Github user maropu commented on a diff in the pull request:
https://github.com/apache/spark/pull/19773#discussion_r216123860
--- 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 --
Ah, ok. Thanks for the check. btw, have you checked if this could work
correctly?
```
sql("""CREATE TABLE t(a INT, b STRING, c INT) using parquet""")
sql("""INSERT INTO t VALUES (1, 'a', 3)""")
sql("""ALTER TABLE t CHANGE a a STRING""")
spark.table("t").show
org.apache.spark.sql.execution.QueryExecutionException: Parquet column
cannot be converted in file
file:///Users/maropu/Repositories/spark/spark-master/spark-warehouse/t/part-00000-93ddfd05-690a-480c-8cc5-fd0981206fc3-c000.snappy.parquet.
Column: [a], Expected: string, Found: INT32
at
org.apache.spark.sql.execution.datasources.FileScanRDD$$anon$1.nextIterator(FileScanRDD.scala:192)
at
org.apache.spark.sql.execution.datasources.FileScanRDD$$anon$1.hasNext(FileScanRDD.scala:109)
at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage1.scan_nextBatch_0$(Unknown
Source)
at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage1.processNext(Unknown
Source)
at org.apache.spark.s
...
```
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