Select select statement condition problem. Please clarify.

Question

I found such a piece of code today

$sql = "SELECT * FROM admin_user WHERE md5(concat(id, 'SALT'))='$id' AND md5(concat(admin_pass, 'SALT') )='$pass'";

Generally select * from table name where field name=ID? Why is this an encrypted field name? How does this correspond to the id value?

Solve your doubts.