TSQL - Create user / enable mixed auth

create-user.sql

CREATE LOGIN myUserName WITH PASSWORD = 'pwd';

USE My_Database

IF NOT EXISTS (SELECT * FROM sys.database_principals WHERE name = N'myUserName')
BEGIN
    CREATE USER [myUserName] FOR LOGIN [myUserName]
    EXEC sp_addrolemember N'db_owner', N'myUserName'
END;


-- eventually enable mixed auth for sql server:
EXEC xp_instance_regwrite N'HKEY_LOCAL_MACHINE', 
    N'Software\Microsoft\MSSQLServer\MSSQLServer', N'LoginMode', REG_DWORD, 2