C# 选择不';返回结果
我对这个选择有问题。当我在MS Access上执行它时,结果会正确、完整地返回。当我试图通过C#执行它时,相同的查询不会返回任何结果。SELECT的前一个变体是由适配器实现的,用于在dataGridView中显示SELECT的结果。但是当我执行它时,我只得到一个带有列名的空表C# 选择不';返回结果,c#,ms-access,C#,Ms Access,我对这个选择有问题。当我在MS Access上执行它时,结果会正确、完整地返回。当我试图通过C#执行它时,相同的查询不会返回任何结果。SELECT的前一个变体是由适配器实现的,用于在dataGridView中显示SELECT的结果。但是当我执行它时,我只得到一个带有列名的空表 private void getByObjectAndPollutant(string Object, string Pollutant, int firstYear, int lastYear) {
private void getByObjectAndPollutant(string Object, string Pollutant,
int firstYear, int lastYear)
{
List<string> result = new List<string>();
// line breaks added without concatenation, for readability.
cmd = new OleDbCommand("SELECT object_name, p_name, mpc, emission_concentration,
[year] FROM Pollutants INNER JOIN (Objects INNER JOIN Emissions
ON Objects.o_id = Emissions.e_o_id) ON Pollutants.p_id = Emissions.e_p_id
WHERE (object_name = '" + Object + "' AND p_name = '" + Pollutant + "' AND
[year] BETWEEN " + firstYear + " AND " + lastYear + ") ;", con);
con.Open();
reader = cmd.ExecuteReader();
while (reader.Read()) {
var myString = reader.GetString(0);
result.Add(myString);
richTextBox1.Text += myString;
}
con.Close();
}
这是MS Access中的选择查询:
SELECT object_name, p_name, mpc, emission_concentration, year
FROM Pollutants
INNER JOIN (Objects
INNER JOIN Emissions ON Objects.o_id=Emissions.e_o_id)
ON Pollutants.p_id=Emissions.e_p_id
WHERE object_name="some name" And p_name="some name" And year Between 2011 And 2015;
这是之前的方法代码:
private void getByObjectAndPollutant(string Object, string Pollutant, int firstYear,
int lastYear)
{
con.Open();
DataTable dt = new DataTable();
adapt = new OleDbDataAdapter(this long select);
adapt.Fill(dt);
dataGridView2.DataSource = dt;
con.Close();
}
我使用reader或adapter的主要原因是为了获得SELECT查询的结果。这是你的选择吗?当这项工作完成后,我将根据选择编码绘制图表的方法。可能是组合/下拉列表。奇怪的是,
comboBox5.Text
返回选定的值,而不是文本
试着换成
string localObject = comboBox5.SelectedItem.Text;
string localPollutant = comboBox4.SelectedItem.Text;
你好!!最后我找到了解决办法。SELECT的主要目的是从数据库中获取一些数据,但在获取数据时,我并没有使用
Item,我使用一个Item的名称,它不返回任何结果。所以我想让我
尝试使用ID创建条件
因此,工作函数的代码:
工作函数调用的代码:
结果DataGridView我得到了正确的数据,我非常高兴!!!感谢所有试图帮助我的人
您可以共享在Access上执行的查询吗?我注意到的一个问题是您只使用dataReader.GetString(0)。其余的列根本不被访问。我还强烈建议使用字符串索引器datareader[“colName”]]可能是string.Join(reader.GetValues(),“”),作为快速检查,而不是getstring(0)。在添加行之后,您可能还需要新行。不幸的是,此答案可能重复,但不会更改任何内容。但这比仅仅从组合框中获取文本要好得多。我之前测试的是,我的组合框文本返回正确的值,并且它们返回正确的值。
string localObject = comboBox5.SelectedItem.Text;
string localPollutant = comboBox4.SelectedItem.Text;
private void getByObjectAndPollutant(int Object, int Pollutant, int firstYear, int lastYear)
{
con.Open();
DataTable dt = new DataTable();
adapt = new OleDbDataAdapter("SELECT mpc, emission_concentration FROM Pollutants INNER JOIN (Objects INNER JOIN Emissions ON Objects.o_id = Emissions.e_o_id) ON Pollutants.p_id = Emissions.e_p_id WHERE Objects.o_id=" + Object + " AND Pollutants.p_id=" + Pollutant + " AND Emissions.[year] BETWEEN " + firstYear + " AND " + lastYear + ";", con);
adapt.Fill(dt);
dataGridView2.DataSource = dt;
con.Close();
}
private void button5_Click(object sender, EventArgs e)
{
int localObject = Convert.ToInt32(comboBox4.SelectedValue.ToString());
int localPollutant = Convert.ToInt32(comboBox5.SelectedValue.ToString());
int localFirstYear = Convert.ToInt32(comboBox6.SelectedItem.ToString());
int localLastYear = Convert.ToInt32(comboBox7.SelectedItem.ToString());
getByObjectAndPollutant(localObject,localPollutant,localFirstYear,localLastYear);
}