IN and NOT IN operators in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the IN operator do in SQL?

The IN operator checks if a value matches any value in a list or subquery. It helps filter rows where a column's value is in a specified set.

beginner

How does the NOT IN operator work?

The NOT IN operator filters rows where a column's value is NOT in the specified list or subquery. It excludes those values.

beginner

Write a simple SQL query using IN to find employees in departments 1, 2, or 3.

SELECT * FROM employees WHERE department_id IN (1, 2, 3);

intermediate

What happens if the list in NOT IN contains NULL?

If the list contains NULL, NOT IN may return no rows because comparisons with NULL are unknown. It's safer to avoid NULL in NOT IN lists.

intermediate

Can IN and NOT IN be used with subqueries? Give an example.

Yes. Example: SELECT * FROM employees WHERE department_id IN (SELECT id FROM departments WHERE active = 1);

Which SQL operator checks if a value is inside a list of values?

A BETWEEN

B NOT IN

C IN

D LIKE

The IN operator checks if a value matches any value in a list.

What does NOT IN do in a SQL query?

A Includes rows with values in the list

B Excludes rows with values in the list

C Checks for NULL values only

D Sorts the results

NOT IN excludes rows where the column's value is in the specified list.

What is the result if the list in NOT IN contains NULL?

A All rows are returned

B Only rows with NULL values are returned

C It causes a syntax error

D No rows are returned

NOT IN with NULL in the list returns no rows because comparisons with NULL are unknown.

Which of these is a valid use of IN with a subquery?

A SELECT * FROM employees WHERE department_id IN (SELECT id FROM departments WHERE active = 1);

B SELECT * FROM employees WHERE department_id NOT IN (SELECT id FROM departments WHERE active = 1);

C SELECT * FROM employees WHERE department_id = IN (1, 2, 3);

D SELECT * FROM employees WHERE department_id IN 1, 2, 3;

Option A correctly uses IN with a subquery to filter employees by active departments.

Which operator would you use to find rows where a column's value is NOT in a list?

A NOT IN

B IN

C BETWEEN

D LIKE

NOT IN filters out rows where the column's value is in the list.

Explain how the IN operator works and give a simple example.

Think about filtering rows by matching values.

Describe a potential issue when using NOT IN with NULL values in the list.

Consider how SQL treats NULL in comparisons.

Practice

1. What does the IN operator do in a MySQL query?

easy

A. Checks if a value is greater than all values in a list

B. Checks if a value is less than all values in a list

C. Checks if a value matches any value in a list

D. Checks if a value is equal to a single value only

Solution

1. Step 1: Understand the purpose of IN operator

   The IN operator is used to test if a value exists within a set of values.

2. Step 2: Compare with other options

   The options describing comparisons with all values (greater or less than all) are incorrect, as IN checks if a value matches any in the list. The option about equality to a single value is also wrong, since IN handles multiple values.

3. Final Answer:

   Checks if a value matches any value in a list -> Option C

4. Quick Check:

   IN operator = check value in list [OK]

Hint: IN means "is in this list"; NOT IN means "not in this list" [OK]

Common Mistakes:

• Confusing IN with equality (=) operator
• Thinking IN checks all values instead of any
• Mixing IN with greater than or less than comparisons

2. Which of the following is the correct syntax to select rows where the column status is either 'active', 'pending', or 'closed'?

easy

A. SELECT * FROM table WHERE status IN ('active', 'pending', 'closed');

B. SELECT * FROM table WHERE status = IN ('active', 'pending', 'closed');

C. SELECT * FROM table WHERE status NOT IN ('active', 'pending', 'closed');

D. SELECT * FROM table WHERE status IN 'active', 'pending', 'closed';

Solution

1. Step 1: Check correct IN syntax

   The correct syntax uses IN followed by parentheses containing a comma-separated list of values.

2. Step 2: Identify errors in other options

   SELECT * FROM table WHERE status = IN ('active', 'pending', 'closed'); has an extra '=' which is invalid. SELECT * FROM table WHERE status NOT IN ('active', 'pending', 'closed'); uses NOT IN which selects rows not matching the list. SELECT * FROM table WHERE status IN 'active', 'pending', 'closed'; misses parentheses around the list.

3. Final Answer:

   SELECT * FROM table WHERE status IN ('active', 'pending', 'closed'); -> Option A

4. Quick Check:

   Correct IN syntax uses parentheses and no '=' [OK]

Hint: IN must be followed by parentheses with values inside [OK]

Common Mistakes:

• Using '=' before IN
• Omitting parentheses around the list
• Confusing IN with NOT IN

3. Given the table employees with a column department, what will this query return?

SELECT name FROM employees WHERE department NOT IN ('HR', 'Finance');

medium

A. Names of employees in HR or Finance departments

B. Names of employees not in HR or Finance departments

C. Names of employees only in HR department

D. Syntax error due to NOT IN usage

Solution

1. Step 1: Understand NOT IN operator

   NOT IN selects rows where the column value is not in the given list.

2. Step 2: Apply to the query context

   The query returns employee names whose department is not 'HR' or 'Finance'.

3. Final Answer:

   Names of employees not in HR or Finance departments -> Option B

4. Quick Check:

   NOT IN excludes listed values [OK]

Hint: NOT IN excludes listed values from results [OK]

Common Mistakes:

• Thinking NOT IN returns only listed values
• Confusing NOT IN with IN
• Assuming syntax error with NOT IN

4. Identify the error in this query:

SELECT * FROM orders WHERE order_status NOT IN 'shipped', 'delivered';

medium

A. Missing parentheses around the list after NOT IN

B. Incorrect use of NOT IN instead of IN

C. order_status should be in quotes

D. No error, query is correct

Solution

1. Step 1: Check syntax of NOT IN usage

   NOT IN must be followed by parentheses containing the list of values.

2. Step 2: Identify missing parentheses

   The query lists values without parentheses, causing syntax error.

3. Final Answer:

   Missing parentheses around the list after NOT IN -> Option A

4. Quick Check:

   NOT IN requires parentheses around values [OK]

Hint: Always use parentheses after IN or NOT IN [OK]

Common Mistakes:

• Omitting parentheses around value list
• Using quotes incorrectly around column names
• Confusing IN and NOT IN usage

5. You want to find customers who have placed orders but exclude those from countries 'USA', 'Canada', and 'Mexico'. Which query correctly uses NOT IN to achieve this?

hard

A. SELECT customer_id FROM orders WHERE country != ('USA', 'Canada', 'Mexico');

B. SELECT customer_id FROM orders WHERE country IN ('USA', 'Canada', 'Mexico');

C. SELECT customer_id FROM orders WHERE country NOT IN 'USA', 'Canada', 'Mexico';

D. SELECT customer_id FROM orders WHERE country NOT IN ('USA', 'Canada', 'Mexico');

Solution

1. Step 1: Understand the goal

   We want customers excluding those from USA, Canada, and Mexico.

2. Step 2: Choose correct NOT IN syntax

   SELECT customer_id FROM orders WHERE country NOT IN ('USA', 'Canada', 'Mexico'); uses NOT IN with parentheses and a list, correctly excluding those countries.

3. Step 3: Identify errors in other options

   SELECT customer_id FROM orders WHERE country IN ('USA', 'Canada', 'Mexico'); includes those countries (wrong). SELECT customer_id FROM orders WHERE country NOT IN 'USA', 'Canada', 'Mexico'; misses parentheses (syntax error). SELECT customer_id FROM orders WHERE country != ('USA', 'Canada', 'Mexico'); uses != with a list, which is invalid syntax.

4. Final Answer:

   SELECT customer_id FROM orders WHERE country NOT IN ('USA', 'Canada', 'Mexico'); -> Option D

5. Quick Check:

   NOT IN with parentheses excludes listed values [OK]

Hint: Use NOT IN with parentheses to exclude multiple values [OK]

Common Mistakes:

• Using != with multiple values
• Omitting parentheses after NOT IN
• Confusing IN and NOT IN