Strange negative results in select Queries

Problem

I lately ran into problems that a select returned an unexpected negative results und certain condions, e.g. I expected 1 but it returned -1.

select --
       1
  from dual;

Reason

It turns out that this is a behaviour seen only in clients using SQLPlus or the same libraries as SQLPlus or something of the sort. From https://docs.oracle.com/en/database/oracle/oracle-database/19/sqpug/REMARK.html

A "–" at the end of a REMARK line is treated as a line continuation character.

To me, this is a flaw in the SQLPlus design as, to the best of my knowledge, the SQL standard does not inhibt empty line comments or defines a line continuation character (like \ in bash, if after \ there immediately follows line break). It is even worse as it does not work consistently this way. The following should, if - is line continuation character, throw a syntax error at both instances of the -- but works perfectly fine.

--
select 1
  from --
  dual;

Solution

Do not use empty line comments. Place at least one none whitespace character behind the --.