var steps = _db.tblConversions.GroupBy(c => c.CvStep).OrderBy(c=>c.Key).Select(s => s.Key).ToList();
foreach (var step in steps)
{
    var keywords =
      _db.ExecuteQuery<string>(
        "SELECT DISTINCT SkwKeyword FROM tblSearchKeywords WHERE  SkwIpAddress in (" +
        " SELECT DISTINCT CvIP FROM tblConversions " +
        " WHERE SkwIpAddress     IN (SELECT DISTINCT CvIP FROM tblConversions WHERE CvStep = {0}) " +
        "  AND  SkwIpAddress NOT IN (SELECT DISTINCT CvIP FROM tblConversions WHERE CvStep > {0}))",
        step);

    sb.AppendFormat("<tr><td>Stap&nbsp;{0}</td><td style=\"text-align:left;\">{1}</td></tr>",
            step,
            String.Join(" | ",keywords));
}