操作数据库日期字段

（1）向SQL Server数据库中的日期字段插入值：

           string strconn = @"server=.\student;database=test;uid=sa;pwd=123456";
            DateTime t;
            if(!DateTime.TryParse(textBox3.Text,out t))   //检查日期格式是否正确
            {
                MessageBox.Show("日期出入有误，请修改");
                return;
            }
            using (SqlConnection conn = new SqlConnection(strconn))
            {
                string sql = string.Format("insert into student_info(stud_id,stud_name,enter_date) values('{0}','{1}','{2}')", textBox1.Text, textBox2.Text, t);
                SqlCommand cmd = new SqlCommand(sql, conn);
                conn.Open();
                cmd.ExecuteNonQuery();
            }

      由此可知，SQL Server是把日期字段当作字符串类型来处理的。所以只要日期格式正确的话，不用转换，直接用文本框中的值插入数据库中也是可行的。即sql语句可以为：

            string sql = string.Format("insert into student_info(stud_id,stud_name,enter_date) values('{0}','{1}','{2}')", textBox1.Text, textBox2.Text, textBox3.Text);
             当然这种利用字符串拼接产生sql语句的方法并不推荐！

            如果用DateTimePicker控件，sql语句可以为：

            string sql = string.Format("insert into student_info(stud_id,stud_name,enter_date) values('{0}','{1}','{2}')", textBox1.Text, textBox2.Text, dateTimePicker1.Value);

查询某个时间段内的记录可以用如下的代码：

            using (SqlConnection conn = new SqlConnection(strconn))
            {
                string sql = string.Format("select * from student_info where enter_date between '{0}' and '{1}'", dateTimePicker2.Value, dateTimePicker3.Value);
                SqlCommand cmd = new SqlCommand(sql, conn);
                conn.Open();
                using (SqlDataReader rd = cmd.ExecuteReader())
                {
                    DataTable dt = new DataTable();
                    dt.Load(rd);
                    dataGridView1.DataSource = dt;
                }
            }
（2）操作Access日期字段：

      插入数据的sql语句：               

      string sql = string.Format("insert into test(name,enterdate) values('{0}',#{1}#)", textBox2.Text, textBox3.Text);

      查询某个时间段内的记录可以用如下的sql语句：
     string sql = string.Format("select * from test where enterdate between #{0}# and #{1}#", dateTimePicker1.Value.ToShortDateString(), dateTimePicker3.Value.ToShortDateString());