in sql query code example

Example 1: sql in

Used alongside a WHERE clause as a shorthand for multiple OR conditions.
So instead of:
SELECT * FROM users
WHERE country = 'USA' OR country = 'United Kingdom' OR
country = 'Russia' OR country = 'Australia';
You can use:
SELECT * FROM users
WHERE country IN ('USA', 'United Kingdom', 'Russia',
'Australia');

Example 2: in query in sql

SELECT Id, FirstName, LastName, Country  FROM Customer WHERE Country IN        (SELECT Country           FROM Supplier)