Difference between a User and a Login in SQL Server

I have recently been running into many different areas of SQL Server that I normally don't mess with. One of them that has me confused is the area of Logins and Users. Seems like it should be a pretty simple topic...

It appears that each login can only have 1 user and each user can only have 1 login.

A login can be associated to multiple tables thus associating that user to many tables.

So my question is why even have a login and a user? they seem to be pretty much one in the same. What are the differences, or what is it that I seem to be missing?


  • A "Login" grants the principal entry into the SERVER.

    A "User" grants a login entry into a single DATABASE.

    One "Login" can be associated with many users (one per database).

    Each of the above objects can have permissions granted to it at its own level. See the following articles for an explanation of each