Filtering with WHERE

The WHERE clause lets you filter rows based on conditions. Instead of getting every row, you get only the ones that match your criteria.

Basic Syntax

SELECT columns
FROM table
WHERE condition;

Comparison Operators

Operator	Meaning	Example
=	Equal to	price = 29.99
<> or !=	Not equal	category <> 'Office'
>	Greater than	price > 100
<	Less than	stock < 50
>=	Greater than or equal	price >= 100
<=	Less than or equal	stock <= 20

Filtering Numbers

-- Products priced over $100
SELECT name, price
FROM products
WHERE price > 100;

Result:

name              | price
------------------+---------
Laptop Pro 15"    | 1299.99
Standing Desk     | 449.99
Office Chair      | 299.99

Filtering Text

-- Only electronics
SELECT name, price, stock
FROM products
WHERE category = 'Electronics';

Important: Text values must be in single quotes ('Electronics'), not double quotes.

Combining Conditions with AND / OR

-- Electronics under $100
SELECT name, price
FROM products
WHERE category = 'Electronics'
  AND price < 100;

-- Furniture OR items costing more than $1000
SELECT name, category, price
FROM products
WHERE category = 'Furniture'
   OR price > 1000;

Negation with NOT

-- Everything except Office supplies
SELECT name, category
FROM products
WHERE NOT category = 'Office';

-- Equivalent shorthand
SELECT name, category
FROM products
WHERE category <> 'Office';

IN — Match Multiple Values

Instead of chaining OR conditions, use IN:

-- Products in Electronics or Furniture
SELECT name, category
FROM products
WHERE category IN ('Electronics', 'Furniture');

NOT IN excludes those values:

SELECT name, category
FROM products
WHERE category NOT IN ('Office');

BETWEEN — Range Filtering

-- Products priced between $50 and $500 (inclusive)
SELECT name, price
FROM products
WHERE price BETWEEN 50 AND 500;

Equivalent to price >= 50 AND price <= 500.

LIKE — Pattern Matching

Use LIKE for partial text matches:

• % matches any sequence of characters
• _ matches exactly one character

-- Users whose name starts with "A"
SELECT name, email
FROM users
WHERE name LIKE 'A%';