liukun4515 commented on a change in pull request #1991:
URL: https://github.com/apache/arrow-datafusion/pull/1991#discussion_r824737187
##########
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.
+ - `year`
+ - `EXTRACT(year FROM to_timestamp('2020-09-08T12:00:00+00:00')) -> 2020`
+ - `month`
+ - `EXTRACT(month FROM to_timestamp('2020-09-08T12:00:00+00:00')) -> 9`
+ - `week`
+ - `EXTRACT(week FROM to_timestamp('2020-09-08T12:00:00+00:00')) -> 23`
+ - `day`
+ - `EXTRACT(day FROM to_timestamp('2020-09-08T12:00:00+00:00')) -> 8`
+ - `hour`
+ - `EXTRACT(hour FROM to_timestamp('2020-09-08T12:00:00+00:00')) -> 12`
+ - `minute`
+ - `EXTRACT(minute FROM to_timestamp('2020-09-08T12:01:00+00:00')) -> 1`
+ - `second`
+ - `EXTRACT(second FROM to_timestamp('2020-09-08T12:00:03+00:00')) -> 3`
Review comment:
```suggestion
- `year`: EXTRACT(year FROM to_timestamp('2020-09-08T12:00:00+00:00')) ->
2020
- `month`: EXTRACT(month FROM to_timestamp('2020-09-08T12:00:00+00:00'))
-> 9
- `week`: EXTRACT(week FROM to_timestamp('2020-09-08T12:00:00+00:00')) ->
23
- `day`: EXTRACT(day FROM to_timestamp('2020-09-08T12:00:00+00:00')) -> 8
- `hour`: EXTRACT(hour FROM to_timestamp('2020-09-08T12:00:00+00:00')) ->
12
- `minute`: EXTRACT(minute FROM to_timestamp('2020-09-08T12:01:00+00:00'))
-> 1
- `second`: EXTRACT(second FROM to_timestamp('2020-09-08T12:00:03+00:00'))
-> 3
```
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