[Info-ingres] Using a literal '-' in a character class

[Roy Hann]

I am looking at some existing code that wants find rows where an
attribute contains one of a set of special character, including
an ASCII dash.

The original code was similar to this:

  WHERE col LIKE '%\[.,;:\-&@\]%' ESCAPE '\'

which provoked the error message:

  E_AD1018 Illegal pattern match specified:  Illegal ESCAPE sequence.
    The ESCAPE char must be followed by one of:
        `%' (percent)
        `_' (underscore)
        `[' (left square bracket)
        `]' (right square bracket)
    another ESCAPE char.

Moving the dash to the start of the character class and not escaping it
works as intended, thus:

  WHERE col LIKE '%\[-.,;:&@\]%' ESCAPE '\'

So, my questions are: (1) did I get lucky and find a bug that works in
my favour. If not, (2) is this standard behaviour (i.e. ANSI/ISO
standard) that I can expect to work always everywhere?

Roy

PS: For the record, moving the '-' to the end does _not_ work. It
provokes a different error:

  E_AD1015 Illegal pattern match specified.  One of the following:
    o  An opening `[' without a closing `]'
        o  Vice-versa
        o  Range ending with `-]'
        o  Range of the form `[x-y]' where char `y' comes before `x'.