[GitHub] spark pull request #15230: [SPARK-17657] [SQL] Disallow Users to Change Tabl...

[gatorsmile <gi...@git.apache.org>]

Github user gatorsmile commented on a diff in the pull request:

    https://github.com/apache/spark/pull/15230#discussion_r82940270
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala ---
    @@ -225,6 +225,11 @@ case class AlterTableSetPropertiesCommand(
         val catalog = sparkSession.sessionState.catalog
         val table = catalog.getTableMetadata(tableName)
         DDLUtils.verifyAlterTableType(catalog, table, isView)
    +    // Not allowed to switch the table type.
    +    if (properties.contains("EXTERNAL")) {
    --- End diff --
    
    This is officially documented in the Hive document, as shown in the [link](https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL):
    `TBLPROPERTIES ("EXTERNAL"="TRUE") in release 0.6.0+ (HIVE-1329) \u2013 Change a managed table to an external table and vice versa for "FALSE".`
    
    This is the only property users are not allowed to change. The other Hive-specific properties are still allowed to change, because Hive also allows it. 
    
    For the our Spark-reserved properties, users are not allowed to change. See the function call `verifyTableProperties` in `[alterTable](https://github.com/apache/spark/blob/b9a147181d5e38d9abed0c7215f4c5cb695f579c/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveExternalCatalog.scala#L393)`. 


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