Lesson 3 of 26 · see the practice database

Filtering rows with WHERE

Choosing columns narrows a result from side to side. WHERE narrows it from top to bottom. It keeps only the rows that pass a test. This is the most used part of SQL, because a question about data is almost always a question about some of the rows.

The shape of WHERE

WHERE comes after FROM. It is followed by a condition. The database checks the condition for every row and returns the rows where it is true.

SELECT name, city
FROM customers
WHERE city = 'Delhi';

Only the customers from Delhi are returned. The other rows are still in the table. A SELECT never removes anything.

Comparison operators

Most databases also accept != for "not equal". <> is the standard form.

Comparing numbers

Numbers are written without quotation marks.

SELECT name, price
FROM products
WHERE price > 500;

SELECT name, stock
FROM products
WHERE stock = 0;

The second query finds the products that are sold out.

Comparing text

Text goes in single quotation marks.

SELECT name, category, price
FROM products
WHERE category = 'Stationery';

Leaving the quotation marks out is the most common mistake in this lesson. Without them, the database thinks Stationery is the name of a column.

SELECT name FROM products WHERE category = Stationery;

Error: no such column: Stationery

Is text case sensitive?

It depends on the database, and this surprises people who move from one to another. In SQLite, PostgreSQL and Oracle, 'delhi' does not equal 'Delhi'. In MySQL and SQL Server, with their usual settings, it does.

SELECT name FROM customers WHERE city = 'delhi';

No rows came back, because in the table the city is written with a capital D. The lesson on functions shows how to compare without caring about case.

Not equal

SELECT id, order_date, status
FROM orders
WHERE status <> 'delivered';

Comparing dates

In our database, dates are stored as text in the form year, month, day: '2026-03-15'. Written this way, dates sort correctly, and the comparison operators work on them just as you would hope.

SELECT id, order_date, status
FROM orders
WHERE order_date >= '2026-07-01';

Always write dates in year-month-day order with four digits for the year and two each for month and day. Every database understands that form. There is a whole lesson on dates later.

A calculation in the condition

The condition can contain a sum.

SELECT name, price, stock
FROM products
WHERE price * stock > 20000;

You can filter on a column you do not show

The column in the WHERE does not have to be in the SELECT list.

SELECT name
FROM employees
WHERE salary >= 48000;

An alias cannot be used in WHERE

This catches everyone once.

SELECT name, price * stock AS stock_value
FROM products
WHERE stock_value > 20000;

Some databases, SQLite among them, are forgiving and accept this, so the practice box may run it. Standard SQL does not, and MySQL, PostgreSQL, SQL Server and Oracle refuse. The reason is the order in which a query is carried out: the database filters the rows first and names the columns afterwards, so at the time of the WHERE, the alias does not exist yet. Repeat the calculation in the WHERE, as in the example before this one.

The order of the parts

The parts of a query must come in a fixed order. So far: SELECT, then FROM, then WHERE. Putting WHERE before FROM is an error.

Try it yourself

SELECT name, city FROM customers WHERE city = 'Mumbai';

SELECT name, price FROM products WHERE price <= 150;

SELECT id, order_date FROM orders WHERE status = 'cancelled';

Mark this lesson as done

Examples on this page were run with SQLite 3.50.4 on 12 November 2026. The results shown are the real results.

This is an independent learning site. It is not connected with the makers of any database product. MySQL, PostgreSQL, SQL Server, Oracle and SQLite are named only so that you know where a piece of SQL works. The shop, its customers and its staff in the practice database are made up.