SELECT, FROM, WHERE Basics

SELECT, FROM, WHERE Basics

SQL is the language of databases. As a tester, you will use it to verify that your application stores, retrieves, and updates data correctly. Even if you never write a stored procedure, knowing enough SQL to query the database alongside your API tests makes you dramatically more effective.

The Basic Query Structure

Every SQL query starts with three clauses:

SELECT column1, column2
FROM   table_name
WHERE  condition;

• SELECT: What columns to return (or * for all)
• FROM: Which table to query
• WHERE: Which rows to include

Your First Queries

Get all users:

SELECT * FROM users;

Get specific columns:

SELECT id, email, created_at FROM users;

Filter with WHERE:

SELECT * FROM users WHERE is_active = 1;
SELECT * FROM users WHERE email = 'test@example.com';
SELECT * FROM orders WHERE total_amount > 100.00;

Operators in WHERE Clauses

Why Testers Need This

When your API creates a user, you can verify it was stored correctly:

SELECT id, email, role, created_at
FROM   users
WHERE  email = 'newuser@example.com';

When your API reports an order total, verify the database agrees:

SELECT SUM(price * quantity) as calculated_total
FROM   order_items
WHERE  order_id = 42;

Direct database verification catches bugs that API-level testing misses — particularly around data persistence and calculation accuracy.