How to find rows in one table that have no corresponding row in another table

Question

I have a 1:1 relationship between two tables. I want to find all the rows in table A that don\'t have a corresponding row in table B. I use this query:

SELEC         


        

Answer 1

You have to check every ID in tableA against every ID in tableB. A fully featured RDBMS (such as Oracle) would be able to optimize that into an INDEX FULL FAST SCAN and not touch the table at all. I don't know whether H2's optimizer is as smart as that.

H2 does support the MINUS syntax so you should try this

select id from tableA
minus
select id from tableB
order by id desc

That may perform faster; it is certainly worth benchmarking.