[ @loginame = ] 'login'

Is the name of the login. login is sysname, with no default.

[ @passwd = ] 'password'

Is the login password. password is sysname, with a default of NULL.

Security Note:
Do not use a blank password. Use a strong password.

[ @defdb = ] 'database'

Is the default database of the login (the database to which the login is first connected after logging in). database is sysname, with a default of master.

[ @deflanguage = ] 'language'

Is the default language of the login. language is sysname, with a default of NULL. If language is not specified, the default language of the new login is set to the current default language of the server.

[ @sid = ] 'sid'

Is the security identification number (SID). sid is varbinary(16), with a default of NULL. If sid is NULL, the system generates a SID for the new login. Despite the use of a varbinary data type, values other than NULL must be exactly 16 bytes in length, and must not already exist. Specifying sid is useful, for example, when you are scripting or moving SQL Server logins from one server to another and you want the logins to have the same SID on different servers.

[ @encryptopt = ] 'encryption_option'

Specifies whether the password is passed in as clear text or as the hash of the clear text password. Note that no encryption takes place. The word "encrypt" is used in this discussion for the sake of backward compatibility. If a clear text password is passed in, it is hashed. The hash is stored. encryption_option is varchar(20), and can be one of the following values.

Value	Description
NULL	The password is passed in clear. This is the default.
skip_encryption	The password is already hashed. The Database Engine should store the value without re-hashing it.
skip_encryption_old	The supplied password was hashed by an earlier version of SQL Server. The Database Engine should store the value without re-hashing it. This option is provided for upgrade purposes only.

0 (success) or 1 (failure)

SQL Server logins can contain from 1 to 128 characters, including letters, symbols, and numbers. Logins cannot contain a backslash (\); be a reserved login name, for example sa or public, or already exist; or be NULL or an empty string ('').

If the name of a default database is supplied, you can connect to the specified database without executing the USE statement. However, you cannot use the default database until you are given access to that database by the database owner (by using sp_adduser or sp_addrolemember) or sp_addrole.

The SID number is a GUID that will uniquely identify the login in the server.

Changing the default language of the server does not change the default language of existing logins. To change the default language of the server, use sp_configure.

Using skip_encryption to suppress password hashing is useful if the password is already hashed when the login is added to SQL Server. If the password was hashed by an earlier version of SQL Server, use skip_encryption_old.

sp_addlogin cannot be executed within a user-defined transaction.

The following table shows several stored procedures that are used with sp_addlogin.

Requires ALTER ANY LOGIN permission.

A. Creating a SQL Server login

EXEC sp_addlogin 'Victoria', 'B1r12-36';
GO

B. Creating a SQL Server login that has a default database

EXEC sp_addlogin 'Albert', 'B5432-3M6', 'corporate';
GO

C. Creating a SQL Server login that has a different default language

EXEC sp_addlogin 'TzTodorov', '709hLKH7chjfwv', 'AdventureWorks', N'български'

D. Creating a SQL Server login that has a specific SID

EXEC sp_addlogin 'Michael', 'B548bmM%f6', 'AdventureWorks', 'us_english', 0x0123456789ABCDEF0123456789ABCDEF

Reference

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