MS SQL Server Create new User and assign to database

SQL Server Create new User and assign to database

CREATE LOGIN User_Name WITH PASSWORD = 'User123'
GO

Use YourDatabase;
GO

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