Not showing error in dual while using it as arithmetic expression

Question

Hi,
I have a requirement to throw error if two consecutive numbers or two consecutive operators are given. For this I would like to use dual table.
It is throwing error if two numbers are given, but not throwing error if it has two operators.
Error thrown for -> select 2 4 - 7 from dual;
Error not thrown for -> select 2 + - 7 from dual;
or
select 2 - + 7 from dual;
I am expecting an error in later case too. Can we do any changes to the query to throw the error?
Thanks!

Answer 1

Hi,
If str is a string, then this expression
REGEXP_LIKE ( str
         , '(\d\s+\d)'     || -- digits, separated by 1 or more whitespace characters
           '|'          || -- or
           '([+*/-]\s*[+*/-]'   -- operators, separated by 0 or more whitespace characters
         )will return TRUE if (and only if) str contains either two consecutive digits (separated by at least 1 space character) or str contains two consectuive arithmetic operators (not necessaily separated by space characters).
You can include other operator symbols, by including them in both of the lists enclosed in square brackets. The hyphen ('-') must be the very first character or the very last character in the list; aside from that, the order of the symbols makes no difference.
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only) for all tables involved, and also post the results you want from that data.
Explain, using specific examples, how you get those results from that data.
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