WHERE Clause

WHERE is like a sieve that only lets through the rows fitting your rule, such as all students older than ten.

In this page:

Introduction to Filtering
Filtering with Numbers
Filtering with Text
Filtering with Dates
Using Inequality Operators

Syntax

sql

SELECT column1, column2
FROM table_name
WHERE condition;

Introduction to Filtering

The WHERE clause filters a result set down to only the rows matching a specified condition, turning a query that would return an entire table into one that returns exactly the records you actually need.

Example: Introduction to Filtering

sql

SELECT * FROM users WHERE age > 18;

Filtering with Numbers

Numeric filtering uses standard comparison operators like >, <, and >= directly against a column, which is the typical way to query things like 'all products under $50' or 'users older than 18'.

Example: Filtering with Numbers

sql

SELECT * FROM products WHERE price < 20;

Filtering with Text

Text values in a WHERE condition must be wrapped in single quotes, or MySQL will misinterpret the bare word as a column name instead of a literal string and raise an error.

Example: Filtering with Text

sql

SELECT * FROM users WHERE name = 'Amit';

Filtering with Dates

Date literals also need to be quoted like text, written in the YYYY-MM-DD format MySQL expects, since an unquoted date would similarly be parsed as an invalid column reference.

Example: Filtering with Dates

sql

SELECT * FROM orders WHERE order_date = '2024-03-05';

Using Inequality Operators

The != or <> operator excludes rows matching a specific value rather than selecting for it, which is the standard way to express 'everything except this one case' in a filter.

Example: Using Inequality Operators

sql

SELECT * FROM users WHERE status != 'inactive';

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