0 how to hack website using sql injection

Sql injection is a technique to hack the website.Here i am going to tell something about sql injection.

for example whenever you create login page of any website you wrote the below code to read the username and password from the table.

select * from table-name where username = 'use-rid' and password ='pwd'

when you will execute this query in sql you will find the record of the matching data of the query.

if you pass this qry as an input

Username: ' OR 'z'='z Password: ' OR 'z'='z

then you will find the all record are get as output