maropu commented on a change in pull request #21479: [SPARK-23903][SQL] Add
support for date extract
URL: https://github.com/apache/spark/pull/21479#discussion_r409933251
##########
File path:
sql/catalyst/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBase.g4
##########
@@ -592,6 +592,7 @@ primaryExpression
| identifier
#columnReference
| base=primaryExpression '.' fieldName=identifier
#dereference
| '(' expression ')'
#parenthesizedExpression
+ | EXTRACT '(' field=identifier FROM source=valueExpression ')'
#extract
Review comment:
Ah, I see. Nice catch! The python script that we are now working on
(https://github.com/apache/spark/pull/28224) just dumps the entries of
`ExpressionDescription(ExpressionInfo)`, so the output unfortunately cannot
include a doc entry for `EXTRACT` now. To document it, there are the three
options that I can think of;
- (the simplest fix) Add some description about `EXTRACT` in the SELECT
syntax page (e.g., the `named_expression` section), then add a link to
`date_part` in the built-in function page.
- Add a dummy `ExpressionDescription` for `EXTRACT` like this;
```
@ExpressionDescription(
usage = "_FUNC_(field, source) - Extracts a part of the date/timestamp or
interval source.",
arguments = """ ... """,
examples = """
Examples:
> SELECT _FUNC_('YEAR' FROM TIMESTAMP '2019-08-12 01:00:00.123456');
2019
""",
since = "3.0.0")
case class Extract(...) extends DatePart(field, source, child)
```
- Add a new entry for an alias name in `ExpressionDescription` like this;
```
@ExpressionDescription(
usage = "_FUNC_(field, source) - Extracts a part of the date/timestamp or
interval source.",
arguments = """... """,
alias = "extract",
examples = """
Examples:
...
> SELECT _FUNC_ALIAS_('seconds' FROM interval 5 hours 30 seconds 1
milliseconds 1 microseconds);
30.001001
""",
since = "3.0.0")
case class DatePart(...) extends RuntimeReplaceable {
```
Which one is preferred, or any other smarter idea?
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