count(distinct const) is incorrect

[pkommoju]

select sum(1), avg(2), min(3), max(4), count(5), count(distinct 6), stddev_samp(7.38) from a

should return
3,2,3,4,3,1,0

instead the actual result is
3,2,3,4,3,3,0

[zhouqingqing]

We don't support agg（distinct）yet.