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From alin-corodescu <alin.corode...@gmail.com>
Subject Incorrect map query built when joining with a subquery with group by statement
Date Fri, 27 Oct 2017 12:32:24 GMT

While experimenting around with Ignite, I came across a bug regarding the
map query building. (the queries that run on each individual node). Consider
the following dummy query (this is a reproduction of the error I found while
testing actual production queries):

SELECT t1.name, count(1)
FROM "default".Persons t1
 JOIN (SELECT name from "default".Persons group by name) t2
 on t1.name = t2.name
 group by t1.name

This query cannot be run on nodes because of how the map query is built. 
When using explain for this query, the first line, which represents the map
query to be run on remote nodes, looks like this :

    T1__Z0.NAME AS __C0_0,
    COUNT(1) AS __C0_1
FROM "default".PERSONS T1__Z0
    /* "default".PERSONS.__SCAN_ */

which is obviously an incorrect SQL query, as there an aggregation function
called without a group by clause. Thus, on each remote node, the following
exception will be thrown:

Caused by: org.h2.jdbc.JdbcSQLException: Column "T1__Z0.NAME" must be in the
GROUP BY list; SQL statement

 This is only happening (as far as I observed) only when joining with a
subquery containing a group by clause, and the error can be reproduced with
virtually any table. Has anyone else discovered encountered this behaviour

As a side note, enabling an index on the "name" column seems to overcome the
problem, but it is not a viable solution for production systems with many
different queries.


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