接上篇
select为从数据表中检索数据,用法如下:代码写在按钮“readdata”下面。“list”为控件ListBox的名称,本案例是将检索结果放在控件ListBox中显示。常用检索方式有以下几种
private void readdata_Click(object sender, RoutedEventArgs e)
{
string connStr = ConfigurationManager.ConnectionStrings["connStr"].ConnectionString;
using (MySqlConnection connect = new MySqlConnection(connStr))
{
string sql = "select * from students";
MySqlCommand cmd = new MySqlCommand(sql, connect);
connect.Open();
MySqlDataReader mdr = cmd.ExecuteReader();
while (mdr.Read())
{
list.Items.Add("id "+mdr[0].ToString() +"name "+ mdr[1].ToString() +"class "+ mdr[2].ToString() +"score "+ mdr[3].ToString());
}
connect.Close();
}
}
方式1:每行所有列
string sql = "select * from students";
方式2:每行的“id”“name”两列
string sql = "select id, from students";
方式3:使用”limit“可以限制检索结果的数量,本例只输出检索结果前两条
string sql = "select * from students limit 2";
方式4:使用"offset”表示从第二条开始,输出两条检索结果
string sql = "select * from students limit 2 offset 1";
方式5:检索成绩等于123的结果。
string sql = "select * from students where score = 123";
方式6:检索“score”大于13的结果。其它还有 >=,<=,!= 等符号。
string sql = "select * from students where score>13";
方式7:使用“or”检索,满足一个条件即可。
string sql = "select * from students where class=13 or score=13";
方式8:使用“order by”对检索数据进行排序,默认升序(asc)。在"score“后面添加“desc”,表示降序排序。
string sql = "select * from students order by score";