Cannot select fields when selecting multiple aggregates in outer query

[kostasb]

v1.2.3

When selecting a field or tag along with multiple aggregate fields in the outer query, an error ERR: cannot select fields when selecting multiple aggregates is returned.

Repro:

> insert test,if=AGG1 input=1,output=2,speed=3
> insert test,if=AGG2 input=4,output=5,speed=6

> select I,O from (select max(input) as I,max(output) as O,max(speed) as S from test where if =~ /^AGG/ group by if)
name: test
time I O
---- - -
0    1 2
0    4 5

> select I,O,if from (select max(input) as I,max(output) as O,max(speed) as S from test where if =~ /^AGG/ group by if)
ERR: cannot select fields when selecting multiple aggregates

> select I,if from (select percentile("input",95) as I,percentile("output",95) as O,percentile("speed",95) as S from test where if =~ /^AGG/ group by if)
name: test
time                I if
----                - --
1493130907774306331 1 AGG1
1493130926117777461 4 AGG2

> select I,O,if from (select percentile("input",95) as I,percentile("output",95) as O,percentile("speed",95) as S from test where if =~ /^AGG/ group by if)
ERR: cannot select fields when selecting multiple aggregates

Works well without aggregates:

> select I,O,if from (select "input" as I,"output" as O,"speed" as S from test where if =~ /^AGG/ group by if)
name: test
time                I O if
----                - - --
1493130907774306331 1 2 AGG1
1493130926117777461 4 5 AGG2

[jsternberg]

@benbjohnson says that #8081 fixes this.