如何获取另一列项目值=值的列的总和？

Question

我的代码：

string hweight = "Hunters";
string hsql = "SELECT SUM(Weight), Product From Opened WHERE Product =" + hweight;

OleDbCommand hcmd = new OleDbCommand(hsql,conn);
txtHunters.Text = hcmd.ExecuteScalar().ToString();

然后我收到以下错误：

  

您尝试执行的查询不包含指定的表达式＆＃39;产品＆＃39;作为集合函数的一部分。

Answer 1

您尝试选择一个字段/列并同时使用聚合函数，这仅在您为所选字段/列提供group by子句时才有效：

string hsql = "SELECT SUM(Weight), Product FROM Opened WHERE Product ='" + hweight + "' GROUP BY Product";

Answer 2

你的SQL应该是：

SELECT SUM(Weight), Product From Opened WHERE Product =" + hweight + " GROUP BY Product"

当您使用聚合函数时，您应该按某种方式对它们进行分组！在你的情况下，产品领域！

Answer 3

试试这个，

string hweight = "Hunters";
string hsql = "SELECT SUM(Weight), Product From Opened WHERE Product =" + hweight + " GROUP BY Product";
OleDbCommand hcmd = new OleDbCommand(hsql,conn);
txtHunters.Text = hcmd.ExecuteScalar().ToString();