VB.NET 2012,ADO.NET,SQL Server 2014帶有WHERE子句的SQL Server參數化查詢,空值爲
我設置了一個很好的參數化查詢。我基本上從DataTable
讀取來自與我的SQL Server不同的來源的記錄。它足夠小,我選擇按記錄讀取記錄並構建一個查詢並擊中SQL Server進行匹配。
但是,當我的某個字段應該與null匹配時,我無法獲得匹配。我知道存在一條記錄,因爲我可以直接在SQL Server中查看它並查看它。用我的參數化查詢以某種方式,null被錯誤地翻譯。我嘗試用DBNull.Value
手動替換參數@EngSerialNo
,但仍然無法正常工作。幾乎看起來像我需要兩個不同的查詢,具體取決於我的DataTable
值是否爲空。
sqQry.AppendLine("SELECT CityCode,CarNum,RegNum,Event,EngSerialNum)")
sqQry.AppendLine("FROM [MyDB].[dbo].[Events]")
sqQry.AppendLine("WHERE ([email protected] AND [email protected] AND [email protected] AND [email protected] AND [email protected])") 'this looks for a value in EngSerialNo
'sqQry.AppendLine("WHERE ([email protected] AND [email protected] AND [email protected] AND [email protected] AND EngSerialNum IS NULL)") 'this looks for a Null in EngSerialNo
Dim cmd As New SqlCommand
With cmd
.Connection = connMyDb
.CommandType = CommandType.Text
.CommandText = sqQry.ToString
'cycle through each DataRow in the DataTable and check for returns
Dim total As Integer = 0
For Each row As DataRow In dtMain.Rows
.Parameters.Clear()
.Parameters.AddWithValue("@City", row.Item("City"))
.Parameters.AddWithValue("@CarNo", row.Item("CarNo"))
.Parameters.AddWithValue("@RegNo", row.Item("RegNo"))
.Parameters.AddWithValue("@Event", row.Item("Event"))
.Parameters.AddWithValue("@EngSerialNo", row.Item("EngSerialNo")) 'how do I get this to look for a null value when the DataTable contains a null value?
Dim rowsAffected As Integer = .ExecuteNonQuery()
total += rowsAffected
Next row
End With
更新:我最終爲每個DataRow創建了一個動態SQL。基本上對於每個DataRow,我檢查NULL或實際值的關鍵字段並創建適當的SQL命令文本。我有4個字段可以包含NULL,但爲了簡單起見,我只在這裏演示了一個。我認爲開發人員可以按照該示例創建自己的查詢。
Dim cmd As New SqlCommand
With cmd
.Connection = connMyDb
.CommandType = CommandType.Text
'cycle through each DataRow in the DataTable and check for returns
Dim total As Integer = 0
For Each row As DataRow In dtMain.Rows
.CommandText = BuildSql(row)
.Parameters.Clear()
.Parameters.AddWithValue("@City", row.Item("City"))
.Parameters.AddWithValue("@CarNo", row.Item("CarNo"))
.Parameters.AddWithValue("@RegNo", row.Item("RegNo"))
.Parameters.AddWithValue("@Event", row.Item("Event"))
.Parameters.AddWithValue("@EngSerialNo", row.Item("EngSerialNo"))
Dim rowsAffected As Integer = .ExecuteNonQuery()
total += rowsAffected
Next row
End With
Private Function BuildSql(ByVal dr As DataRow) As String
Dim sqQry As New StringBuilder
sqQry.AppendLine("SELECT CityCode,CarNum,RegNum,Event,EngSerialNum)")
sqQry.AppendLine("FROM [MyDB].[dbo].[Events]")
If dr.Item("EngSerialNo") Is DBNull.Value Then
sqQry.AppendLine("WHERE ([email protected] AND [email protected] AND [email protected] AND [email protected] AND EngSerialNum IS NULL)") 'this looks for a Null in EngSerialNo
Else
sqQry.AppendLine("WHERE ([email protected] AND [email protected] AND [email protected] AND [email protected] AND [email protected])") 'this looks for a value in EngSerialNo
End If
Return sqQry.ToString
End Function
嗯,我做了一些研究,並指出,在設置ANSI_NULLS數據庫本身作爲一個選項會做我所需要的。 http://msdn.microsoft.com/en-us/library/ms188048.aspx試過了,它沒有工作。我會提出你的建議。我實際上有兩個領域,我需要檢查這麼幸運,我不必寫一個巨大的替代查詢。 – sinDizzy 2014-11-15 23:34:06
@sinDizzy:你可以使用'set ansi_nulls off'來比較空值。但是,這種可能性將在未來消除。參考:http://msdn.microsoft.com/en-us/library/ms188048.aspx – Guffa 2014-11-16 01:49:49
啊是的,我明白你的意思了。所以將實現我的查詢不依賴於該設置。換句話說,使用IS NULL。我會發布一次,我有一個工程。 – sinDizzy 2014-11-16 02:39:57