c＃mysqlsum查询到标签-c#mysqlsumquerytolabel

0  

I would do some modifications to your code because for one thing your are not properly disposing of your objects, also you stated that you have it in the button click method which I would get that out of there and make this its own function.

我会对你的代码进行一些修改,因为有一件事你没有正确处理你的对象,你也说你在按钮点击方法中有它,我会从那里得到它并使它成为它自己的功能。

private string performSQL() 
{
   string result = "select sum(purprice) from localcollection";
   using (SqlCeConnection mycOnn= new SqlCeConnection("ConnectionString"))
   using (SqlCeCommand showresult = new SqlCeCommand(result, myconn))
   {
      try
      {
          myconn.Open();
          return showresult.ExecuteScalar().ToString();

      }catch(System.Exception ex)
      {
          MessageBox.Show(ex.ToString());
          // or log exception how ever you prefer
      }finally
      {
          //the finally ensures your connection gets closed
          myconn.Close();
      }
   }
   return "";
}

1  

If you are only looking to return one value from a query, then ExecuteScalar is what you should be using, . The ExecuteReader is better for forward-only reads of multiple records, so it's overkill for your situation

如果您只想从查询中返回一个值,那么ExecuteScalar就是您应该使用的,。 ExecuteReader更适用于多个记录的仅向前读取,因此对您的情况来说太过分了

Take a look here for a comparisson What is the difference between ExecuteScalar, ExecuteReader and ExecuteNonQuery?

看一看comparisson ExecuteScalar,ExecuteReader和ExecuteNonQuery有什么区别?

0  

Best practice, use ExecuteScalar when you are returning 1 row and 1 column of data (which your query does.) As a result, go with ExecuteScalar.

最佳实践,当您返回1行和1列数据(您的查询所执行的数据)时,请使用ExecuteScalar。因此,请使用ExecuteScalar。

0  

Make sure the name of the column you are trying to add is purprice, and that it is a numeric type. Also make sure it doesn't contain NULL values.

确保您尝试添加的列的名称是purprice,并且它是数字类型。还要确保它不包含NULL值。

0  

I think your code is ok, but you missed :

我认为你的代码还可以,但你错过了:

  SqlCeCommand cmd = new SqlCeCommand("select sum(purprice) from localcollection",myconn);

that's all, hope it works

这就是全部,希望它有效

0  

Just add AS after SUM() like the row below:

只需在SUM()之后添加AS,如下面的行:

select sum(purprice) AS purprice from localcollection

select local(purprice)来自localcollection的AS purprice

And you are good to go.

你很高兴。