string text = "select * from [admin] where aa=1 and cc='b' order by aa desc ";
Regex reg = null;
reg = new Regex(@"\s+from\s+.*?(\s+where\s+|\s+order\s+|\s+group\s+)|\s+from\s+.+", RegexOptions.IgnoreCase);
string table = reg.Match(text).Value;
table = Regex.Replace(table.ToLower(), @"\s+from\s+|\s+where\s+|\[|\]|\s+order\s+|\s+group\s+", "");
reg = new Regex(@"select\s+.*?\s+from\s+", RegexOptions.IgnoreCase);
string field = reg.Match(text).Value;
field = Regex.Replace(field.ToLower(), @"select\s+|\s+from\s+|\[|\]", "");
reg = new Regex(@"\s+where\s+.*?(\s+order\s+|\s+group\s+)|\s+where\s+.+", RegexOptions.IgnoreCase);
string condition = reg.Match(text).Value;
condition = Regex.Replace(condition.ToLower(), @"\s+where\s+|\s+order\s+|\s+group\s+|\[|\]", "");
reg = new Regex(@"\s+order\s+by\s+.*?\s(desc|asc)|\s+order\s+by\s+.*?\s", RegexOptions.IgnoreCase);
string order = reg.Match(text).Value;
order = Regex.Replace(order.ToLower(),@"\s+order\s+by\s+|\[|\]", "");