Identifying Duplicate Page Titles while merging several spaces

First, you can have attachments of the same name in a space so they shouldn't be causing the problem.

here is a SQL query (mssql & pgsql) that should give you duplicate names between spaces

select
c.title
from content c, spaces s 
where c.contenttype='PAGE' 
and c.content_status='current'
and c.prevver is null 
and c.spaceid=s.spaceid
and s.spacekey in ('SPACEKEY1', 'SPACEKEY2')
group by c.title having count(*) > 1

Just replace your space keys for the examples in the 2nd last line. It ignores deleted pages & only checks the titles of the current version of pages.

if you want a report of all the pages, this will also work

select

c.contentid
, c.title
, c.content_status
, s.spacename
, s.spacekey

from content c, spaces s 
where c.contenttype='PAGE' 
and c.content_status='current'
and c.prevver is null 
and c.spaceid=s.spaceid
and s.spacekey in ('SPACEKEY1', 'SPACEKEY2')
order by c.title