Alternative query to this (avoid DISTINCT) Note: I work with MSSQL 2008, but I guess it's valid for many others DB engines
I have this table "Users":


UserID  User    CountryID
1     user 1    1
2     user 2    2
3     user 3    3
4     user 4    4
5     user 5    4
6     user 6    3


And this table "Countries"


CountryID   Country
1           MX
2           USA
3           CAN
4           ENGLAND


As you can see, every user belongs to a country.

If I want to know, all the different countries where I have at least, one user on the Users table, right now I do this query:

select distinct country 
from Users inner join
countries on users.CountryID=countries.CountryID


And achieve the next result set:


CAN
ENGLAND
MX
USA 


Which is indeed, all the different countries, where I have at least one user on muy table Users.

My doubt is, is possible to achieve the above result set, with out using "DISTINCT", I mean only using JOINS and conditions ?

Here it's de DDL scripts:


USE [TEST]
GO
/****** Object:  Table [dbo].[Users]    Script Date: 09/21/2012 16:21:14 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Users](
    [UserID] [int] NULL,
    [User] [nvarchar](50) NULL,
    [CountryID] [int] NULL
) ON [PRIMARY]
GO
INSERT [dbo].[Users] ([UserID], [User], [CountryID]) VALUES (1, N'user 1', 1)
INSERT [dbo].[Users] ([UserID], [User], [CountryID]) VALUES (2, N'user 2', 2)
INSERT [dbo].[Users] ([UserID], [User], [CountryID]) VALUES (3, N'user 3', 3)
INSERT [dbo].[Users] ([UserID], [User], [CountryID]) VALUES (4, N'user 4', 4)
INSERT [dbo].[Users] ([UserID], [User], [CountryID]) VALUES (5, N'user 5', 4)
INSERT [dbo].[Users] ([UserID], [User], [CountryID]) VALUES (6, N'user 6', 3)
/****** Object:  Table [dbo].[Countries]    Script Date: 09/21/2012 16:21:14 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Countries](
    [CountryID] [int] NULL,
    [Country] [nvarchar](50) NULL
) ON [PRIMARY]
GO
INSERT [dbo].[Countries] ([CountryID], [Country]) VALUES (1, N'MX')
INSERT [dbo].[Countries] ([CountryID], [Country]) VALUES (2, N'USA')
INSERT [dbo].[Countries] ([CountryID], [Country]) VALUES (3, N'CAN')
INSERT [dbo].[Countries] ([CountryID], [Country]) VALUES (4, N'ENGLAND')
INSERT [dbo].[Countries] ([CountryID], [Country]) VALUES (5, N'BRAZIL')
You could get that same result set with the following:

select country from countries where exists 
    (select countryid from users 
        where users.countryid = country.countryid)


OR

select country from countries where countryid in 
    (select countryid from users)


Neither of these use distinct but other than that I don't know how much "better" they are.