Why is there a collation conflict between system views

Question

I'm using the following statement to retrieve a list of triggers from the database:

select tr.name
from sys.triggers tr
union all
select tr.name
from sys.server_triggers tr;

However on my local SQL Server 2012 Express installation this fails with the error:

Cannot resolve collation conflict between "Latin1_General_CI_AS" and "Latin1_General_CI_AI" in UNION ALL operator occurring in SELECT statement column 1

I can "fix" this by changing the statement to explicitely use a different collation in the second part of the union:

select tr.name
from sys.triggers tr
union all
select tr.name collate database_default as name
from sys.server_triggers tr;

However I feel this is an ugly hack, and I don't really understand why there is a conflict in the first place. Both views ultimately retrieve the name from sys.sysschobjs.name and thus all values should have the same collation.

So my two questions are:

1. why is there a collation conflict in the first place?
2. is it safe to use collate database_default only in the second part, or should I better use it for both queries (performance is not an issue for this).

Interesting enough the same query does not create a problem when using it against a SQL Server 2005 (standard edition) with the same triggers defined.

Answer 1

sys.server_triggers is a server view, so it has the server collation. sys.triggers is a database view, so it has the database collation. You have a DB that has a collation different from the server. QED. Repro:

create database foo collate Latin1_General_CI_AI

use foo

select tr.name
from sys.triggers tr
union all
select tr.name
from sys.server_triggers tr;