primary key constraint in SQL queries

Question

Why and what is the use of naming to a primary key constraint?

create table users(
   id int
   , lastname varchar(255)
   , firstname varchar(255)
   , age int
   , **constraint pk** primary key(id, lastname)
);

Answer 1

The purpose of naming a constraint is primarily so you can understand error messages when the constraint is violated.

A secondary reason is for dropping the constraint. It is much easier to find the constraint when it has a meaningful name.

That said, in tables that I create, the primary key is usually a synthetic key -- set automatically via auto_increment for instance. And I don't drop primary key constraints. So I don't bother naming them.