WHERE

A SELECT without a filter returns every row of the table. That is fine for a table of twelve products, but a real shop can have lakhs of orders. You almost always want only some of them: today's orders, customers from Pune, products under ₹1,000.

The WHERE clause does that filtering. In this lesson you will compare numbers, text and dates, learn every comparison operator, and see the quoting mistakes that trip up most beginners.

Filtering rows with WHERE

WHERE comes after FROM and holds a condition: a test that is either true or false for each row. MySQL checks the condition row by row and keeps only the rows where it is true.

SELECT first_name, last_name, city
FROM customers
WHERE city = 'Rohtak';

first_name | last_name | city
-----------+-----------+-------
Aarav      | Sharma    | Rohtak
Vikram     | Yadav     | Rohtak
(2 rows)

Two of the twelve customers live in Rohtak. Notice the single quotes around 'Rohtak'. Text values (called strings) always go inside single quotes; numbers do not.

Comparison operators

SQL has six comparison operators:

Note that SQL uses a single = for "equal to". There is no == as in Python or JavaScript.

SELECT product_name, price
FROM products
WHERE price >= 5000;

product_name                | price
----------------------------+------
27-inch Monitor             | 15999
Noise-Cancelling Headphones | 8999
1TB External SSD            | 6499
(3 rows)

The Graphics Tablet costs ₹4,599, so it is just below the line and does not appear. With >=, a product priced exactly ₹5,000 would be included; with >, it would not.

Here is "not equal to" in action. The support team wants every order that has not been delivered yet, or never will be:

SELECT order_id, customer_id, status
FROM orders
WHERE status <> 'delivered';

order_id | customer_id | status
---------+-------------+----------
105      | 4           | cancelled
108      | 7           | shipped
111      | 9           | pending
113      | 3           | shipped
115      | 1           | pending
(5 rows)

Filtering by date

In MySQL a date is written as a string in the form 'YYYY-MM-DD': year, month, day. Because the biggest unit comes first, dates sort and compare correctly, and you can use the same operators as for numbers.

SELECT order_id, order_date, status
FROM orders
WHERE order_date >= '2025-04-01';

order_id | order_date | status
---------+------------+----------
110      | 2025-04-01 | delivered
111      | 2025-04-10 | pending
112      | 2025-04-18 | delivered
113      | 2025-05-02 | shipped
114      | 2025-05-11 | delivered
115      | 2025-05-20 | pending
(6 rows)

These are all the orders placed on or after 1 April 2025. Always use this year-first format. A date such as '01-04-2025' is not understood as a date and will not compare the way you expect.

Conditions can use calculations

The left and right sides of a comparison can be any expression, not just a column name. This query finds products where the stock is worth more than ₹1,50,000:

SELECT product_name, price, stock
FROM products
WHERE price * stock > 150000;

product_name                | price | stock
----------------------------+-------+------
Mechanical Keyboard         | 3499  | 45
27-inch Monitor             | 15999 | 18
Noise-Cancelling Headphones | 8999  | 25
1TB External SSD            | 6499  | 30
(4 rows)

MySQL works out price * stock for every row, then compares it with 150000. The calculated value does not have to appear in the SELECT list.

Common mistakes

• Forgetting the quotes around text. WHERE city = Rohtak makes MySQL look for a column called Rohtak: ERROR 1054 (42S22): Unknown column 'Rohtak' in 'where clause'. Put text in single quotes.
• Using double quotes for text. MySQL often accepts "Rohtak", but in standard SQL double quotes mean a column or table name, and some MySQL settings follow that rule. Single quotes always work.
• Writing ==. MySQL does not know == and reports a syntax error. Use a single =.
• A name with an apostrophe. To search for D'Souza, write the apostrophe twice: WHERE last_name = 'D''Souza'. A single apostrophe ends the string early and breaks the query. In application code, use prepared statements, which handle this for you.
• Using = NULL. WHERE email = NULL never finds anything. Missing values need IS NULL, explained in NULL Values.

Key points

• WHERE keeps only the rows for which its condition is true.
• The operators are =, <> (or !=), <, >, <= and >=.
• Put text and dates in single quotes; leave numbers unquoted.
• Write dates as 'YYYY-MM-DD' so they compare correctly.
• A condition can contain calculations such as price * stock.
• To combine several conditions, use AND, OR and NOT, covered in AND, OR & NOT.

SELECT product_name, price FROM products WHERE category = 'Storage';

SELECT first_name, salary FROM employees WHERE salary < 50000;

SELECT order_id, order_date FROM orders WHERE order_date < '2025-02-01';