The approach you are suggesting will be very complex for current implementation. Also most probably very inefficient.
Actually I was thinking about another but similar approach: in many cases we can rewrite a subquery in WHERE clause into JOIN subquery. Like the following: SELECT x.* FROM x WHERE x.a = (SELECT MAX(y.a) FROM y WHERE y.b = x.b) ===> SELECT x.* FROM x, (SELECT MAX(y.a), y.b FROM y GROUP BY y.b) z WHERE x.b = z.b There are still problems here: 1. We will not be able to rewrite all the queries. 2. We should not rewrite queries like this by default because this will have a noticeable performance penalty for correctly collocated subqueries. Probably we will need some flag for that. Sergi 2017-05-31 21:26 GMT+03:00 Dmitriy Setrakyan <dsetrak...@apache.org>: > Igniters (specifically Sergi), > > It has come to my attention today that nested sub-select statements, when > used in combination with non-collocated joins do not work properly in > Ignite. > > So a query like this, where A, B, and C are all stored in Partitioned > caches and are **not** collocated at all, will not work. > > > > *select * from A, B where a.id <http://a.id> = b.a_id and b.somefield in > > (select somefield from C where c.zipcode = ?)* > > > The main reason it is not supported right now is because, in the absence of > collocation, such query may create N^N complexity and it was decided that > it is best not supporting it at all. > > However, I am not sure why N^N complexity is required. Why not support it > as follows? > > 1. execute the nested subquery and store the result in a temporary > Replicated table. > 2. execute the original query and use the temporary Replicated table > instead of the sub-query. > > Sergi, given that you are the author of the code, can you provide some > insight here? > > Thanks, > D. >
