GitHub user maropu opened a pull request:
https://github.com/apache/spark/pull/20166
[SPARK-22973][SQL] Fix incorrect results of Casting Map to String
## What changes were proposed in this pull request?
This pr fixed the issue when casting maps into strings;
```
scala> Seq(Map(1 -> "a", 2 -> "b")).toDF("a").write.saveAsTable("t")
scala> sql("SELECT cast(a as String) FROM t").show(false)
+----------------------------------------------------------------+
|a |
+----------------------------------------------------------------+
|org.apache.spark.sql.catalyst.expressions.UnsafeMapData@38bdd75d|
+----------------------------------------------------------------+
```
This pr modified the result into;
```
+----------------+
|a |
+----------------+
|[1 -> a, 2 -> b]|
+----------------+
```
## How was this patch tested?
Added tests in `CastSuite`.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/maropu/spark SPARK-22973
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/20166.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #20166
----
commit efc28e3aa2a0add8e325d60162090c9ee3fdfcba
Author: Takeshi Yamamuro <yamamuro@...>
Date: 2018-01-05T14:33:14Z
Cast maps to strings
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