I recently came across this same error while creating a database view. I was trying to use incident caller_id in a where clause. It was rather confusing because the same where clause using incident open_by worked. The key difference is that opened_by is defined on the task base table while caller_id is defined on the extended table, incident.
The solution was to lookup the "alias" for caller_id in sys_storage_alias.list and use the alias field name in the where clause. I found the alias for caller_id was a_ref_4.
I have two tables in my database view, incident (inc) and user (usr).
Where clause:
inc.opend_by = usr.sys_id - works!
inc.caller_id = usr.sys_id - failed with unknown column error
inc.a_ref_4 = usr.sys_id - works!
References:
Task table flattening
View a table hierarchy and extension model
Snehal, this may not be the solution for your issue but anyone searching for the error may find it helpful.
