Module 1: SQL Foundations•45 min

Logical Operators: AND, OR, NOT

Progress Tracking

Combining Conditions

A single WHERE condition gets you pretty far, but real questions usually need more:

Find employees in HR who earn over 80,000
Show me orders from March or April
Get everyone except the Admin department

That's where AND, OR, and NOT come in. They let you combine multiple conditions into one filter.

AND: Both Conditions Must Be True

SQL

SELECT *
FROM orders
WHERE order_details = 'Coat'
  AND total_order_cost > 100;

Table: techcorp_workforce

id	first_name	last_name	department	salary	phone_number	joining_date
1	Sarah	Mitchell	HR	95000	555-0101	2021-03-15
2	Michael	Chen	HR	88000	555-0102	2022-06-01
3	Emily	Rodriguez	HR	82500		2021-09-20
4	David	Park	HR	80000	555-0104	2023-01-10
5	Lisa	Thompson	HR	65000		2021-04-05

Tables: techcorp_workforce

Both conditions must be true for a row to be included.

Chaining Multiple ANDs

You can chain as many ANDs as you need. Try adding a third condition — what happens if you also filter for employees who joined after January 1, 2022?

Tables: techcorp_workforce

Each AND adds another filter, narrowing your results.

Churro Activity Date

Table: los_angeles_restaurant_health_inspections

serial_number	activity_date	facility_name	score	grade	service_code	service_description	employee_id	facility_address	facility_city	facility_id	facility_state	facility_zip	owner_id	owner_name	pe_description	program_element_pe	program_name	program_status	record_id
DAQHRSETQ	2017-06-08	MARGARITAS CAFE	93	A	1	ROUTINE INSPECTION	EE0000006	5026 S CRENSHAW BLVD	LOS ANGELES	FA0023656	CA	90043	OW0004133	BAZAN, ASCENCION	RESTAURANT (61-150) SEATS HIGH RISK	1638	MARGARITAS CAFE	ACTIVE	PR0011718
DA2GQRJOS	2017-03-07	LAS MOLENDERAS	97	A	1	ROUTINE INSPECTION	EE0000997	2635 WHITTIER BLVD	LOS ANGELES	FA0160416	CA	90023	OW0125379	MARISOL FEREGRINO	RESTAURANT (0-30) SEATS HIGH RISK	1632	LAS MOLENDERAS	INACTIVE	PR0148504
DAMQTA46T	2016-03-22	SANDRA'S TAMALES	93	A	1	ROUTINE INSPECTION	EE0001049	5390 WHITTIER BLVD	LOS ANGELES	FA0171769	CA	90022-4032	OW0178828	SANDRA'S TAMALES INC.	RESTAURANT (0-30) SEATS MODERATE RISK	1631	SANDRA'S TAMALES	ACTIVE	PR0164225
DAXMBTIRZ	2018-02-12	CAFE GRATITUDE	97	A	1	ROUTINE INSPECTION	EE0000828	639 N LARCHMONT BLVD STE #102	LOS ANGELES	FA0058921	CA	90004	OW0005704	CAFE GRATITUDE LARCHMONT LLC	RESTAURANT (61-150) SEATS HIGH RISK	1638	CAFE GRATITUDE	ACTIVE	PR0019854
DAK8TBMS0	2015-09-10	THE WAFFLE	90	A	1	ROUTINE INSPECTION	EE0000709	6255 W SUNSET BLVD STE #105	LOS ANGELES	FA0051830	CA	90028	OW0035796	THE WAFFLE, LLC	RESTAURANT (61-150) SEATS HIGH RISK	1638	THE WAFFLE	ACTIVE	PR0010922

Tables: los_angeles_restaurant_health_inspections

SQL

SELECT
  first_name,
  last_name,
  department
FROM techcorp_workforce
WHERE department = 'HR'
  OR department = 'Admin';

A row only needs to match one condition to be included. HR employees are in, Admin employees are in, Engineering employees are out.

Use IN for Multiple Values on the Same Column

When checking the same column for multiple values, IN (covered next lesson) is often cleaner than chaining ORs.

Lyft Driver Wages

Table: lyft_drivers

index	start_date	yearly_salary
0	2018-04-02	48303
1	2018-05-30	67973
2	2015-04-05	56685
3	2015-01-08	51320
4	2017-03-09	67507

Tables: lyft_drivers

NOT: Exclude Matches

NOT reverses a condition. It gives you everything that doesn't match.

SQL

SELECT
  first_name,
  last_name,
  department
FROM techcorp_workforce
WHERE NOT department = 'Admin';

This is equivalent to:

SQL

WHERE department <> 'Admin'

Both work. Use whichever reads more naturally for your situation.

NOT Is Most Useful with IN, BETWEEN, and LIKE

NOT is more powerful when combined with other operators. For example: WHERE NOT department IN ('Admin', 'HR')

Try It

Tables: techcorp_workforce

Combining AND and OR

This is where things get tricky. When you mix AND and OR, SQL evaluates AND first. This can lead to unexpected results.

Let's say you want employees in HR or Engineering, but only those earning over 80,000. You might write:

SQL

-- This doesn't do what you think!
SELECT
  first_name,
  department,
  salary
FROM techcorp_workforce
WHERE department = 'HR'
  OR department = 'Engineering'
  AND salary > 80000;

Because AND is evaluated first, SQL reads this as:

SQL

WHERE department = 'HR'
  OR (department = 'Engineering' AND salary > 80000)

So you get ALL HR employees (regardless of salary) plus Engineering employees earning over 80,000. Not what you wanted.

Use Parentheses to Control Order

Tables: techcorp_workforce

The corrected version groups the OR conditions first, then applies the salary filter.

When in Doubt, Use Parentheses

Parentheses make your intent clear and prevent bugs. Even if they're not strictly necessary, they help whoever reads your code next — including future you.

High Earners in Support Departments

Table: techcorp_workforce

id	first_name	last_name	department	salary	phone_number	joining_date
1	Sarah	Mitchell	HR	95000	555-0101	2021-03-15
2	Michael	Chen	HR	88000	555-0102	2022-06-01
3	Emily	Rodriguez	HR	82500		2021-09-20
4	David	Park	HR	80000	555-0104	2023-01-10
5	Lisa	Thompson	HR	65000		2021-04-05

Tables: techcorp_workforce

Key Takeaways

AND requires all conditions to be true.
OR requires at least one condition to be true.
NOT excludes rows that match the condition.
AND is evaluated before OR — use parentheses to override.
When mixing AND and OR, always use parentheses to be safe.

What's Next

Chaining ORs for the same column gets tedious. Writing department = 'HR' OR department = 'Account' OR department = 'Admin' is painful. In the next lesson, you'll learn cleaner ways to filter: LIKE for pattern matching, IN for multiple values, and BETWEEN for ranges.

Next upContinue →

Pattern Matching: LIKE, IN, BETWEEN

50 min