Github user lins05 commented on a diff in the pull request:
https://github.com/apache/spark/pull/15487#discussion_r83551685
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/Last.scala
---
@@ -29,15 +29,18 @@ import org.apache.spark.sql.types._
* a single partition, and we use a single reducer to do the aggregation.).
*/
@ExpressionDescription(
- usage = "_FUNC_(expr,isIgnoreNull) - Returns the last value of `child`
for a group of rows.")
+ usage = """_FUNC_(expr,isIgnoreNull) - Returns the last value of `child`
for a group of rows.
+ _FUNC_(expr,isIgnoreNull=false) - Returns the last value of `child`
for a group of rows.
--- End diff --
@hvanhovell @HyukjinKwon Thanks for the review. I'm simply following the
usage string of other functions, e.g:
```
spark-sql> describe function first;
Function: first
Class: org.apache.spark.sql.catalyst.expressions.aggregate.First
Usage: first(expr) - Returns the first value of `child` for a group of rows.
first(expr,isIgnoreNull=false) - Returns the first value of `child` for
a group of rows.
If isIgnoreNull is true, returns only non-null values.
spark-sql> describe function approx_count_distinct;
Function: approx_count_distinct
Class:
org.apache.spark.sql.catalyst.expressions.aggregate.HyperLogLogPlusPlus
Usage: approx_count_distinct(expr) - Returns the estimated cardinality by
HyperLogLog++.
approx_count_distinct(expr, relativeSD=0.05) - Returns the estimated
cardinality by HyperLogLog++
with relativeSD, the maximum estimation error allowed.
```
So it seems the current convention is that: the first line is a short
one-line description, followed by a detail description. Do we have any explicit
"usage string style" to follow?
@hvanhovell I'll add the note about nondeterministic.
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