How to get the list of all database users

I am going to get the list of all users, including Windows users and 'sa', who have access to a particular database in MS SQL Server. Basically, I would like the list to look like as what is shown in SQL Server Management Studio (i.e. the list that is shown when you expand [databse] -> Security -> Users) with one important exception: I do not want to see the 'dbo' in the list. Rather, I would like to see the actual user who owns the database. So, for example, if 'sa' is the 'dbo', 'sa' must be included in the list instead of 'dbo'. Another note not to be missed is, the list in the SQL Server Management Studio normally shows Windows users in addition to SQL users, And I would like those users to be included as well.

So far, I have been able to come up with the following query:

SELECT * FROM sys.database_principals where (type='S' or type = 'U')

This query is almost right but the problem is it doesn't satisfy the 'dbo' condition.

How can I change this query or should I use another one?

For the SQL Server Owner, you should be able to use:

select suser_sname(owner_sid) as 'Owner', state_desc, *
from sys.databases

For a list of SQL Users:

select * from master.sys.server_principals

Ref. SQL Server Tip: How to find the owner of a database through T-SQL

How do you test for the existence of a user in SQL Server?

EXEC sp_helpuser

or

SELECT * FROM sysusers

Both of these select all the users of the current database (not the server).

Whenever you 'see' something in the GUI (SSMS) and you're like "that's what I need", you can always run Sql Profiler to fish for the query that was used.

Run Sql Profiler. Attach it to your database of course.

Then right click in the GUI (in SSMS) and click "Refresh".
And then go see what Profiler "catches".

I got the below when I was in MyDatabase / Security / Users and clicked "refresh" on the "Users".

Again, I didn't come up with the WHERE clause and the LEFT OUTER JOIN, it was a part of the SSMS query. And this query is something that somebody at Microsoft has written (you know, the peeps who know the product inside and out, aka, the experts), so they are familiar with all the weird "flags" in the database.

But the SSMS/GUI -> Sql Profiler tricks works in many scenarios.

SELECT
u.name AS [Name],
'Server[@Name=' + quotename(CAST(
        serverproperty(N'Servername')
       AS sysname),'''') + ']' + '/Database[@Name=' + quotename(db_name(),'''') + ']' + '/User[@Name=' + quotename(u.name,'''') + ']' AS [Urn],
u.create_date AS [CreateDate],
u.principal_id AS [ID],
CAST(CASE dp.state WHEN N'G' THEN 1 WHEN 'W' THEN 1 ELSE 0 END AS bit) AS [HasDBAccess]
FROM
sys.database_principals AS u
LEFT OUTER JOIN sys.database_permissions AS dp ON dp.grantee_principal_id = u.principal_id and dp.type = 'CO'
WHERE
(u.type in ('U', 'S', 'G', 'C', 'K' ,'E', 'X'))
ORDER BY
[Name] ASC