我们可以编写多个select语句来从不同的表中提取数据 [英] Can we write multiple select statements to pull data from different tables

问题描述

我有多个表，没有一个是彼此相关的。



我想从数据库中选择数据并显示在表单加载第一个

时的表单。使用ms访问作为后端



有不同的参数，文本，列表框，工具提示，语言选择，在表单加载时从数据库中填充。

我正在使用后台线程，因此没有GUI问题。



但是将select语句写入一个函数是否正确下面。

I have multiple tables none of them is related to each other.

I want to select data from database and display it on the form when form loads for the first
time. using ms access as backend

There are different parameters, text , listboxes ,tooltips, Language selection, which are filled from database when form loads.
I am using background thread for this so no GUI issues.

But Is it right to write the select statement in one function as below.

void LoadDatafromDatabase()
{

try{

 OleDbConnection AccessConnection = new OleDbConnection(@"Provider = Microsoft.JET.OLEDB.4.0;data source =" + Application.StartupPath + "\\" + "FileDatabase.mdb;Jet OLEDB:Database password =;);

               AccessConnection.Open();

 //select query 1
    OledbCommand AccessCommand = new OleDbCommand("select Value from Parameters ",AccessConnection);
               DataReader = AccessCommand.ExecuteReader();
               
               int j=0;
               while (DataReader.Read())
               {
                   FormValue = DataReader.GetValue(1).ToString();
                   LoadFormValues[j] = FormValue;
                   j++;
               }        
//select query 2
 OledbCommand AccessCommand = new OleDbCommand("select Value from Tooltip",AccessConnection);
               DataReader = AccessCommand.ExecuteReader();
               
               int j=0;
               while (DataReader.Read())
               {
                   FormValue = DataReader.GetValue(1).ToString();
                   FormTooltip[j] = FormValue;
                   j++;
               }        

////select query 3...n
         .........      like this I have used different select queries for different 
   tables.

}

catch (Exception ex)
            {
               //catch exp
            }
            finally
            {
           //dispose open connenction ,datareader
            }
}

是吗一个好的编码实践

Is it a good coding practice

推荐答案

虽然可以从1个查询中获取多个数据表到数据集中，但是我测试它的唯一一次是非常慢，它是几年前我从未重复过这个实验。



我试图引入一些非常小的表来支持应用程序中的查找功能。

While it is possible to get back multiple datatables from 1 query into a dataset, the only time I tested this it was dismally slow, it was some years ago and I have never repeated the experiment.

I was attempting to pull in a number (6) of very small tables to support the lookup function in an application.

你的方法应如下所示



步骤1：将所有sql查询合并为一个。例如

Your approach should look like following

Step 1: merge all sql queries as one. For example

sql query = "select Value from Parameters;select Value from Tooltip;";

步骤2：执行查询并读取多个结果集

Step 2: Execute the query and read multiple resultset

using (OledbCommand command = new OledbCommand
       ("select Value from Parameters;select Value from Tooltip;", AccessConnection ))
{
    using (DataReader reader = command.ExecuteReader())
    {
        while (reader.Read())
        {
            MessageBox.Show(reader.GetString(0), "Table1.Column1");
        }

        if(reader.NextResult())
        {
           while (reader.Read())
          {
            MessageBox.Show(reader.GetString(0), "Table2.Column2");
          }
        }
    }
}

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