## What changes were proposed in this pull request?
When we use upper case partition name in Hive table, like:
```
CREATE TABLE src (KEY STRING, VALUE STRING) PARTITIONED BY (DS STRING)
```
Then, `insert into table` query doesn't work
```
INSERT INTO TABLE src PARTITION(ds) SELECT 'k' key, 'v' value, '1' ds
// or
INSERT INTO TABLE src PARTITION(DS) SELECT 'k' KEY, 'v' VALUE, '1' DS
```
```
[info] org.apache.spark.sql.AnalysisException:
org.apache.hadoop.hive.ql.metadata.Table.ValidationFailureSemanticException: Partition spec {ds=, DS=1} contains non-partition columns;
```
As Hive metastore is not case preserving and keeps partition columns with lower cased names, we lowercase column names in partition spec before passing to Hive client. But we write upper case column names in partition paths.
However, when calling `loadDynamicPartitions` to do `insert into table` for dynamic partition, Hive calculates full path spec for partition paths. So it calculates a partition spec like `{ds=, DS=1}` in above case and fails partition column validation. This patch is proposed to fix the issue by lowercasing the column names in written partition paths for Hive partitioned table.
This fix touchs `saveAsHiveFile` method, which is used in `InsertIntoHiveDirCommand` and `InsertIntoHiveTable` commands. Among them, only `InsertIntoHiveTable` passes `partitionAttributes` parameter. So I think this change only affects `InsertIntoHiveTable` command.
## How was this patch tested?
Added test.
Closes#24886 from viirya/SPARK-28054.
Authored-by: Liang-Chi Hsieh <viirya@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
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