Incorrect result in JDBC connectors when aggregation result is pruned away

[Yao-MR-zz]

the result of the sql is wrong,

JDBC Connector do not applyAggregation correctly for the case when the aggregates is empty and groupingSets is empty

source 1:
sql: select count(*) from mysql.test.userdata

source 2:
sql: select count(*) from mysql.test.userdata1

source 3:
sql: select count(*) from mysql.test.userdata2

Union sql:
select count() from (
-> select count() from mysql.test.userdata union all
-> select count() from mysql.test.userdata1 union all
-> select count() from mysql.test.userdata2
-> ) t;

absolute the result of Union sql is wrong，the right result should be 3

[findepi]

Thanks for a very good bug report @Yao-MR .

[findepi]

An even simpler repro case

SELECT 42 FROM (SELECT count(*) FROM nation)