? MySQL IN

? Quick Overview

The IN operator allows you to specify multiple values in a WHERE clause. It is a concise shorthand for multiple OR conditions and can accept literals or a subquery result set.

? Key Concepts

Purpose: Match a column value against a list of possible values.
Flexibility: Values can be numbers, strings, or produced by a subquery.
Readability: Cleaner than chained OR expressions.
Case sensitivity: MySQL string comparisons are case-insensitive by default for typical collations.

? Syntax / Theory

? View Code Example

-- Syntax for IN: select specific columns where a column matches any value in the list
SELECT column1, column2, ...
FROM table_name
WHERE column_name IN (value1, value2, ...);

? Code Example(s)

? View Code Example

-- Select students who belong to either 'Science' or 'Engineering' departments
SELECT * FROM students
WHERE department IN ('Science', 'Engineering');

-- Select employees with specific IDs
SELECT * FROM employees
WHERE employee_id IN (1001, 1003, 1005);

? Live Output / Explanation

Explanation

IN: Tests whether a value equals any value in a list. Equivalent to multiple OR checks.
Subqueries: You can use IN (SELECT ...) to compare against a set returned from another query.
Performance: For very large lists, consider joins or temporary tables; for moderate lists, IN is readable and efficient.

✅ Tips & Best Practices

Use IN for filtering against a short list of known values (IDs, categories).
Prefer joins or indexed temporary tables for very large sets returned by subqueries.
Ensure string literals are quoted to avoid syntax errors.
Remember NOT IN behaves differently with NULL values — be cautious.

? Try It Yourself / Practice Tasks

Write a query to find all employees whose departments are either 'HR' or 'Sales'.
Use IN to find all students who have taken any of the courses 'Math', 'History', or 'Physics'.
Experiment with a subquery: WHERE id IN (SELECT user_id FROM subscriptions WHERE active=1).