AlterQuery  nullable_alter (children 2)
 ExpressionList (children 1)
  AlterCommand MODIFY_COLUMN (children 1)
   ColumnDeclaration x (children 1)
    DataType Nullable (children 1)
     ExpressionList (children 1)
      DataType FixedString (children 1)
       ExpressionList (children 1)
        Literal UInt64_5
 Identifier nullable_alter