SQL WHERE Clause: Filter Rows with Conditions (Examples)

SQL Tutorial · Chapter 5 of 32

The SQL WHERE clause filters the rows a query works on by testing each row against a condition. Only rows where the condition is TRUE are returned by SELECT, changed by UPDATE or removed by DELETE. Without WHERE a statement touches every row, so it is the single most important clause for controlling exactly which data you get back.

SQL WHERE Syntax

SELECT column1, column2
FROM table_name
WHERE condition;

A condition compares a column with a value or another column using an operator. Text values go in single quotes, numbers and dates follow the rules of your database (dates are usually quoted too, for example '2026-01-05').

Sample Tables

Comparison Operators You Can Use in WHERE

Example 1: Filter by a Text Value

SELECT Name, City
FROM Customers
WHERE Country = 'India';

Example 2: Filter by a Number

Numbers are written without quotes. Here we find orders worth more than 100.

SELECT OrderID, Product, Amount
FROM Orders
WHERE Amount > 100;

Example 3: Not Equal To

SELECT OrderID, Product
FROM Orders
WHERE Product <> 'Laptop';

Example 4: Filter by Date

SELECT OrderID, OrderDate
FROM Orders
WHERE OrderDate >= '2026-02-01';

Example 5: WHERE in UPDATE and DELETE

WHERE is not only for SELECT. It decides which rows an UPDATE or DELETE affects, so leaving it out changes or deletes the entire table.

UPDATE Orders SET Amount = 30 WHERE OrderID = 102;
DELETE FROM Orders WHERE OrderID = 105;

After these two statements, order 102 costs 30 and order 105 no longer exists. Always run the matching SELECT with the same WHERE first to confirm which rows will be touched.

Works in MySQL, SQL Server, PostgreSQL, SQLite

• All operators above are standard in the four systems. != is accepted everywhere but <> is the ANSI form.
• Text comparison is case-insensitive by default in MySQL and SQL Server, case-sensitive in PostgreSQL and SQLite. Use LOWER(Country) = 'india' for portable matching.
• Date literals in ISO format 'YYYY-MM-DD' work in all four.

How WHERE Is Evaluated

The database tests the WHERE condition on each row, keeping it when the result is TRUE and discarding it when the result is FALSE or UNKNOWN. UNKNOWN arises from comparisons with NULL, which is why Amount <> 100 silently drops rows where Amount is missing. If the filtered column has an index, the engine jumps straight to the matching rows instead of scanning the whole table, so WHERE conditions on indexed columns such as primary keys are the fastest filters you can write.

Common Mistakes

• Missing quotes around text: WHERE City = Mumbai looks for a column called Mumbai.
• Using = NULL instead of IS NULL; nothing equals NULL, so the query returns no rows.
• Referring to a column alias from the SELECT list inside WHERE; WHERE runs before the alias exists.
• Forgetting WHERE on UPDATE or DELETE and changing every row.

Practice Exercise

1. Return the Name of every customer who is not from Australia.
2. Return OrderID and Amount for orders under 100 placed on or before 2026-02-02.

-- 1
SELECT Name FROM Customers WHERE Country <> 'Australia';
-- Anita Sharma, John Smith, Maria Garcia, Wei Chen

-- 2
SELECT OrderID, Amount FROM Orders
WHERE Amount < 100 AND OrderDate <= '2026-02-02';
-- 102 (25), 104 (45)

Related Chapters

• SQL AND, OR, NOT – combine several conditions
• SQL LIKE – pattern matching in WHERE
• SQL NULL Values – IS NULL and IS NOT NULL
• SQL from Scratch: full course overview

FAQ

What does the WHERE clause do in SQL?

It filters rows. Each row is tested against the condition and only rows where the condition is TRUE are returned, updated or deleted.

Can I use WHERE with UPDATE and DELETE?

Yes, and you almost always should. Without WHERE, UPDATE changes every row and DELETE removes every row in the table.

What is the difference between WHERE and HAVING?

WHERE filters individual rows before grouping; HAVING filters groups after GROUP BY has run. Use HAVING when the condition involves an aggregate such as COUNT or SUM.

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