johanl-db commented on code in PR #46734:
URL: https://github.com/apache/spark/pull/46734#discussion_r1613401422
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sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala:
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@@ -396,8 +396,9 @@ case class AlterTableChangeColumnCommand(
val newDataSchema = table.dataSchema.fields.map { field =>
if (field.name == originColumn.name) {
// Create a new column from the origin column with the new comment.
+ val newField = field.copy(dataType = newColumn.dataType)
Review Comment:
Can you make it more explicit that we effectively allow the data type to
change now but we only allow type changes that differ by collation?
E.g. by splitting `columnEqual` into checking that names match on one side
and that the type change is supported on the other + add a ` withNewType`
method.
##########
sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala:
##########
@@ -396,8 +396,9 @@ case class AlterTableChangeColumnCommand(
val newDataSchema = table.dataSchema.fields.map { field =>
if (field.name == originColumn.name) {
// Create a new column from the origin column with the new comment.
+ val newField = field.copy(dataType = newColumn.dataType)
Review Comment:
Lines 359-367: the comment needs to be updated to be clear we now allow
changing collation.
Side note: it gives the hive-style syntax for ALTER COLUMN but that's only
one of the two syntaxes, see:
https://github.com/apache/spark/blob/master/sql/api/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBaseParser.g4#L130
The other one is the one (partially) documented and the more
capable/preferred one:
https://spark.apache.org/docs/3.5.1/sql-ref-syntax-ddl-alter-table.html#parameters-4
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