AlterQuery  agg_func_col (children 2)
 ExpressionList (children 1)
  AlterCommand ADD_COLUMN (children 1)
   ColumnDeclaration af_avg1 (children 1)
    DataType AggregateFunction (children 1)
     ExpressionList (children 2)
      Identifier avg
      DataType UInt8
 Identifier agg_func_col
