Requisition Header DFF issue

Summary

Unbale to create DFF with Valdation type "Table"

Content

Hi Experts,

I am creating DFF in Requisition page. The DFF validation type is Table. We are pulling value from PPM area. To pull this we need to put join condition between 3 tables. In from clause system not allowing me to add 3 tables. Here is my query. Can any body check and help on this.

Select PT.CLASS_CODE
From 
PJF_CLASS_CODES_TL PT,
PJF_PROJECT_CLASSES PRC,
PJF_PROJECTS_ALL_B PB
where PT.CLASS_CODE_ID=PRC.CLASS_CODE_ID
AND PRC.class_category_id='300000007280875'