clintropolis commented on a change in pull request #11254:
URL: https://github.com/apache/druid/pull/11254#discussion_r632837576
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File path: docs/misc/math-expr.md
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@@ -50,7 +50,7 @@ Expressions can contain variables. Variable names may contain
letters, digits, '
For logical operators, a number is true if and only if it is positive (0 or
negative value means false). For string type, it's the evaluation result of
'Boolean.valueOf(string)'.
-[Multi-value string dimensions](../querying/multi-value-dimensions.md) are
supported and may be treated as either scalar or array typed values. When
treated as a scalar type, an expression will automatically be transformed to
apply the scalar operation across all values of the multi-valued type, to mimic
Druid's native behavior. Values that result in arrays will be coerced back into
the native Druid string type for aggregation. Druid aggregations on multi-value
string dimensions on the individual values, _not_ the 'array', behaving similar
to the `UNNEST` operator available in many SQL dialects. However, by using the
`array_to_string` function, aggregations may be done on a stringified version
of the complete array, allowing the complete row to be preserved. Using
`string_to_array` in an expression post-aggregator, allows transforming the
stringified dimension back into the true native array type.
+[Multi-value string dimensions](../querying/multi-value-dimensions.md) are
supported and may be treated as either scalar or array typed values. When
treated as a scalar type, an expression will automatically be transformed to
apply the scalar operation across all values of the multi-valued type, to mimic
Druid's native behavior. Values that result in arrays will be coerced back into
the native Druid string type for aggregation. Druid aggregations on multi-value
string dimensions act on the individual values, _not_ the 'array', behaving
similar to the `UNNEST` operator available in many SQL dialects. However, by
using the `array_to_string` function, aggregations may be done on a stringified
version of the complete array, allowing the complete row to be preserved. Using
`string_to_array` in an expression post-aggregator, allows transforming the
stringified dimension back into the true native array type.
Review comment:
Oh man, no idea why I worded this so strange back in #7588.. i wonder if
something like this would be a bit clearer:
> Values that result in arrays will be coerced back into the native Druid
string type for grouping and aggregation. Grouping on multi-value string
dimensions in Druid will group by the individual values, _not_ the 'array',
behaving similar to the `UNNEST` operator available in many SQL dialects.
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