error in this SQL query:

SELECT * FROM products WHERE price > 100 AND category 'Electronics';

medium

A. AND should be OR

B. Missing comparison operator (=) before 'Electronics'

C. price > 100 is invalid syntax

D. Missing FROM keyword

Solution

1. Step 1: Check the WHERE clause syntax

   The condition after AND is missing a comparison operator before 'Electronics'. It should be category = 'Electronics'.

2. Step 2: Verify other parts

   price > 100 is correct, AND is valid, and FROM is present.

3. Final Answer:

   Missing comparison operator (=) before 'Electronics' -> Option B

4. Quick Check:

   Comparison operator needed before value [OK]

Hint: Each condition needs a comparison operator like = [OK]

Common Mistakes:

• Omitting = in conditions
• Replacing AND with OR incorrectly
• Ignoring syntax errors in WHERE clause

5. You have a table orders with columns order_id, customer_id, status, and total. Write a query to find all orders with status 'shipped' AND total greater than 100, but exclude orders where customer_id is NULL. Which query is correct?

hard

A. SELECT * FROM orders WHERE status = 'shipped' AND total > 100 AND customer_id != NULL;

B. SELECT * FROM orders WHERE status = 'shipped' OR total > 100 AND customer_id IS NOT NULL;

C. SELECT * FROM orders WHERE status = 'shipped' AND total > 100 OR customer_id IS NOT NULL;

D. SELECT * FROM orders WHERE status = 'shipped' AND total > 100 AND customer_id IS NOT NULL;

Solution

1. Step 1: Combine conditions with AND

   We want orders where status is 'shipped' AND total is greater than 100 AND customer_id is not NULL.

2. Step 2: Use correct syntax for NULL check

   In SQL, to check for NULL, use IS NOT NULL, not != NULL.

3. Final Answer:

   SELECT * FROM orders WHERE status = 'shipped' AND total > 100 AND customer_id IS NOT NULL; -> Option D

4. Quick Check:

   Use AND and IS NOT NULL for correct filtering [OK]

Hint: Use IS NOT NULL to exclude NULLs with AND [OK]

Common Mistakes:

• Using OR instead of AND
• Using != NULL instead of IS NOT NULL
• Mixing AND and OR without parentheses