[GitHub] [arrow-datafusion] Ted-Jiang commented on a change in pull request #1991: Add doc for EXTRACT, date_part

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Ted-Jiang commented on a change in pull request #1991:
URL: https://github.com/apache/arrow-datafusion/pull/1991#discussion_r825776860



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File path: docs/source/user-guide/sql/datafusion-functions.md
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@@ -84,3 +84,31 @@ Note that `CAST(.. AS Timestamp)` converts to Timestamps with Nanosecond resolut
 - Other Timestamp() columns or values
 
 Note that `CAST(.. AS Timestamp)` converts to Timestamps with Nanosecond resolution; this function is the only way to convert/cast to seconds resolution.
+
+## `EXTRACT, date_part`
+
+`EXTRACT(field FROM source)`
+
+- The extract function retrieves subfields such as year or hour from date/time values.
+  source must be a value expression of type timestamp, Data32, Data64 field is an identifier that selects what field to extract from the source value.
+  The extract function returns values of type u32.

Review comment:
       @liukun4515 We need  a discussion  about wether need support negative `timestamp `or `date`




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