Github user anabranch commented on the issue:
https://github.com/apache/spark/pull/16138
@cloud-fan great questions.
I thought that was strange too. However this is the **current** behavior as
well as Java `SimpleDateFormat`'s behavior. I did not implement that logic.
For example, today:
```scala
spark.sql("""
SELECT
cast(
cast(
unix_timestamp('2016-30-12', 'yyyy-MM-dd')
as timestamp)
as date)
""").take(5)
// res4: Array[org.apache.spark.sql.Row] = Array([2018-06-12])
```
Which seems wrong to me, but that's the logic that exists. The issue seems
to be that unix_timestamp returns an incorrect value when it should just return
null. The source is the behavior of `SimpleDateFormat`.
```scala
scala> import java.text.SimpleDateFormat
// import java.text.SimpleDateFormat
scala> val x = new SimpleDateFormat("yyyy-MM-dd")
// x: java.text.SimpleDateFormat = java.text.SimpleDateFormat@f67a0200
scala> x.parse("2016-30-12")
// res5: java.util.Date = Tue Jun 12 00:00:00 PDT 2018
```
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