Topic: Exists under two or more tables
FB3. Here such request:
select a.sn_mdl from modul a where exists (select b.id_ums from umass b inner join defect c on c.id_ums=b.id_ums where b.id_mdl=a.id_mdl )
What is necessary? It is necessary to receive all records in the table modul which have records in the table defect. The request fulfills correctly, but long. If in exists to leave one table umass, behavior exists expected (it is read on one record from umass for each record modul). If in exists two tables umass all is read. Generally tables umass and defect the big. Therefore it would be desirable such behavior - we read record from modul, we read sequentially umass and defect if record is we pass to other record modul. Whether It is possible to make something with exists? Or to look at other techniques? What?