Reference

SQL WHERE Operators

The operators you use to keep only the rows you care about.

WHERE runs once per row and keeps the rows where the condition is true. Rows where the condition is false or NULL are dropped.

Practice

Practice WHERE Practice AND, OR, and parentheses Practice IN and NOT IN Practice BETWEEN Practice LIKE

Comparison operators

Operator	Meaning	Example
`=`	Equal to	`status = 'shipped'`
`<>` or `!=`	Not equal to	`status <> 'cancelled'`
`<` `<=`	Less than / or equal	`price <= 10`
`>` `>=`	Greater than / or equal	`quantity_on_hand > 0`

Combining conditions

AND / OR / parentheses

select *
from   products
where  category_id = 1
  and  (price < 10 or quantity_on_hand = 0)

AND binds tighter than OR, so use parentheses whenever you mix them. Otherwise the query may match far more rows than you expect.

IN vs OR

Use IN when one column can equal any value in a short list. Use OR when the alternatives are different columns or different comparisons.

Equivalent filters

where state = 'PA'
   or state = 'OR'
   or state = 'FL'

where state in ('PA', 'OR', 'FL')

Set, range, and pattern operators

Operator	Use	Example
`IN`	Match any value in a list	`state in ('PA', 'NY', 'OH')`
`NOT IN`	Match none of a list	`status not in ('cancelled', 'refunded')`
`BETWEEN`	Inclusive range	`price between 10 and 25`
`LIKE`	Pattern match (`%` = any, `_` = one)	`product_name like '%seed%'`
`IS NULL`	Missing value	`shipped_date is null`

Watch out

NOT IN behaves surprisingly when the list contains a NULL: it can filter out every row. Prefer NOT EXISTS or add ... is not null when the column may be null. See Null handling.

Dialect note

LIKE is case-sensitive in DuckDB and Postgres. Use ILIKE for case-insensitive matching in both. In MySQL, LIKE is usually case-insensitive by default, and SQLite ignores case for ASCII letters.

Lesson

SQL WHERE: Filtering Rows

Use WHERE to keep only matching rows.

Cheatsheet

SQL Query Basics Cheatsheet

SELECT, WHERE, ORDER BY, and LIMIT at a glance.

Mistake

Why My Query Returns No Rows

Debug filters that match nothing.

Lesson

SQL AND, OR, and Parentheses

Combine filters without changing the intended logic.