Difference between a User and a Login in SQL Server

Sql Sql Server Sql Server-2005

Sql Problem Overview

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?

Sql Solutions

Solution 1 - Sql

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

Solution 2 - Sql

One reason to have both is so that authentication can be done by the database server, but authorization can be scoped to the database. That way, if you move your database to another server, you can always remap the user-login relationship on the database server, but your database doesn't have to change.

Solution 3 - Sql

I think there is a really good MSDN blog post about this topic by Laurentiu Cristofor:

> The first important thing that needs to be understood about SQL Server > security is that there are two security realms involved - the server > and the database. The server realm encompasses multiple database > realms. All work is done in the context of some database, but to get > to do the work, one needs to first have access to the server and then > to have access to the database. > > Access to the server is granted via logins. There are two main > categories of logins: SQL Server authenticated logins and Windows > authenticated logins. I will usually refer to these using the shorter > names of SQL logins and Windows logins. Windows authenticated logins > can either be logins mapped to Windows users or logins mapped to > Windows groups. So, to be able to connect to the server, one must have > access via one of these types or logins - logins provide access to the > server realm. > > But logins are not enough, because work is usually done in a database > and databases are separate realms. Access to databases is granted via > users. > > Users are mapped to logins and the mapping is expressed by the SID > property of logins and users. A login maps to a user in a database if > their SID values are identical. Depending on the type of login, we can > therefore have a categorization of users that mimics the above > categorization for logins; so, we have SQL users and Windows users and > the latter category consists of users mapped to Windows user logins > and of users mapped to Windows group logins. > > Let's take a step back for a quick overview: a login provides access > to the server and to further get access to a database, a user mapped > to the login must exist in the database.

that's the link to the full post.

Solution 4 - Sql

In Short,

Logins will have the access of the server.

and

Users will have the access of the database.

Solution 5 - Sql

I think this is a very useful question with good answer. Just to add my two cents from the MSDN Create a Login page:

> A login is a security principal, or an entity that can be authenticated by a secure system. Users need a login to connect to SQL Server. You can create a login based on a Windows principal (such as a domain user or a Windows domain group) or you can create a login that is not based on a Windows principal (such as an SQL Server login). > > Note:
> To use SQL Server Authentication, the Database Engine must use mixed mode authentication. For more information, see Choose an Authentication Mode. > > As a security principal, permissions can be granted to logins. The scope of a login is the whole Database Engine. To connect to a specific database on the instance of SQL Server, a login must be mapped to a database user. Permissions inside the database are granted and denied to the database user, not the login. Permissions that have the scope of the whole instance of SQL Server (for example, the CREATE ENDPOINT permission) can be granted to a login.

Solution 6 - Sql

Graph on logins / users from MS sql-docs

Content Type	Original Author	Original Content on Stackoverflow
Question	corymathews	View Question on Stackoverflow
Solution 1 - Sql	Scott Ivey	View Answer on Stackoverflow
Solution 2 - Sql	Tom Resing	View Answer on Stackoverflow
Solution 3 - Sql	David Leitner	View Answer on Stackoverflow
Solution 4 - Sql	Vikrant Kedari	View Answer on Stackoverflow
Solution 5 - Sql	ilmatte	View Answer on Stackoverflow
Solution 6 - Sql	frmbelz	View Answer on Stackoverflow