[GitHub] [spark] dongjoon-hyun commented on a change in pull request #27580: [SPARK-27619][SQL]MapType should be prohibited in hash expressions

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dongjoon-hyun commented on a change in pull request #27580: [SPARK-27619][SQL]MapType should be prohibited in hash expressions
URL: https://github.com/apache/spark/pull/27580#discussion_r384915364
 
 

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 File path: docs/sql-migration-guide.md
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 @@ -224,6 +224,8 @@ license: |
 
   - Since Spark 3.0, when casting string value to integral types(tinyint, smallint, int and bigint), datetime types(date, timestamp and interval) and boolean type, the leading and trailing whitespaces (<= ASCII 32) will be trimmed before converted to these type values, e.g. `cast(' 1\t' as int)` results `1`, `cast(' 1\t' as boolean)` results `true`, `cast('2019-10-10\t as date)` results the date value `2019-10-10`. In Spark version 2.4 and earlier, while casting string to integrals and booleans, it will not trim the whitespaces from both ends, the foregoing results will be `null`, while to datetimes, only the trailing spaces (= ASCII 32) will be removed.
 
+  - Since Spark 3.0, An analysis exception will be thrown when hash expressions are applied on elements of MapType. To restore the behavior before Spark 3.0, set `spark.sql.legacy.useHashOnMapType` to true.
 
 Review comment:
   nit.
   ```
   `An` -> `an`
   to true -> to `true`
   ```

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