ektravel commented on code in PR #12549: URL: https://github.com/apache/druid/pull/12549#discussion_r1117383500
########## docs/querying/sql-data-types.md: ########## @@ -85,8 +87,45 @@ the `UNNEST` functionality available in some other SQL dialects. Refer to the do > they are handled in Druid SQL and in native queries. For example, > expressions involving multi-value dimensions may be > incorrectly optimized by the Druid SQL planner: `multi_val_dim = 'a' AND > multi_val_dim = 'b'` is optimized to > `false`, even though it is possible for a single row to have both "a" and > "b" as values for `multi_val_dim`. The -> SQL behavior of multi-value dimensions will change in a future release to more closely align with their behavior -> in native queries. +> SQL behavior of multi-value dimensions may change in a future release to more closely align with their behavior +> in native queries, but the [multi-value string functions](./sql-multivalue-string-functions.md) should be able to provide +> nearly all possible native functionality. + +## Arrays +Druid supports `ARRAY` types constructed at query time, though it currently lacks the ability to store them in +segments. `ARRAY` types behave as standard SQL arrays, where results are grouped by matching entire arrays. This is in +contrast to the implicit `UNNEST` that occurs when grouping on multi-value dimensions directly or when used with the +multi-value functions. You can convert multi-value dimensions to standard SQL arrays either by explicitly converting +them with `MV_TO_ARRAY`, or implicitly when used within the [array functions](./sql-array-functions.md). Arrays may +also be constructed from multiple columns using the array functions. + +## Multi-value strings behavior +The behavior of Druid [multi-value string dimensions](multi-value-dimensions.md) varies depending on the context of their usage. + +When used with standard `VARCHAR` functions, which expect a single input value per row, Druid maps the function across all values in the row. +the function across all values in the row. If the row is null or empty, the function will recieve `NULL` as its input, Review Comment: Try to avoid future tense when possible. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
