SQL WHERE Clause Explained

Quick answer

The WHERE clause filters rows in a SQL query. It tells SQL which rows should stay in the result and which rows should be excluded.

SELECT column_name
FROM table_name
WHERE condition;

Without WHERE, a query usually returns every row in the table. With WHERE, you only get the rows that match the condition.

In this guide

Sample table

To keep the examples consistent, imagine this employees table:

Why WHERE matters

In real work, you rarely want every row in a table. You usually want a smaller slice of the data:

• employees in one department
• orders above a certain dollar amount
• customers in one city
• records from a certain date range

That is what WHERE is for. It turns a broad query into a useful one.

Basic filtering

The simplest use of WHERE is filtering rows by one condition.

SELECT name, salary
FROM employees
WHERE salary > 60000;

This returns only employees with salary above 60000.

Comparison operators

WHERE clauses often use comparison operators. These let you test values against a condition.

Example:

SELECT name, department
FROM employees
WHERE department = 'IT';

This returns only IT employees.

AND and OR

You can combine multiple conditions with AND and OR.

Using AND

SELECT name, department, salary
FROM employees
WHERE department = 'IT' AND salary > 80000;

This returns only rows where both conditions are true.

Using OR

SELECT name, department
FROM employees
WHERE department = 'IT' OR department = 'Sales';

This returns rows where either condition is true.

IN and BETWEEN

IN and BETWEEN are cleaner shortcuts for common filtering patterns.

Using IN

SELECT name, department
FROM employees
WHERE department IN ('IT', 'Sales');

This is a cleaner version of writing multiple OR checks for the same column.

Using BETWEEN

SELECT name, salary
FROM employees
WHERE salary BETWEEN 60000 AND 80000;

This returns salaries in that range, inclusive.

LIKE text matching

LIKE is used for pattern matching with text.

SELECT name
FROM employees
WHERE name LIKE 'A%';

This returns names that start with A.

Common wildcards:

NULL checks

NULL means “no value.” It is not the same as zero, blank text, or false.

SELECT name
FROM employees
WHERE city IS NULL;

If any rows had no city value, this query would return them.

WHERE with UPDATE and DELETE

WHERE is not only used with SELECT. It is also critical with UPDATE and DELETE.

UPDATE example

UPDATE employees
SET city = 'Boston'
WHERE employee_id = 2;

This changes only Ben’s city.

DELETE example

DELETE FROM employees
WHERE employee_id = 3;

This deletes only Chris’s row.

Common mistakes

• using = NULL instead of IS NULL
• forgetting quotes around text values like 'IT'
• confusing AND and OR
• writing conditions that are broader than intended
• forgetting that WHERE is critical in UPDATE and DELETE queries

Practice questions

Bottom line

The WHERE clause is one of the most important parts of SQL because it controls which rows you actually work with.

Once you understand basic conditions, AND, OR, IN, BETWEEN, LIKE, and NULL checks, your queries become much more useful.

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