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Posted to commits@druid.apache.org by GitBox <gi...@apache.org> on 2022/09/20 08:52:06 UTC
[GitHub] [druid] hosswald opened a new pull request, #13128: Clarified the behaviour of COUNT(DISTINCT column) on multi-value columns
hosswald opened a new pull request, #13128:
URL: https://github.com/apache/druid/pull/13128
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It was unclear to me how COUNT(DISTINCT column) behaved for multi-value columns, and I found the docs unhelpful in that regard, so I clarified it.
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[GitHub] [druid] kfaraz commented on pull request #13128: Clarified the behaviour of SQL COUNT(DISTINCT dim) on multi-value dimensions
Posted by GitBox <gi...@apache.org>.
kfaraz commented on PR #13128:
URL: https://github.com/apache/druid/pull/13128#issuecomment-1252151086
Thanks for your first PR, @hosswald !
I think we should also add an entry to the table on the doc page that talks about "SQL multi-value string functions".
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[GitHub] [druid] vogievetsky merged pull request #13128: Clarified the behaviour of SQL COUNT(DISTINCT dim) on multi-value dimensions
Posted by GitBox <gi...@apache.org>.
vogievetsky merged PR #13128:
URL: https://github.com/apache/druid/pull/13128
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[GitHub] [druid] techdocsmith commented on a diff in pull request #13128: Clarified the behaviour of SQL COUNT(DISTINCT dim) on multi-value dimensions
Posted by GitBox <gi...@apache.org>.
techdocsmith commented on code in PR #13128:
URL: https://github.com/apache/druid/pull/13128#discussion_r975870723
##########
docs/querying/sql-aggregations.md:
##########
@@ -66,7 +66,7 @@ In the aggregation functions supported by Druid, only `COUNT`, `ARRAY_AGG`, and
|Function|Notes|Default|
|--------|-----|-------|
|`COUNT(*)`|Counts the number of rows.|`0`|
-|`COUNT(DISTINCT expr)`|Counts distinct values of `expr`.<br /><br />When `useApproximateCountDistinct` is set to "true" (the default), this is an alias for `APPROX_COUNT_DISTINCT`. The specific algorithm depends on the value of [`druid.sql.approxCountDistinct.function`](../configuration/index.md#sql). In this mode, you can use strings, numbers, or prebuilt sketches. If counting prebuilt sketches, the prebuilt sketch type must match the selected algorithm.<br /><br />When `useApproximateCountDistinct` is set to "false", the computation will be exact. In this case, `expr` must be string or numeric, since exact counts are not possible using prebuilt sketches. In exact mode, only one distinct count per query is permitted unless `useGroupingSetForExactDistinct` is enabled.|`0`|
+|`COUNT(DISTINCT expr)`|Counts distinct values of `expr`.<br /><br />When `useApproximateCountDistinct` is set to "true" (the default), this is an alias for `APPROX_COUNT_DISTINCT`. The specific algorithm depends on the value of [`druid.sql.approxCountDistinct.function`](../configuration/index.md#sql). In this mode, you can use strings, numbers, or prebuilt sketches. If counting prebuilt sketches, the prebuilt sketch type must match the selected algorithm.<br /><br />When `useApproximateCountDistinct` is set to "false", the computation will be exact. In this case, `expr` must be string or numeric, since exact counts are not possible using prebuilt sketches. In exact mode, only one distinct count per query is permitted unless `useGroupingSetForExactDistinct` is enabled.<br /><br />Will count each distinct value in a [`multi-value`](../querying/multi-value-dimensions.md)-row seperately.|`0`|
Review Comment:
```suggestion
|`COUNT(DISTINCT expr)`|Counts distinct values of `expr`.<br /><br />When `useApproximateCountDistinct` is set to "true" (the default), this is an alias for `APPROX_COUNT_DISTINCT`. The specific algorithm depends on the value of [`druid.sql.approxCountDistinct.function`](../configuration/index.md#sql). In this mode, you can use strings, numbers, or prebuilt sketches. If counting prebuilt sketches, the prebuilt sketch type must match the selected algorithm.<br /><br />When `useApproximateCountDistinct` is set to "false", the computation will be exact. In this case, `expr` must be string or numeric, since exact counts are not possible using prebuilt sketches. In exact mode, only one distinct count per query is permitted unless `useGroupingSetForExactDistinct` is enabled.<br /><br />Counts each distinct value in a [`multi-value`](../querying/multi-value-dimensions.md)-row separately.|`0`|
```
Thanks for contributing, @hosswald ! My suggestion fixes a typo + avoids future tense
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