Possible bug with count(distinct)

[aetter]

Originally reported as opendistro/for-elasticsearch-docs#221

select distinct host.name from metricbeat where `@timestamp` > '2020-04-29T06:12:34.352Z'  

return 7 rows:

{
"schema": [
{
"name": "host.name",
"type": "keyword"
}
],
"total": 7,
"datarows": [
[
"xxxxx"
]
,
[
"xxxxx"
]
,
[
"xxxxx"
]
,
[
"xxxxx"
]
,
[
"xxxxx"
]
,
[
"xxxxx"
]
,
[
"xxxxx"
]
],
"size": 7,
"status": 200
}

select count( distinct host.name ) as hostcount from metricbeat where `@timestamp` > '2020-04-29T06:12:34.352Z'  

return 0

[penghuo]

duplicate with #448? It has been fixed.