[GitHub] [druid] clintropolis commented on a change in pull request #12226: array_concat_agg and array_agg support for array inputs

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clintropolis commented on a change in pull request #12226:
URL: https://github.com/apache/druid/pull/12226#discussion_r799908259



##########
File path: docs/querying/sql.md
##########
@@ -376,9 +376,11 @@ In the aggregation functions supported by Druid, only `COUNT`, `ARRAY_AGG`, and
 |`ANY_VALUE(expr, maxBytesPerString)`|Like `ANY_VALUE(expr)`, but for strings. The `maxBytesPerString` parameter determines how much aggregation space to allocate per string. Strings longer than this limit will be truncated. This parameter should be set as low as possible, since high values will lead to wasted memory.|`null` if `druid.generic.useDefaultValueForNull=false`, otherwise `''`|
 |`GROUPING(expr, expr...)`|Returns a number to indicate which groupBy dimension is included in a row, when using `GROUPING SETS`. Refer to [additional documentation](aggregations.md#grouping-aggregator) on how to infer this number.|N/A|
 |`ARRAY_AGG(expr, [size])`|Collects all values of `expr` into an ARRAY, including null values, with `size` in bytes limit on aggregation size (default of 1024 bytes). If the aggregated array grows larger than the maximum size in bytes, the query will fail. Use of `ORDER BY` within the `ARRAY_AGG` expression is not currently supported, and the ordering of results within the output array may vary depending on processing order.|`null`|
-|`ARRAY_AGG(DISTINCT expr, [size])`|Collects all distinct values of `expr` into an ARRAY, including null values, with `size` in bytes limit on aggregation size (default of 1024 bytes) per aggregate. If the aggregated array grows larger than the maximum size in bytes, the query will fail. Use of `ORDER BY` within the `ARRAY_AGG` expression is not currently supported, and the ordering of results within the output array may vary depending on processing order.|`null`|
+|`ARRAY_AGG(DISTINCT expr, [size])`|Collects all distinct values of `expr` into an ARRAY, including null values, with `size` in bytes limit on aggregation size (default of 1024 bytes) per aggregate. If the aggregated array grows larger than the maximum size in bytes, the query will fail. Use of `ORDER BY` within the `ARRAY_AGG` expression is not currently supported, and the ordering of results will be based on the default for the element type.|`null`|
+|`ARRAY_CONCAT_AGG(expr, [size])`|Concatenates all array `expr` into a single ARRAY, with `size` in bytes limit on aggregation size (default of 1024 bytes).   Input `expr` _must_ be an array. Null `expr` will be ignored, but any null values within an `expr` _will_ be included in the resulting array. If the aggregated array grows larger than the maximum size in bytes, the query will fail. Use of `ORDER BY` within the `ARRAY_CONCAT_AGG` expression is not currently supported, and the ordering of results within the output array may vary depending on processing order.|`null`|

Review comment:
       i agree for sure, I'm planning on starting to revamp the arrays documentation, but don't really want to do it in this PR
   
   I haven't put together any examples yet, but agree that would be very nice




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