DataBolt

All Lessons

Introduction to SQL

SQL Lesson 1: Your Sample Database

SQL Lesson 2: SELECT — Reading data

SQL Lesson 3: WHERE — Filtering rows

SQL Lesson 4: AND, OR, NOT

SQL Lesson 5: BETWEEN, IN, LIKE

SQL Lesson 6: NULL — The Mystery Value

SQL Lesson 7: ORDER BY

SQL Lesson 8: LIMIT & OFFSET

SQL Lesson 9: Aggregate Functions

SQL Lesson 10: GROUP BY

SQL Lesson 11: HAVING

SQL Lesson 12: INNER JOINs

SQL Lesson 13: LEFT JOINs

SQL Lesson 14: RIGHT JOINs

SQL Lesson 15: SELF JOINs

SQL Lesson 16: UNION JOINs

SQL Lesson 17: Joining Multiple Tables

SQL Lesson 18: Subqueries

SQL Lesson 19: CTEs (WITH)

SQL Lesson 20: CASE Statements

SQL Lesson 21: Window Functions

SQL Lesson 22: String Functions

SQL Lesson 23: Date & Time Functions

SQL Lesson 24: INSERT, UPDATE, DELETE

SQL Lesson 25: CREATE TABLE & DDL

SQL Lesson 26: Indexes & Performance

SQL Lesson 27: Transactions & ACID

SQL Lesson 28: SQL Execution Order

SQL Lesson 29: 50 Practice Problems

CHAPTER 4

FILTERING - WHERE

WHERE filters which rows come back. Without it, you get every row.

IN THIS CHAPTER

Filtering rows with a single condition
All comparison operators: =, !=, >, <, >=, <=
Filtering numbers, text, and dates

🌟 Think of it this way: WHERE is the bouncer at the door. Only rows that satisfy the condition get through to your result. Everyone else it turned away.

4.1 - Basic Syntax

SQL

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

4.2 -All Comparison Operators

OPERATOR	MEANING	EXAMPLE
=	Exact equal	department = 'IT'
!= or <>	Not equal	status != 'completed'
>	Greater than	salary > 70000
<	Less than	salary < 60000
>=	Greater than or equal	slalary >= 72000
<=	Less than or equal	salary <= 62000

Find employees more than 70000

SELECT name, salary 
FROM employees
WHERE salary > 70000;

Exercise 👇

Exercise:

Tasks

1.👉Find all employees who work in the IT department

2.Find employees with salary greater than 60000.

3.Find employees who work in IT and earn more than 60000.

4.Find employees who are in HR or Marketing.

5.Find employees who do not have a manager.

Stuck? Read this task's