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What is WHERE?

Learn to filter rows by a condition with WHERE.

What is WHERE?

The WHERE clause filters rows in a query by a condition. Only rows that meet the condition are returned.

SELECT name, price
FROM products
WHERE price > 10;

This returns only products whose price is greater than 10. WHERE comes after FROM and before ORDER BY.

name, price is selected from products. WHERE keeps only the rows where price > 10 holds.

What is WHERE? — details

WHERE is the heart of the query; it keeps rows whose condition evaluates to true. The condition combines columns, constants and operators. Only matching rows appear in the result.

For example, WHERE city = 'İzmir' returns only customers in İzmir; without WHERE every row of the table is returned.

Practice What is WHERE?

Select name and price from products where price is greater than 10.

Starter code

query.sql
-- add the condition
SELECT name, price
FROM
WHERE

Sample solution

query.sql
SELECT name, price
FROM products
WHERE price > 10

Expected output

name   price
Defter 12
Çanta  25

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Where does WHERE go?

  • Before FROM
  • Before SELECT
  • After FROM Correct answer
  • At the very end

Explanation: WHERE comes after FROM.

2 Equality condition

Question 
SELECT name FROM customers
WHERE city ____ 'İstanbul';
Answer 
SELECT name FROM customers
WHERE city = 'İstanbul';

Explanation: SQL uses a single = for equality; text values go in single quotes.

3 What is WHERE: match the terms

Term Meaning
= equal
<> not equal
< less than
> greater than

All lessons in Beginner

1 SELECT basics

  1. What is SELECT?
  2. Selecting all columns
  3. Selecting specific columns
  4. Column aliases with AS
  5. Literal values
  6. Summary - SELECT basics

2 WHERE filtering

  1. What is WHERE?
  2. Comparison operators
  3. AND and OR
  4. IN and BETWEEN
  5. Pattern matching with LIKE
  6. Summary - WHERE filtering

3 Ordering and limit

  1. ORDER BY
  2. ASC and DESC
  3. Multi-column ordering
  4. LIMIT
  5. OFFSET
  6. Summary - Ordering and limit

4 Project: CRUD app

  1. Project design
  2. Reading data
  3. Inserting data
  4. Updating data
  5. Deleting data

5 Data types

  1. Integer types
  2. Decimal types
  3. CHAR and VARCHAR
  4. DATE and TIME
  5. BOOLEAN
  6. Summary - Data types

6 Operators

  1. Arithmetic operators
  2. Comparison operators
  3. Logical operators
  4. IS NULL
  5. String concatenation
  6. Summary - Operators

7 String functions

  1. UPPER and LOWER
  2. LENGTH
  3. SUBSTRING
  4. TRIM
  5. CONCAT
  6. Summary - String functions

8 Project: Shopping cart

  1. Cart design
  2. Listing products
  3. Adding to cart
  4. Calculating total
  5. Removing from cart

9 Number functions

  1. ROUND
  2. CEIL and FLOOR
  3. ABS
  4. POWER and SQRT
  5. MOD
  6. Summary - Number functions

10 Date functions

  1. CURRENT_DATE and NOW
  2. EXTRACT
  3. Date arithmetic
  4. DATEDIFF
  5. Date formatting
  6. Summary - Date functions

11 NULL handling

  1. What is NULL?
  2. IS NULL
  3. COALESCE
  4. NULLIF
  5. Three-valued logic
  6. Summary - NULL handling

12 DISTINCT

  1. What is DISTINCT?
  2. DISTINCT on one column
  3. Multi-column DISTINCT
  4. DISTINCT with aggregates
  5. DISTINCT vs GROUP BY
  6. Summary - DISTINCT

13 INSERT

  1. INSERT basics
  2. Inserting into specific columns
  3. Multiple rows
  4. INSERT with SELECT
  5. DEFAULT values
  6. Summary - INSERT

14 UPDATE

  1. UPDATE basics
  2. Conditional UPDATE
  3. Multi-column UPDATE
  4. Calculated updates
  5. UPDATE pitfalls
  6. Summary - UPDATE

15 DELETE

  1. DELETE basics
  2. Conditional DELETE
  3. DELETE vs TRUNCATE
  4. Emptying a table
  5. Safe deletion
  6. Summary - DELETE

16 CREATE TABLE

  1. CREATE TABLE basics
  2. Column definitions
  3. NOT NULL
  4. DEFAULT
  5. PRIMARY KEY
  6. Summary - CREATE TABLE

17 Constraints

  1. UNIQUE constraint
  2. CHECK constraint
  3. FOREIGN KEY
  4. CASCADE
  5. Constraint management
  6. Summary - Constraints

18 Simple JOIN

  1. What is JOIN?
  2. INNER JOIN
  3. The ON clause
  4. Table aliases
  5. Multi-table JOIN
  6. Summary - Simple JOIN

19 Project: Inventory system

  1. Inventory design
  2. Product table
  3. Stock movements
  4. Stock report
  5. Low stock alert

20 Beginner final

  1. Customer query
  2. Order report
  3. Data update
  4. Table redesign