Dongjoon Hyun
142df4834b
[SPARK-16429][SQL] Include StringType columns in describe()
## What changes were proposed in this pull request?
Currently, Spark `describe` supports `StringType`. However, `describe()` returns a dataset for only all numeric columns. This PR aims to include `StringType` columns in `describe()`, `describe` without argument.
**Background**
```scala
scala> spark.read.json("examples/src/main/resources/people.json").describe("age", "name").show()
+-------+------------------+-------+
|summary| age| name|
+-------+------------------+-------+
| count| 2| 3|
| mean| 24.5| null|
| stddev|7.7781745930520225| null|
| min| 19| Andy|
| max| 30|Michael|
+-------+------------------+-------+
```
**Before**
```scala
scala> spark.read.json("examples/src/main/resources/people.json").describe().show()
+-------+------------------+
|summary| age|
+-------+------------------+
| count| 2|
| mean| 24.5|
| stddev|7.7781745930520225|
| min| 19|
| max| 30|
+-------+------------------+
```
**After**
```scala
scala> spark.read.json("examples/src/main/resources/people.json").describe().show()
+-------+------------------+-------+
|summary| age| name|
+-------+------------------+-------+
| count| 2| 3|
| mean| 24.5| null|
| stddev|7.7781745930520225| null|
| min| 19| Andy|
| max| 30|Michael|
+-------+------------------+-------+
```
## How was this patch tested?
Pass the Jenkins with a update testcase.
Author: Dongjoon Hyun <dongjoon@apache.org>
Closes #14095 from dongjoon-hyun/SPARK-16429.