I added 5 fields on the request page (Quote 1, Quote 2, Quote 3, Quote 4, Quote 5) having follownig relationship:
TableRelation = "Purchase Header"."No." where("Document Type" = const(Quote));
In this way, all the quotes are shown in the drop down list.
I then also added two request filter fields. These are:
RequestFilterFields = Type, "No.";
"Purchase Header"."No." is a document no which is present in the table "Purchase Header" and RequestFilterfields Type and No. are present in the sub table "Purchase Line". So here I've two tables.

In the above attachement all the purchase quotations are shown in the drop down list. As different purchase quotations have different items so for instance, if I select Type = Item and No. = 1000 then in the drop down list only those quotes should be shown which have this specific item No.
I'm using BC Version 15.0. Anyone who can guide me if it is possible or not? If yes, then how can I add this functionality on the request page? Thanks for reading.