During customization I got requirement that in drop down or lookup shows those customer which did not have sales line.
I handle this customization with the help of no exist join. Code snippet is something like.
public void lookup()
{
Query query = new Query();
QueryBuildDataSource queryBuildDataSource, qbds, dsView;
QueryBuildRange queryBuildRange;
SysTableLookup sysTableLookup = SysTableLookup::newParameters(tableNum(CustTable), this);
sysTableLookup.addLookupField(fieldNum(CustTable, AccountNum));
sysTableLookup.addLookupField(fieldNum(CustTable, Party), false);
queryBuildDataSource = query.addDataSource(tableNum(CustTable));
qbds = queryBuildDataSource.addDataSource(tableNum(DirPartyTable));
qbds.joinMode(JoinMode::InnerJoin);
qbds.addLink(fieldNum(CustTable, Party), fieldNum(DirPartyTable, RecId));
dsView =queryBuildDataSource.addDataSource(tableNum(SalesLine));
dsView.joinMode(JoinMode::NoExistsJoin);
dsView.addLink( fieldNum(Salesline, CustomerAccount),fieldNum(CustTable, AccountNum));
sysTableLookup.parmQuery(query);
sysTableLookup.performFormLookup();
}