Regex to remove single-line SQL comments (--)

Question

Question:

Can anybody give me a working regex expression (C#/VB.NET) that can remove single line comments from a SQL statement ?

I mean these comments:

Answer 1

As a late solution, the simplest way is to do it using ScriptDom-TSqlParser:

// https://michaeljswart.com/2014/04/removing-comments-from-sql/
// http://web.archive.org/web/*/https://michaeljswart.com/2014/04/removing-comments-from-sql/
public static string StripCommentsFromSQL(string SQL)
{
    Microsoft.SqlServer.TransactSql.ScriptDom.TSql150Parser parser = 
        new Microsoft.SqlServer.TransactSql.ScriptDom.TSql150Parser(true);

    System.Collections.Generic.IList errors;


    Microsoft.SqlServer.TransactSql.ScriptDom.TSqlFragment fragments = 
        parser.Parse(new System.IO.StringReader(SQL), out errors);

    // clear comments
    string result = string.Join(
      string.Empty,
      fragments.ScriptTokenStream
          .Where(x => x.TokenType != Microsoft.SqlServer.TransactSql.ScriptDom.TSqlTokenType.MultilineComment)
          .Where(x => x.TokenType != Microsoft.SqlServer.TransactSql.ScriptDom.TSqlTokenType.SingleLineComment)
          .Select(x => x.Text));

    return result;

}

or instead of using the Microsoft-Parser, you can use ANTL4 TSqlLexer

or without any parser at all:

private static System.Text.RegularExpressions.Regex everythingExceptNewLines = 
    new System.Text.RegularExpressions.Regex("[^\r\n]");


// http://drizin.io/Removing-comments-from-SQL-scripts/
// http://web.archive.org/web/*/http://drizin.io/Removing-comments-from-SQL-scripts/
public static string RemoveComments(string input, bool preservePositions, bool removeLiterals = false)
{
    //based on http://stackoverflow.com/questions/3524317/regex-to-strip-line-comments-from-c-sharp/3524689#3524689
    var lineComments = @"--(.*?)\r?\n";
    var lineCommentsOnLastLine = @"--(.*?)$"; // because it's possible that there's no \r\n after the last line comment
                                              // literals ('literals'), bracketedIdentifiers ([object]) and quotedIdentifiers ("object"), they follow the same structure:
                                              // there's the start character, any consecutive pairs of closing characters are considered part of the literal/identifier, and then comes the closing character
    var literals = @"('(('')|[^'])*')"; // 'John', 'O''malley''s', etc
    var bracketedIdentifiers = @"\[((\]\])|[^\]])* \]"; // [object], [ % object]] ], etc
    var quotedIdentifiers = @"(\""((\""\"")|[^""])*\"")"; // "object", "object[]", etc - when QUOTED_IDENTIFIER is set to ON, they are identifiers, else they are literals
                                                          //var blockComments = @"/\*(.*?)\*/";  //the original code was for C#, but Microsoft SQL allows a nested block comments // //https://msdn.microsoft.com/en-us/library/ms178623.aspx

    //so we should use balancing groups // http://weblogs.asp.net/whaggard/377025
    var nestedBlockComments = @"/\*
                         (?>
                         /\*  (?)      # On opening push level
                         | 
                         \*/ (?<-LEVEL>)     # On closing pop level
                         |
                         (?! /\* | \*/ ) . # Match any char unless the opening and closing strings   
                         )+                         # /* or */ in the lookahead string
                         (?(LEVEL)(?!))             # If level exists then fail
                         \*/";

    string noComments = System.Text.RegularExpressions.Regex.Replace(input,
        nestedBlockComments + "|" + lineComments + "|" + lineCommentsOnLastLine + "|" + literals + "|" + bracketedIdentifiers + "|" + quotedIdentifiers,
        me => {
            if (me.Value.StartsWith("/*") && preservePositions)
                return everythingExceptNewLines.Replace(me.Value, " "); // preserve positions and keep line-breaks // return new string(' ', me.Value.Length);
     else if (me.Value.StartsWith("/*") && !preservePositions)
                return "";
            else if (me.Value.StartsWith("--") && preservePositions)
                return everythingExceptNewLines.Replace(me.Value, " "); // preserve positions and keep line-breaks
     else if (me.Value.StartsWith("--") && !preservePositions)
                return everythingExceptNewLines.Replace(me.Value, ""); // preserve only line-breaks // Environment.NewLine;
     else if (me.Value.StartsWith("[") || me.Value.StartsWith("\""))
                return me.Value; // do not remove object identifiers ever
     else if (!removeLiterals) // Keep the literal strings
         return me.Value;
            else if (removeLiterals && preservePositions) // remove literals, but preserving positions and line-breaks
     {
                var literalWithLineBreaks = everythingExceptNewLines.Replace(me.Value, " ");
                return "'" + literalWithLineBreaks.Substring(1, literalWithLineBreaks.Length - 2) + "'";
            }
            else if (removeLiterals && !preservePositions) // wrap completely all literals
         return "''";
            else
                throw new System.NotImplementedException();
        },
        System.Text.RegularExpressions.RegexOptions.Singleline | System.Text.RegularExpressions.RegexOptions.IgnorePatternWhitespace);
    return noComments;
}