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Posted to commits@druid.apache.org by GitBox <gi...@apache.org> on 2021/08/12 23:10:17 UTC
[GitHub] [druid] paul-rogers opened a new issue #11586: Query with COUNT(*), nested sub-query returns no results.
paul-rogers opened a new issue #11586:
URL: https://github.com/apache/druid/issues/11586
### Affected Version
The Druid version where the problem was encountered.
### Description
Consider the "stock" Wikipedia data source and stock Docker Druid cluster. Version: 0.21.
The query is designed to identify the number of rows that would result from building a new roll-up table with just three of the dimensions:
```sql
SELECT COUNT(*)
FROM (
SELECT hr, channel, page, COUNT(*) AS cnt
FROM (
SELECT
DATE_TRUNC('hour', __time) AS hr,
channel,
page
FROM "wikiticker-2015-09-12-sampled"
)
GROUP BY hr, channel, page
)
```
The query returns zero rows.
However, replace the `count(*)` with `*` and we get many rows of results. (The rows give the expected number of rows per group in the new roll-up datasource.) Since a `SELECT *` query returns rows, expected the `COUNT(*)` to count those rows.
A workaround is to use the form which works, and to count the rows in the client.
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[GitHub] [druid] SharuBob commented on issue #11586: Query with COUNT(*), nested sub-query returns no results
Posted by GitBox <gi...@apache.org>.
SharuBob commented on issue #11586:
URL: https://github.com/apache/druid/issues/11586#issuecomment-899754077
@paul-rogers did you find any solution for the above issue. Looks like I have reported more or less same issue [here](https://github.com/apache/druid/issues/11603)
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[GitHub] [druid] paul-rogers commented on issue #11586: Query with COUNT(*), nested sub-query returns no results
Posted by GitBox <gi...@apache.org>.
paul-rogers commented on issue #11586:
URL: https://github.com/apache/druid/issues/11586#issuecomment-902295161
@SharuBob, thanks for pointing out the related issue. As it turns out, the query I'm using has no `HAVING` clause. In my case, the issue seems related to the nested queries. However, you may be right that both are symptoms of the same underlying issue, perhaps in the Calcite planner.
The solution I used is simply to omit the outer `COUNT(*)` and have the client do the counting. Doing so is inefficient, and may not scale to huge data sets. But, it was a quick & dirty work-around for my specific use case.
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[GitHub] [druid] kxbin edited a comment on issue #11586: Query with COUNT(*), nested sub-query returns no results
Posted by GitBox <gi...@apache.org>.
kxbin edited a comment on issue #11586:
URL: https://github.com/apache/druid/issues/11586#issuecomment-1017255778
**I found that if the dataset is 0 rows**
**The result of count(*) is not 0, but returned no data.**
druid version is 0.20.0
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[GitHub] [druid] SharuBob commented on issue #11586: Query with COUNT(*), nested sub-query returns no results
Posted by GitBox <gi...@apache.org>.
SharuBob commented on issue #11586:
URL: https://github.com/apache/druid/issues/11586#issuecomment-902451119
@paul-rogers Thank you for the reply again. Even I have made more or less same short term work around, will still use subquery to fetch one of the columns and then do the len(array) at client side to get the count.
Hope this will be addressed in the coming days. 🙏
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[GitHub] [druid] kxbin commented on issue #11586: Query with COUNT(*), nested sub-query returns no results
Posted by GitBox <gi...@apache.org>.
kxbin commented on issue #11586:
URL: https://github.com/apache/druid/issues/11586#issuecomment-1017255778
**I found that if the dataset is 0 rows**
**The result of count(*) is not 0, but returned no data.**
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