正则表达式的匹配问题

[aloneone]

代码是帮助的示例，仅改动了text与pat的值。

        private void button4_Click(object sender, EventArgs e)
        {
            string text = "select * from blue order by a";
            string pat = @"(select)|(from)|(order)|(by)";
            // Compile the regular expression.
            Regex r = new Regex(pat, RegexOptions.IgnoreCase);
            // Match the regular expression pattern against a text string.
            Match m = r.Match(text);
            int matchCount = 0;
            while (m.Success)
            {
                Console.WriteLine("Match" + (++matchCount));
                for (int i = 1; i <= 2; i++)
                {
                    Group g = m.Groups[i];
                    Console.WriteLine("Group" + i + "='" + g + "'");
                    CaptureCollection cc = g.Captures;
                    for (int j = 0; j < cc.Count; j++)
                    {
                        Capture c = cc[j];
                        System.Console.WriteLine("Capture" + j + "='" + c + "', Position=" + c.Index);
                    }
                }
                m = m.NextMatch();
            }
        }

====我想捕获select/from/order/by这四个关键字，输出结果如下：
Match1
Group1='select'
Capture0='select', Position=0
Group2=''
Match2
Group1=''
Group2='from'
Capture0='from', Position=9
Match3
Group1=''
Group2=''
Match4
Group1=''
Group2=''
====我的问题有两个（1个问题20分）
1.为什么会有Group1或Group2为空字符（''）的捕获结果？
2.为什么order与by未被捕获到？

[游戏人间]

for (int i = 1; i <= 2; i++) 为什么是<=2呢? 那不是只能显示2组吗? 加 上order by 不是有4组.

[q107770540]

这代码写的够乱的，挺简单一事让你搞复杂了：

		 string text = "select * from blue order by a";
			string pat = @"(?:select)|(?:from)|(?:order)|(?:by)";
			// Compile the regular expression.
			Regex r = new Regex(pat, RegexOptions.IgnoreCase);
			
			foreach(Match m in r.Matches(text))		
			{
			  foreach(Capture c in m.Captures)
			  	Console.WriteLine(c.Value);
			}