To all of you:

Thank you for your suggestions. After studying this situation for a few weeks and trying several options, Naomi's suggestion of using multiple SELECT statements and intermediate cursors seems to be working best for me. I was unable to accomplish what I needed in just one SELECT statement.

I have created six select statements that merge two tables each. Starting with the second SELECT statement, one of the two tables/cursors is the result set of the previous SELECT statement. I have a custom method, "mergefields" between each SELECT statement that gets data from then drops the duplicated custid and upsino data fields.

For brevity I have posted only two of the SELECT statements:

* Join the VISUAL and LIQUID tables into cursor "vl"
select * from visual v ;
	full outer join liquid l on v.custid = l.custid and v.upsino = l.upsino and v.datinp = l.puldat ;
	into cursor vl readwrite ;
	where v.custid = lcCustid and between(v.upsino, lcStartUpsino, lcEndUpsino) ;
        and between(v.datinp, ldStartDate, ldEndDate) ;
	or l.custid = lcCustid and between(l.upsino, lcStartUpsino, lcEndUpsino) ;
	and between(l.puldat, ldStartDate, ldEndDate) ;
	order by v.upsino, v.datinp

* Custom method to get data from then drop the duplicated custid, upsino, and data fields.
thisform.mergefields('vl')


* Join the "vl" cursor and the DGA table into cursor "vld"
select * from vl v ;
	full outer join dga d on v.custid = d.custid and v.upsino = d.upsino and v.datinp = d.puldat ;
	into cursor vld readwrite ;
	where v.custid = lcCustid and between(v.upsino, lcStartUpsino, lcEndUpsino) ;
	and between(v.datinp, ldStartDate, ldEndDate) ;
	or d.custid = lcCustid and between(d.upsino, lcStartUpsino, lcEndUpsino) ;
	and between(d.puldat, ldStartDate, ldEndDate) ;
	order by v.upsino, v.datinp

* Custom method to get data from then drop the duplicated custid, upsino, and data fields.		
thisform.mergefields('vld')

Thank you again.