我写有一张进货表,然后我打算统计一共进了多少种货物,就写了以下语句:
this.myCommand.CommandText = "select distinct count(*) number from Buy";
SqlDataReader myDataReader = this.myCommand.ExecuteReader();
String num = myDataReader["number"].ToString();
MessageBox.Show("共有货物品种" + num + "种");
myDataReader.Close();
我原本打算用SQL语句:select distinct count(*) number from Buy 来做统计,然后以String num = myDataReader["number"].ToString()来取得统计数据,但是发现行不通。那么如果以select distinct count(*) number from Buy 来做统计后,如何取得结果?
this.myCommand.CommandText = "select distinct count(*) number from Buy";
SqlDataReader myDataReader = this.myCommand.ExecuteReader();
String num = myDataReader["number"].ToString();
MessageBox.Show("共有货物品种" + num + "种");
myDataReader.Close();
我原本打算用SQL语句:select distinct count(*) number from Buy 来做统计,然后以String num = myDataReader["number"].ToString()来取得统计数据,但是发现行不通。那么如果以select distinct count(*) number from Buy 来做统计后,如何取得结果?
我看书上写的是:select distinct count(*) number from Buy
书是人民邮电出版社出的SQL语言与数据库管理。
distinct count(*)是无意义的,因为count出来本来就只有一个数值,应该用count(distinct *)吧
i = 0