AlterQuery  prewhere_column_missing (children 2)
 ExpressionList (children 1)
  AlterCommand ADD_COLUMN (children 1)
   ColumnDeclaration hash_x (children 2)
    DataType UInt64
    Function intHash64 (children 1)
     ExpressionList (children 1)
      Identifier x
 Identifier prewhere_column_missing