SUBSTRING, LEFT and RIGHT in SQL Server

LEFT is the start. RIGHT is the end. SUBSTRING is a middle slice. At work: first part of a postcode, not a credit card.

Postcode area

SELECT customer_id,
       LEFT(postcode, CHARINDEX(' ', postcode + ' ') - 1) AS area
FROM Customers;

LEFT(postcode, 4) is simpler if you always want four characters. The CHARINDEX version stops at the space.

SELECT SUBSTRING(email, CHARINDEX('@', email) + 1, 200) AS domain
FROM Customers
WHERE email LIKE '%@%';