Question

I am not an expert but I am trying to write .NET regex expression to exclude SQL comment lines. Unfortunately I cannot find a proper description of how to use exclusion groups to find regex matches on another regex match: (‘.*?’) .

This regex finds all text between quotes but it also includes SQL comment areas (/*..*/ and –..):

'.*?'

Everything I tried it does not work as I am expecting.

My test sample:

    IF @RetValue = 'Cat'
   /*SET @RetValue = 'WrongLocation
and it works here' */
   ------testing line
SET @Dude = 'Punto'
/* comments */
    -- But it doesn't work here because inside comments! 
    -- and this is aren't the end
    SET @RetValue = 'But this should
work here'

Correct match should return only this:

'Cat'
''Punto'
and
'But this should
work here'

Answer 1

I can’t find an elegant RegEx to do what you want in one step, but you can do it in two steps.

string commentFree = Regex.Replace(sourceString, @"\/\*.*?\*\/|\-\-[^\n]*\n", string.Empty, RegexOptions.Multiline | RegexOptions.Singleline);

Now you can run the RegEx '[^']*' on commentFree to extract your fields.

Note that '[^']*' is more efficient than '.*?', because it removes the need for the RegEx engine to backtrack. Now it’ll find the start quote, continue for all characters that themselves aren’t a quote, and finish with the end quote. The same technique is used above to grab the comment after -- until the end of the line \n.

Edit: Alternately, you can use the pattern \/\*.*?\*\/|\-\-[^\n]*\n|'[^']*' to match all comments and quote blocks (that are not within comments), and then only use the matches that begin with ' when iterating through the results, as those will be the quote blocks.