WHERE: picking rows

Lesson 2 of 21 · Part 1 · Querying data · about 15 minutes

The queries in the last lesson gave back every row in the table. Most of the time you want only some of them: the cheap products, the customers in London, the orders that haven't shipped. That's what WHERE does:

1SELECT name, price2FROM products3WHERE price < 10;

Of the 10 products, only these 4 cost less than 10.

How WHERE picks rows

After WHERE comes a condition. The database takes the whole table and looks at it one row at a time: if the condition is true, the row stays; if not, the row is dropped. Only then does SELECT pick the columns to show.

1SELECT name, stock2FROM products3WHERE stock > 50;

Press Step on this one to see each stage: first the 10 rows that FROM gets, then WHERE marking each row as kept or dropped, and last SELECT keeping only two columns.

The clauses of a query always come in this order: SELECT, FROM, WHERE. By habit each clause starts its own line, which keeps the query easy to read.

Comparisons

These are the comparisons you'll use most in a condition:

Note that "equal" in SQL is a single =. Which product is sold out?

1SELECT name, stock2FROM products3WHERE stock = 0;

Employees who earn 4000 or more:

1SELECT name, title, salary2FROM employees3WHERE salary >= 4000;

Tip: MySQL also accepts !=, which means the same as <>. <> is the standard way to write it and works in every database.

1SELECT name, price2FROM products3WHERE price >= 15;

Text needs quotes

Numbers are written as they are; text (also called a string) goes in single quotes. Which orders haven't shipped yet?

1SELECT id, customer_id, status2FROM orders3WHERE status = 'pending';

Not equal works the same way. Every order except the shipped ones:

1SELECT id, status2FROM orders3WHERE status <> 'shipped';

Forget the quotes and you get an error:

1SELECT name2FROM customers3WHERE city = London;

ERROR 1054 (42S22): Unknown column 'London' in 'where clause'

Without quotes, the database takes London for a column name, and the table has no such column, so it says it doesn't know a column called London. Write 'London' and it works.

Text has to match exactly: 'London UK' finds no rows. That isn't an error; the result is just empty. By default MySQL ignores the case of letters ('london' and 'London' count as equal); other databases may not.

Dates

Dates go in quotes too, written as 'year-month-day', like '2025-07-01'. Comparing dates means comparing earlier and later: the later date is the "bigger" one. Customers who joined on or after July 1:

1SELECT name, joined2FROM customers3WHERE joined >= '2025-07-01';

Orders from before September 20:

1SELECT id, order_date2FROM orders3WHERE order_date < '2025-09-20';

The condition's columns needn't be selected

A column used in WHERE doesn't have to appear after SELECT. This query picks products by category, yet shows only their names:

1SELECT name2FROM products3WHERE category = 'Kitchen';

Practice

Write the query, then press Check. A hint costs nothing; the answer is there when you need it.

1SELECT name, price2FROM products;

1SELECT name, email2FROM customers3WHERE city = Paris;

1SELECT id, order_date2FROM orders;

What you learned

• WHERE condition keeps only the rows where the condition is true; the clauses go SELECT, FROM, WHERE.
• Compare with =, <>, <, >, <=, >=; equal is a single =.
• Text and dates go in single quotes; text without quotes is taken for a column name and gives ERROR 1054.
• Dates are written 'year-month-day', and comparing them means earlier and later.
• A column used in WHERE doesn't have to be in SELECT.