两个日期之间的总收入不工作c＃ms访问数据库

Question

我正在创建一个MS Access作为数据库后端的C＃项目。我想显示两个日期之间的价格总和。我已创建以下查询方法：

public DataTable selectDates(string dateFrom,string dateTo) 
{ 
    initilize(); 
    _conn.ConnectionString = _cs; 
    _cmd.Connection = _conn; 

    _cmd.CommandText = "Select Sum(tPrice) AS Price from [tblInventory] where Date_Of_Installation BETWEEN '" + dateFrom + "' AND '" + dateTo + "'"; 
    _da.SelectCommand = _cmd; 
    _da.Fill(_dt); 
    return _dt; 
} 

在窗体端我有两个时间选择器和一个按钮：

private void btnTotalRevenue_Click(object sender, EventArgs e) 
{ 
    dt = db.selectDates((pickerDateFrom.Text).ToString().Trim(), (pickerDateTo).ToString().Trim()); 
    string a = dt.Rows[0]["Price"].ToString(); 
    MessageBox.Show(a); 
} 

但在MessageBox是显示一个空字符串：。

Answer 1

在MS Access中，您需要格式化日期并将其包裹在＃符号中。

示例。

SELECT Sum(tPrice) AS Price from [tblInventory] 
WHERE Date_Of_Installation BETWEEN #2016/01/01# AND #2016/02/01# 

所以你的C＃应该成为。

private void btnTotalRevenue_Click(object sender, EventArgs e) 
{ 
    dt = db.selectDates(pickerDateFrom.SelectedDate.Value.ToString("#yyyy/MM/dd#"), pickerDateTo.SelectedDate.Value.ToString("#yyyy/MM/dd#")); 
    string a = dt.Rows[0]["Price"].ToString(); 
    MessageBox.Show(a); 
} 

Answer 2

尝试查询更改为：

_cmd.CommandText = "Select Sum(tPrice) AS Price from [tblInventory] where 
Date_Of_Installation BETWEEN '" + dateFrom.ToString("yyyy-MM-dd") + "' AND '" + 
dateTo.ToString("yyyy-MM-dd") + "'"; 

Answer 3

您可以使用日期时间参数梅索德selectDates这样的：

public DataTable selectDates(DateTime dateFrom, DateTime dateTo) 
{ 
    initilize(); 
    _conn.ConnectionString = _cs; 
    _cmd.Connection = _conn; 
    string query = string.Format("Select Sum(tPrice) AS Price from [tblInventory] where Date_Of_Installation BETWEEN #{0}# AND #{1}#", dateFrom.ToString("yyyy/MM/dd"), dateTo.ToString("yyyy/MM/dd")); 
    _cmd.CommandText = query; 
    _da.SelectCommand = _cmd; 
    _da.Fill(_dt); 
    return _dt; 
} 

和呼叫方法的DateTimePicker的wiyhout套价值串状这个：

void btnTotalRevenue_Click(object sender, EventArgs e) 
{ 
    dt = db.selectDates(pickerDateFrom.Value, pickerDateTo.Value); 
    string a = dt.Rows[0]["Price"].ToString(); 
    MessageBox.Show(a); 
} 

不过，我建议你使用参数使用DbType.DateTime，然后直接传递日期时间的参数（无需转换），还可以避免SQL注入，像这样：

public DataTable selectDates(DateTime dateFrom, DateTime dateTo) 
{ 
    initilize(); 
    _conn.ConnectionString = _cs; 
    string query = "Select Sum(tPrice) AS Price from [tblInventory] where Date_Of_Installation BETWEEN @startDate AND @endDate"; 
    OleDbCommand _cmd = new OleDbCommand(query, _conn); 
    cmd.Parameters.AddWithValue("@startDate ", DbType.DateTime).Value = dateFrom; 
    cmd.Parameters.AddWithValue("@endDate ", DbType.DateTime).Value = dateTo; 
    _da.SelectCommand = _cmd; 
    _da.Fill(_dt); 
    return _dt; 
}