这段代码真的让我发疯。
今天早些时候，在这个很棒的论坛上，我得到了使用以下代码将初始默认值加载到数据库中的帮助。
s = "INSERT INTO tblTrainings (CourseId, tblLocations.LocationId, dateId,AvailableSeats) (SELECT @CosID, @LocID, @dat,Seating_Capacity FROM tblLocations, tblCourses WHERE tblCourses.locationId= tblLocations.LocationId and courseId = @cosId and tblLocations.locationID=@LocID)"
s += "UPDATE tblTrainings SET AvailableSeats = AvailableSeats - 1 WHERE CourseID = @cosID AND LocationID = @locId AND dateId = @dat"
历史：
我有一个包含几行记录的 dataList 和一个链接，上面写着“单击此处注册。
当您将鼠标悬停在此链接上时，它会显示日期、课程、位置的 ID。
当用户单击该链接时，if 检查数据库以查看 dateId、CourseId、LocationId 和 AvailableSeats 是否为空。
问题：
我在上述解决方案中遇到的问题是，每次用户点击注册链接时，都会更新现有记录。这很好，但同时，一条新记录被插入到数据库中，这并不好。
因此，我决定先进行检查。
检查数据库中是否存在满足某些条件的记录（在下面的 SELECT 语句中指定）
如果availableSeats (RemainingSeates) 为null，dateId 为null，courseid 为null，locationid 为null，则执行INSERT 语句。
如果它们不为空，则执行 UPDATE 语句。
到目前为止我做了什么并不重要，只执行 UPDATE 语句。
任何想法如何解决这个问题？
下面是我正在使用的代码：
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
Dim username = Session.Item("Username").ToString
Dim connStr As String = ConfigurationManager.ConnectionStrings("DBConnectionString").ConnectionString
Dim conn As New SqlConnection(connStr)
Try
Dim s As String
Dim counter As Integer
'If AvailableSeats already saved, then don't do an INSERT
s = "SELECT Count(*) Counter FROM tblTrainings WHERE AvailableSeats Is Null and CourseId is null and LocationId is null and dateId is null"
'Response.Write(s)
'Response.End()
Dim connSt As String = ConfigurationManager.ConnectionStrings("DBConnectionString").ConnectionString
Dim connc As New SqlConnection(connSt)
Dim cmdc As New SqlCommand(s, connc)
connc.Open()
cmdc.ExecuteNonQuery()
counter = cmdc.ExecuteScalar()
' Now let's see if we found existing record
If counter > 0 Then
s = "INSERT INTO tblTrainings (CourseId, tblLocations.LocationId, dateId,AvailableSeats) (SELECT @CosID, @LocID, @dat,Seating_Capacity FROM tblLocations, tblCourses WHERE tblCourses.locationId= tblLocations.LocationId and courseId = @cosId and tblLocations.locationID=@LocID)"
s += "UPDATE tblTrainings SET AvailableSeats = AvailableSeats - 1 WHERE CourseID = @cosID AND LocationID = @locId AND dateId = @dat"
Else
s += "UPDATE tblTrainings SET AvailableSeats = AvailableSeats - 1 WHERE CourseID = @cosID AND LocationID = @locId AND dateId = @dat"
End If
Response.Write(s)
Response.End()
Dim cmd = New SqlCommand(s, conn)
cmd.Parameters.AddWithValue("@cosID", Request.QueryString("cosId"))
cmd.Parameters.AddWithValue("@locID", Request.QueryString("locid"))
cmd.Parameters.AddWithValue("@dat", Request.QueryString("iddate"))
conn.Open()
cmd.ExecuteNonQuery()
conn.Close()
'Display some feedback to the user to let them know it was processed
Label1.ForeColor = System.Drawing.Color.Green
Label1.Text = "Record successfully saved!"
Catch
'If the message failed at some point, let the user know
Label1.ForeColor = System.Drawing.Color.Red
Label1.Text = "Your record failed to save, please try again."
End Try
End Sub
s = "IF EXISTS (SELECT TrainingId FROM tblTrainings WHERE AvailableSeats Is NOT NULL and CourseId is NOT NULL and LocationId is NOT NULL and dateId is NOT NULL) "
s += " BEGIN " '***Record already exists in the tblTrainings table, update existing record instead instead***
s += "UPDATE tblTrainings SET AvailableSeats = AvailableSeats - 1 WHERE CourseID = @cosID AND LocationID = @locId AND dateId = @dat "
s += " End "
s += " ELSE "
s += " BEGIN " '***No record exists in the tblTrainings table; create one and update it at same time.***
s += " INSERT INTO tblTrainings (CourseId, tblLocations.LocationId, dateId,AvailableSeats) (SELECT @CosID, @LocID, @dat,Seating_Capacity FROM tblLocations, tblCourses WHERE tblCourses.locationId= tblLocations.LocationId and courseId = @cosId and tblLocations.locationID=@LocID)"
s += "UPDATE tblTrainings SET AvailableSeats = AvailableSeats - 1 WHERE CourseID = @cosID AND LocationID = @locId AND dateId = @dat"
s += " End "