gatorsmile commented on a change in pull request #24780:
[SPARK-26388][SQL][WIP]_implement_hive_ddl_alter_table_replace_columns
URL: https://github.com/apache/spark/pull/24780#discussion_r290810958
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File path:
sql/catalyst/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBase.g4
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@@ -115,6 +115,8 @@ statement
(identifier | FOR COLUMNS identifierSeq | FOR ALL COLUMNS)? #analyze
| ALTER TABLE tableIdentifier
ADD COLUMNS '(' columns=colTypeList ')'
#addTableColumns
+ | ALTER TABLE tableIdentifier
+ REPLACE COLUMNS '(' columns=colTypeList ')'
#replaceTableColumns
Review comment:
Let me give a typical scenario. For an existing table, if we drop the column
`col1`, the data will not be visible to the end users. This is expected.
However, if we add `col1` back, the previous values of the column `col1` should
not be visible to the end users too. This is how the other database systems
work. What is your thought?
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