SQL WHERE — Filter Rows with Conditions

Filter Flow

Rows filtered by WHERE

Sample Data

usersjson

1| user_id | email               | is_active |
2|---------|---------------------|-----------|
3| 1       | [email protected]   | true      |
4| 2       | [email protected]     | false     |
5| 3       | [email protected]   | true      |

ordersjson

1| order_id | customer_id | status   | total_amount |
2|----------|-------------|----------|--------------|
3| 1001     | 1           | paid     | 49.99        |
4| 1002     | 1           | shipped  | 12.50        |
5| 1003     | 3           | pending  | 8.00         |

Comparison Operators

Active users onlyjson

1SELECT email
2FROM users
3WHERE is_active = TRUE;

Expected outputjson

1| email |
2|---|
3| [email protected] |
4| [email protected] |

Orders over $20json

1SELECT order_id, total_amount
2FROM orders
3WHERE total_amount > 20;

Expected outputjson

1| order_id | total_amount |
2|---|---|
3| 1001 | 49.99 |

AND / OR

Expression	True when
A AND B	Both A and B are true
A OR B	Either A or B is true
NOT A	A is false

Paid or shipped orders over $10json

1SELECT order_id, status, total_amount
2FROM orders
3WHERE total_amount > 10
4  AND (status = 'paid' OR status = 'shipped');

IN, BETWEEN, LIKE

IN — match any value in a listjson

1SELECT email FROM users
2WHERE user_id IN (1, 3);

BETWEEN — inclusive rangejson

1SELECT order_id, total_amount FROM orders
2WHERE total_amount BETWEEN 8 AND 15;

LIKE — pattern matchjson

1SELECT email FROM users
2WHERE email LIKE '%@example.com';

IS NULL

Never use = NULL

WHERE phone = NULL is always unknown. Use IS NULL or IS NOT NULL.

Correct NULL checkjson

1SELECT email FROM users WHERE phone IS NULL;

Common Mistakes

Using = NULL instead of IS NULL.
OR without parentheses changing logic unintentionally.
Leading wildcard LIKE '%text' — often cannot use indexes efficiently.

Practice Prompts

Find orders with status pending.
Find users whose email contains alice.
Find orders with total between 10 and 50 inclusive.

Try These Tools

SQL Query Explainer

Understand complex WHERE logic

Open tool

SQL Linter

Catch risky patterns in filters

Open tool

Continue Learning

SELECT & FROM

Reading data before filtering

ORDER BY & LIMIT

Sort and paginate filtered rows

Frequently Asked Questions

Where does WHERE run in a query?

Logically, WHERE filters rows before SELECT projects columns and before ORDER BY sorts. Only matching rows continue.

Why does WHERE status = NULL fail?

NULL is unknown, not equal to anything. Use IS NULL or IS NOT NULL instead.

What is the difference between LIKE and =?

= matches exact values. LIKE matches patterns with % (any length) and _ (one character) wildcards.

Do I need parentheses with AND and OR?

Use parentheses when mixing AND/OR to make intent explicit: WHERE (a OR b) AND c.

Can WHERE filter on multiple tables?

Not directly — use JOIN first, then filter on joined columns, or use a subquery (covered later).