SQL Server/T-SQL Tutorial/System Functions/sp GrantDbAccess

A statement that grants access to a database for a SQL Server login ID

EXEC sp_GrantDbAccess JohnDoe

System stored procedures for granting and revoking access to the current database

The syntax for sp_GrantDbAccess
sp_GrantDbAccess [@loginame = ] "login_ID"
               [,[@name_in_db  = ] "database_alias"]
The syntax for sp_RevokeDbAccess
sp_RevokeDbAccess "name_in_db"
Statements that use these procedures