sp_adduser (Transact-SQL)
Applies to: 
SQL Server
Adds a new user to the current database.
Important
This feature will be removed in a future version of SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature. Use CREATE USER instead.
Transact-SQL syntax conventions
Syntax
sp_adduser
[ @loginame = ] N'loginame'
[ , [ @name_in_db = ] N'name_in_db' ]
[ , [ @grpname = ] N'grpname' ]
[ ; ]
Arguments
[ @loginame = ] N'loginame'
The name of the SQL Server login or Windows account. @loginame is sysname, with no default. @loginame must be an existing SQL Server login or Windows account.
[ @name_in_db = ] N'name_in_db'
The name for the new database user. @name_in_db is sysname, with a default of NULL. If @name_in_db isn't specified, the name of the new database user defaults to @loginame. Specifying @name_in_db gives the new user a name in the database different from the server-level login name.
[ @grpname = ] N'grpname'
The database role of which the new user becomes a member. @grpname is sysname, with a default of NULL. @grpname must be a valid database role in the current database.
Return code values
0 (success) or 1 (failure).
Remarks
sp_adduser also creates a schema that's the name of the user.
After a user is added, use the GRANT, DENY, and REVOKE statements to define the permissions that control the activities performed by the user.
Use sys.server_principals to display a list of valid logins.
Use sp_helprole to display a list of the valid role names. When you specify a role, the user automatically gains the permissions that are defined for the role. If a role isn't specified, the user gains the permissions granted to the default public role. To add a user to a role, a value for the @name_in_db must be supplied. (@name_in_db can be the same as @loginame.)
User guest already exists in every database. Adding user guest enables this user, if it was previously disabled. By default, user guest is disabled in new databases.
sp_adduser can't be executed inside a user-defined transaction.
You can't add a guest user because a guest user already exists inside every database. To enable the guest user, grant guest CONNECT permission as shown:
GRANT CONNECT TO guest;
GO
Permissions
Requires ownership of the database.
Examples
A. Add a database user
The following example adds the database user Vidur to the existing Recruiting role in the current database, using the existing SQL Server login Vidur.
EXEC sp_adduser 'Vidur', 'Vidur', 'Recruiting';
B. Add a database user with the same login ID
The following example adds user Arvind to the current database for the SQL Server login Arvind. This user belongs to the default public role.
EXEC sp_adduser 'Arvind';
C. Add a database user with a different name than its server-level login
The following example adds SQL Server login BjornR to the current database that's a user name of Bjorn, and adds database user Bjorn to the Production database role.
EXEC sp_adduser 'BjornR', 'Bjorn', 'Production';