我有一个关于这个SELECT语句的问题。当我在MS Access上执行它时,结果返回正确且完整。但是当我尝试通过C#执行它时,相同的查询没有返回任何结果。之前的SELECT语句是通过适配器实现的,以在dataGridView中显示选择结果。但是当我执行它时,我只得到一个带有列名的空表格。
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();
}
这是我在程序中的称呼:
private void button5_Click(object sender, EventArgs e) {
string localObject = comboBox5.Text.ToString();
string localPollutant = comboBox4.Text.ToString();
int localFirstYear = Convert.ToInt32(comboBox6.Text);
int localLastYear = Convert.ToInt32(comboBox7.Text);
getByObjectAndPollutant(localObject,localPollutant,localFirstYear,localLastYear);
}
这是 MS Access 中的 SELECT 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;
这是先前的方法代码:
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的主要原因是为了得到SELECT查询的结果。这个SELECT是否返回了一些内容?当这个工作成功后,我将编写基于SELECT绘制图表的方法。
List<string result = new List<string();
上缺少闭合的角括号。 - wazz