Access数据库 ：要查找处于两个字符串之间的值，如何写

Access数据库 ：要查找处于两个字符串之间的值，怎么写？
private void selectActivity(int index, string s1,string s2)
{

  string sql= "select * from acttable where where act_start>='" + s1 + "' and act_stop<='" + s2 + "'"; 

}
我要在数据库中查找大于s1 且小于s2之间的所有记录，但照上面sql语句执行 ，不对！求大神！！！！

[解决办法]
去掉单引号。
[解决办法]
是什么类型？如果日期的话试试看between
[解决办法]
string sql= "select * from acttable where where act_start>='" + s1 + "' and act_stop<='" + s2 + "'";

里面多了个where

string sql= "select * from acttable where act_start>='" + s1 + "' and act_stop<='" + s2 + "'";
另外还可以试试

string sql= "select * from acttable where act_start between #" + s1 + "# and #" + s2 + "#";

[解决办法]

SQL code

DECLARE @t table(    id int,    cDate datetime)insert into @t  select 1, GETDATE()  union  select 2, DATEADD("D",1,GETDATE())  union  select 3, DATEADD("D",2,GETDATE())  DECLARE @start datetime='2012-10-04'DECLARE @end datetime='2012-10-07'SELECT *FROM @tWHERE cDate between @start and @end--测试结果--1    2012-10-04 15:40:33.360--2    2012-10-05 15:40:33.360--3    2012-10-06 15:40:33.360