Github user xuanyuanking commented on a diff in the pull request:
https://github.com/apache/spark/pull/19773#discussion_r216600156
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala ---
@@ -350,16 +366,11 @@ case class AlterTableChangeColumnCommand(
s"${schema.fieldNames.mkString("[`", "`, `", "`]")}"))
}
- // Add the comment to a column, if comment is empty, return the original
column.
- private def addComment(column: StructField, comment: Option[String]):
StructField = {
- comment.map(column.withComment(_)).getOrElse(column)
- }
-
--- End diff --
```
Although the query above doesn't work well, why do users change column
types?
```
As the scenario described above, user firstly use int but during some time
found here we need a Long, he can rewrite the new data as Long and load data to
new partitions. And if we not support the type change, user should do the table
recreate job for this type change work.
Yep, if not the binary file, the query works OK.
```
Logging initialized using configuration in
jar:file:/Users/XuanYuan/Source/hive/apache-hive-1.2.2-bin/lib/hive-common-1.2.2.jar!/hive-log4j.properties
hive> CREATE TABLE t(a INT, b STRING, c INT);
OK
Time taken: 2.576 seconds
hive> INSERT INTO t VALUES (1, 'a', 3);;
Query ID = XuanYuan_20180911164348_32238a6c-b0a4-4cfd-aa3d-00a7628031cf
Total jobs = 3
Launching Job 1 out of 3
Number of reduce tasks is set to 0 since there's no reduce operator
Job running in-process (local Hadoop)
2018-09-11 16:43:51,684 Stage-1 map = 100%, reduce = 0%
Ended Job = job_local1624238888_0001
Stage-4 is selected by condition resolver.
Stage-3 is filtered out by condition resolver.
Stage-5 is filtered out by condition resolver.
Moving data to:
file:/Users/XuanYuan/Source/hive/apache-hive-1.2.2-bin/warehouse/t/.hive-staging_hive_2018-09-11_16-43-48_117_2262603440504094412-1/-ext-10000
Loading data to table default.t
Table default.t stats: [numFiles=1, numRows=1, totalSize=6, rawDataSize=5]
MapReduce Jobs Launched:
Stage-Stage-1: HDFS Read: 0 HDFS Write: 0 SUCCESS
Total MapReduce CPU Time Spent: 0 msec
OK
Time taken: 4.025 seconds
hive> select * from t;;
OK
1 a 3
Time taken: 0.164 seconds, Fetched: 1 row(s)
hive> ALTER TABLE t CHANGE a a STRING;
OK
Time taken: 0.177 seconds
hive> select * from t;
OK
1 a 3
Time taken: 0.12 seconds, Fetched: 1 row(s)
hive> quit;
```
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