why is this query invalid?

Question

Why is this query invalid? When I write just SRV_ID instead of vt_exam_details.SRV_ID everything works just fine

 cl_id
, cl_name_last as CUSTOMER
, vt_animals.an_type
, vt_exam_details.SRV_ID
, vt_services.srv_desc
, vt_exam_details.ex_fee
from vt_clients
join vt_animals using (cl_id)
join vt_exam_headers using (an_id)
join vt_exam_details using (ex_id)
join vt_services using (srv_id)

Error:

Error at Command Line:5 Column:3
Error report:
SQL Error: ORA-00904: "VT_EXAM_DETAILS"."SRV_ID": invalid identifier
00904. 00000 -  "%s: invalid identifier"
*Cause:    
*Action:

Thanks.

Answer 1

因为表vt_exam_details不在FROM子句中？

Answer 2

VT_EXAM_DETAILS表中是否有SRV_ID？