如何解决参数@Something 没有默认值Access 数据库、Visual Studio VB.NET
我正在使用 Access 数据库来存储错误发生的记录,以跟踪其数量和频率。多亏了本网站上一些天才程序员的大力帮助,我现在离我的最终目标越来越近了,即将发生计数从数据库中提取出来,并在 Visual Studio 程序中提取到图表中。
我遇到的问题是在我的函数中的这一行抛出了一个错误:
count = command.ExecuteScalar()
错误如下:
System.Data.OleDb.OleDbException: '参数@MY_OF_LOG 没有默认值。'
我成功地为计数返回了一个值,即 0。这是一个可能的值,但我现在想知道计数返回为零的事实是否可能是导致此错误的部分原因?
注意:每个月从这些计数中返回的值将用作图表的 y 值。
有没有人知道为什么会发生这个错误?我将在下面插入我的代码片段。感谢您的帮助。
Private Function CountMissedParts() Handles MyBase.Load
Dim sql = $"SELECT COUNT(*)
FROM DataCollection
WHERE [MISSED PART] = 'Missed Part'
AND [M/Y OF LOG] = @MY_OF_LOG;"
Dim JANmyOfLog = #1/1/2021#
Dim FEBmyOfLog = #2/1/2021#
Dim MARmyOfLog = #3/1/2021#
Dim APRmyOfLog = #4/1/2021#
Dim MAYmyOfLog = #5/1/2021#
Dim JUNmyOfLog = #6/1/2021#
Dim JULmyOfLog = #7/1/2021#
Dim AUGmyOfLog = #8/1/2021#
Dim SEPmyOfLog = #9/1/2021#
Dim OCTmyOfLog = #10/1/2021#
Dim NOVmyOfLog = #11/1/2021#
Dim DECmyOfLog = #12/1/2021#
Dim count As Integer
Dim JanuaryMP As Double
Dim FebruaryMP As Double
Dim MarchMP As Double
Dim AprilMP As Double
Dim MayMP As Double
Dim JuneMP As Double
Dim JulyMP As Double
Dim AugustMP As Double
Dim SeptemberMP As Double
Dim OctoberMP As Double
Dim NovemberMP As Double
Dim DecemberMP As Double
Using connection As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Database1.accdb"),command As New OleDbCommand(sql,connection)
JanuaryMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = JANmyOfLog
FebruaryMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = FEBmyOfLog
MarchMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = MARmyOfLog
AprilMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = APRmyOfLog
MayMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = MAYmyOfLog
JuneMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = JUNmyOfLog
JulyMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = JULmyOfLog
AugustMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = AUGmyOfLog
SeptemberMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = SEPmyOfLog
OctoberMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = OCTmyOfLog
NovemberMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = NOVmyOfLog
DecemberMP = command.Parameters.Add("@MY_OF_LOG",OleDbType.Date).Value = DECmyOfLog
connection.Open()
count = command.ExecuteScalar()
' set 0,0
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(0,0)
' other points
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(1,JanuaryMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(2,FebruaryMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(3,MarchMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(4,AprilMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(5,MayMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(6,JuneMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(7,JulyMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(8,AugustMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(9,SeptemberMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(10,OctoberMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(11,NovemberMP)
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(12,DecemberMP)
End Using
NotInEpicorCHRT.ChartAreas(0).AxisX.Minimum = 0.0
NotInEpicorCHRT.ChartAreas(0).AxisX.Maximum = 12
NotInEpicorCHRT.ChartAreas(0).AxisX.Interval = 1
NotInEpicorCHRT.ChartAreas(0).AxisY.Minimum = 0.0
NotInEpicorCHRT.ChartAreas(0).AxisY.Maximum = 45
NotInEpicorCHRT.ChartAreas(0).AxisY.Interval = 5
End Function
解决方法
一个小小的警告:我对图表没有太多经验,但其他东西应该没问题。
重要的部分是:
Dim logDates() As DateTime ...
这声明了一个 DateTime 数组。当您打算遍历值时,数组是一种存储相同类型的多个值的简单方法。我还冒昧地使用 VB.Net DateTime 类型来明确说明年、月和日期值。这种方法会让你和其他阅读你代码的人更清楚。
For counter As Integer = 0 To logDates.Count - 1
数据库命令执行 12 次,对数组中的每个条目执行一次。
Using Command As New OleDbCommand(sql,connection)
Command.Parameters.Add("MY_OF_LOG",OleDbType.Date).Value = logDates(counter)
Dim returnValue = Command.ExecuteScalar()
Dim count As Integer = Integer.Parse(returnValue.ToString)
' other points
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(counter + 1,count)
End Using
ExecuteScalar 的返回值然后使用您原来的索引放入图表系列
整个代码建议如下:
Public Sub CountMissedParts()
Dim logDates() As DateTime = {New DateTime(2021,1,1),New DateTime(2021,2,3,4,5,6,7,8,9,10,11,12,1)}
' set 0,0
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(0,0)
Using connection As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Database1.accdb")
connection.Open()
For counter As Integer = 0 To logDates.Count - 1
Dim sql = $"SELECT COUNT(*) FROM DataCollection WHERE [MISSED PART] = 'Missed Part' AND [M/Y OF LOG] = @MY_OF_LOG;"
Using Command As New OleDbCommand(sql,connection)
Command.Parameters.Add("MY_OF_LOG",OleDbType.Date).Value = logDates(counter)
Dim returnValue = Command.ExecuteScalar()
Dim count As Integer = Integer.Parse(returnValue.ToString)
' other points
NotInEpicorCHRT.Series("Missed Part").Points.AddXY(counter + 1,count)
End Using
Next
End Using
NotInEpicorCHRT.ChartAreas(0).AxisX.Minimum = 0.0
NotInEpicorCHRT.ChartAreas(0).AxisX.Maximum = 12
NotInEpicorCHRT.ChartAreas(0).AxisX.Interval = 1
NotInEpicorCHRT.ChartAreas(0).AxisY.Minimum = 0.0
NotInEpicorCHRT.ChartAreas(0).AxisY.Maximum = 45
NotInEpicorCHRT.ChartAreas(0).AxisY.Interval = 5
End Sub
,
既然你已经接受了答案,我认为你的问题已经解决了。我的函数看起来像这样。
#include <bits/stdc++.h>
#include <iostream>
#include <stdlib.h>
using namespace std;
int getProduct(int n)
{
int product = 1;
while (n != 0) {
product = product * (n % 10);
n = n / 10;
}
return product;
}
int main()
{
int n;
cout << "insert n ";
cin >> n;
if (n >= 1000 && n <= 9999 && n /! 2) {
cout << (getProduct(n));
}
}
用法。
Private Function CountMissedParts() As DataTable
Dim sql = "SELECT [M/Y OF LOG],COUNT([Missed Part]) As Total
FROM [Data Collection]
WHERE [MISSED PART] = 'MISSED PART' GROUP BY [M/Y OF LOG]
ORDER BY [M/Y OF LOG];"
Using dt As New DataTable
Using connection As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Database1.accdb"),command As New OleDbCommand(sql,connection)
connection.Open()
Using reader = command.ExecuteReader
dt.Load(reader)
End Using
End Using
Return dt
End Using
End Function
顺便说一句,如果上一个答案不起作用,您可以再次点击检查并选择另一个答案。
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