WHERE with IN list in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the SQL WHERE ... IN clause do?

It filters rows to include only those where a column's value matches any value in a specified list.

beginner

Write a simple example of a WHERE ... IN clause.

SELECT * FROM employees WHERE department IN ('Sales', 'Marketing');
This returns employees in either Sales or Marketing departments.

intermediate

Can the IN list contain numbers and strings together?

No, the list should contain values of the same data type as the column being filtered.

beginner

How is WHERE ... IN different from multiple OR conditions?

WHERE column IN (a, b, c) is a shorter, clearer way to write WHERE column = a OR column = b OR column = c.

intermediate

What happens if the IN list is empty?

The query returns no rows because no value can match an empty list.

What does this SQL do?
SELECT * FROM products WHERE category IN ('Books', 'Toys');

A Selects all products except Books and Toys

B Selects products not in Books or Toys categories

C Selects products with category NULL

D Selects products only in Books or Toys categories

The IN clause filters rows to those where category is either 'Books' or 'Toys'.

Which is equivalent to WHERE id IN (1, 2, 3)?

A WHERE id = 1 AND id = 2 AND id = 3

B WHERE id NOT IN (1, 2, 3)

C WHERE id = 1 OR id = 2 OR id = 3

D WHERE id > 1 AND id < 3

IN with multiple values is like OR conditions for equality.

What data type should the values in the IN list match?

A The same data type as the column

B Any data type

C Only strings

D Only numbers

Values in the IN list must match the column's data type for correct filtering.

What result do you get if the IN list is empty?

A No rows returned

B All rows returned

C Error in SQL syntax

D Returns NULL values only

An empty IN list matches no values, so no rows are returned.

Which is a benefit of using WHERE ... IN over multiple OR conditions?

A It runs slower

B It is easier to read and write

C It only works with numbers

D It returns more rows

IN makes queries shorter and clearer compared to many OR conditions.

Explain how the WHERE ... IN clause works in SQL and give a simple example.

Think about choosing items from a list.

Describe the difference between using WHERE ... IN and multiple OR conditions.

Consider how you write the conditions.

Practice

1. What does the SQL clause WHERE column_name IN (value1, value2, value3) do?

easy

A. It selects rows where column_name matches any value in the list.

B. It updates rows with values in the list.

C. It deletes rows not matching the list.

D. It creates a new table with listed values.

Solution

1. Step 1: Understand the IN clause purpose

   The IN clause checks if a column's value matches any value inside the parentheses list.

2. Step 2: Identify the effect on row selection

   Rows with the column value equal to any listed value are selected; others are ignored.

3. Final Answer:

   It selects rows where column_name matches any value in the list. -> Option A

4. Quick Check:

   WHERE with IN filters rows by listed values [OK]

Hint: IN checks if value matches any in the list [OK]

Common Mistakes:

• Thinking IN updates or deletes rows
• Confusing IN with creating tables
• Assuming IN matches all values at once

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

easy

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

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

C. SELECT * FROM orders WHERE status IN 'active', 'pending', 'closed';

D. SELECT * FROM orders WHERE status IN ('active' 'pending' 'closed');

Solution

1. Step 1: Check correct use of IN syntax

   The correct syntax is column_name IN (value1, value2, ...) without an equals sign.

2. Step 2: Identify correct punctuation and parentheses

   Values must be inside parentheses and separated by commas.

3. Final Answer:

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

4. Quick Check:

   IN syntax = column IN (values) [OK]

Hint: No '=' before IN; use commas inside parentheses [OK]

Common Mistakes:

• Using '=' before IN
• Missing commas between values
• Omitting parentheses around values

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

SELECT * FROM employees WHERE department IN ('HR', 'Sales');

medium

A. Rows where department is 'HR' or 'Sales'.

B. Rows where department is 'HR' only.

C. Rows where department is not 'HR' or 'Sales'.

D. All rows regardless of department.

Solution

1. Step 1: Understand the IN filter on department

   The query filters rows where department matches any value in ('HR', 'Sales').

2. Step 2: Determine which rows match

   Only rows with department 'HR' or 'Sales' are returned; others are excluded.

3. Final Answer:

   Rows where department is 'HR' or 'Sales'. -> Option A

4. Quick Check:

   IN filters rows matching listed values [OK]

Hint: IN returns rows matching any listed value [OK]

Common Mistakes:

• Thinking it returns rows not in the list
• Assuming it returns only one value
• Confusing IN with NOT IN

4. Identify the error in this SQL query:

SELECT * FROM products WHERE category IN 'Electronics', 'Toys', 'Books';

medium

A. Incorrect table name.

B. Using IN instead of = operator.

C. Missing parentheses around the list of values.

D. Missing commas between values.

Solution

1. Step 1: Check syntax of IN clause

   The list of values after IN must be enclosed in parentheses.

2. Step 2: Identify missing parentheses

   The query has values listed without parentheses, causing syntax error.

3. Final Answer:

   Missing parentheses around the list of values. -> Option C

4. Quick Check:

   IN requires parentheses around values [OK]

Hint: Always put parentheses around IN value list [OK]

Common Mistakes:

• Omitting parentheses around values
• Using IN with equals sign
• Forgetting commas between values

5. You want to select customers from the orders table whose country is either 'USA', 'Canada', or 'Mexico', but exclude those with status 'cancelled'. Which query correctly uses WHERE with IN and excludes cancelled orders?

hard

A. SELECT * FROM orders WHERE country IN 'USA', 'Canada', 'Mexico' AND status != 'cancelled';

B. SELECT * FROM orders WHERE country IN ('USA', 'Canada', 'Mexico') OR status != 'cancelled';

C. SELECT * FROM orders WHERE country = IN ('USA', 'Canada', 'Mexico') AND status != 'cancelled';

D. SELECT * FROM orders WHERE country IN ('USA', 'Canada', 'Mexico') AND status != 'cancelled';

Solution

1. Step 1: Use IN correctly for country filter

   The country column must be checked with IN ('USA', 'Canada', 'Mexico') without equals sign.

2. Step 2: Exclude cancelled orders with AND condition

   Use AND status != 'cancelled' to exclude those rows.

3. Final Answer:

   SELECT * FROM orders WHERE country IN ('USA', 'Canada', 'Mexico') AND status != 'cancelled'; -> Option D

4. Quick Check:

   IN filters list, AND excludes cancelled [OK]

Hint: Use AND to combine IN filter and exclusion [OK]

Common Mistakes:

• Using OR instead of AND causing wrong results
• Adding '=' before IN
• Omitting parentheses around IN values