How to check if SQL Server Tables are System Tables

Question

Using the stored procedure sp_msforeachtable it's possible to execute a script for all tables in a database.

However, there are system tables which I'd like to exclude from that. Instinctively, I would check the properties IsSystemTable or IsMSShipped. These don't work like I expect - I have for example a table called __RefactorLog:

But when I query if this is a system or MS Shipped table, SQL Server reports none of my tables are system tables:

exec (N'EXEC Database..sp_msforeachtable "PRINT ''? = '' + CAST(ObjectProperty(Object_ID(''?''), ''IsSystemTable'') AS VARCHAR(MAX))"') AS LOGIN = 'MyETLUser'
-- Results of IsSystemTable:
[dbo].[__RefactorLog] = 0
[schema].[myUserTable] = 0

and

exec (N'EXEC Database..sp_msforeachtable "PRINT ''? = '' + CAST(ObjectProperty(Object_ID(''?''), ''IsMSShipped'') AS VARCHAR(MAX))"') AS LOGIN = 'MyETLUser'

-- Results of IsMSShipped:
[dbo].[__RefactorLog] = 0
[schema].[myUserTable] = 0

When I look into the properties of the table (inside SSMS), the table is marked as a system object. An object property like IsSystemObject doesn't exist though (AFAIK).

How do I check if a table is a system object, apart from the object property? How does SSMS check if a table is a system object?

Answer 1

Management studio 2008 seems to run some quite ugly following code when opening the "System Tables" folder in the object explorer, the key bit seems to be:

CAST(
 case 
    when tbl.is_ms_shipped = 1 then 1
    when (
        select 
            major_id 
        from 
            sys.extended_properties 
        where 
            major_id = tbl.object_id and 
            minor_id = 0 and 
            class = 1 and 
            name = N''microsoft_database_tools_support'') 
        is not null then 1
    else 0
end          
             AS bit) AS [IsSystemObject]

(Where tbl is an alias for sys.tables)

So it seems that it's a combination - either is_ms_shipped from sys.tables being 1, or having a particular extended property set.