Re: [PR] [SPARK-23890][SQL] Support DDL for adding nested columns to struct types [spark]

["ottomata (via GitHub)" <gi...@apache.org>]

ottomata commented on PR #21012:
URL: https://github.com/apache/spark/pull/21012#issuecomment-1874135870

   Ah, sorry, my scala goggles weren't on quite right.  According to `verifyAlterTableAddColumn`, e.g. JsonDataSourceV2 is supported for ALTER TABLE ADD COLUMN.  We don't need to change that check at all.
   
   What we need to change is the check in ResolveCatalogSession that does
   ```scala
   throw QueryCompilationErrors.unsupportedTableOperationError(ident, "ADD COLUMN with qualified column")
   ```
   
   `if c.name.length > 1`.  
   However, if I remove that, I can see a problem in the way `AlterTableAddColumnsCommand` is implemented: it takes a `Seq[StructField]` as the list of columns to add.  This list is constructed by `convertToStructField` in ResolveSessionCatalog, which naively assumes that the col to add is not nested: 
   ```scala
       StructField(col.name.head, col.dataType, nullable = true, builder.build())
   ```
   Returns a StructField with the top level column name but the nested leaf column's DataType.
   
   
    


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