>lsqlstring = " SELECT Purchase.*, Accmst.accname, Depts.deptname;
> FROM purchase LEFT OUTER JOIN accmst;
> LEFT OUTER JOIN depts ;
> ON Purchase.department = Depts.deptno ;
> ON Purchase.partycode = Accmst.acccd"

The problem is that ONs are matched to JOINs from the inside out. So your query says to join accmst to depts based on the condition purchase.department = depts.deptno. Then, it should join that result to purchase based on Purchase.partycode=Accmst.acccd.

To solve this, you have some alternatives, but the simplest is to make Purchase the innermost table in the query. Rewrite the joins as:

FROM accmst LEFT OUTER JOIN depts
LEFT OUTER JOIN Purchase
ON Purchase.Department=Depts.Deptno
ON Purchase.Partycode=Accmst.acccd

Tamar