Database Concepts

When a WHERE clause needs to test more than one condition, AND and OR combine them, exactly like in topic 21.

AND: every condition must be true

SELECT *
FROM Customers
WHERE Age > 18
  AND City = 'New York';

Returns only customers who are both older than 18 and living in New York.

OR: at least one condition must be true

SELECT *
FROM Customers
WHERE City = 'London'
   OR City = 'Paris';

Returns customers living in either London or Paris.

Multiple combined conditions

SELECT *
FROM Customers
WHERE (Age > 30 AND Country = 'USA')
   OR Country = 'France';

Returns customers who are either over-30 USA residents, or any customer from France. Brackets make the meaning unambiguous.