Error comparing datetime in SQL Server - sql-server

Question

I'm currently writing this program that the user will input the start date and end date. Then the program will retrieve the records from the database where the startdate in db will be >= user input start date and enddate in db will be <= user input end date.
Dim dateStr As DateTime = dtpStart.Value
Dim dateEnd As DateTime = dtpEnd.Value
MsgBox(dateStr)
con.ConnectionString = "Data Source=MKZSA065\SQLSERVER2008R2,1499;Initial Catalog=inv"
con.Open()
MsgBox("server connected")
cmd.Connection = con
'cmd.CommandText = "Select column_name as 'Columnname', data_type as'Datatype' from information_schema.columns where table_name = 'inv.dbo.InOutTransaction' AND column_name = 'inv.dbo.InOutTransaction.startDate'"
'cmd.CommandText = "Select inv.dbo.InOutTransaction.refNo, inv.dbo.Case_Status.deployedBy, CONVERT(varchar(10), inv.dbo.InOutTransaction.startDate, 120) as startDate, CONVERT(varchar(10), inv.dbo.InOutTransaction.endDate, 120) as endDate, inv.dbo.InOutTransaction.item FROM inv.dbo.InOutTransaction inner join inv.dbo.Case_Status ON inv.dbo.InOutTransaction.refNo = inv.dbo.Case_Status.refNo WHERE inv.dbo.InOutTransaction.refNo LIKE 'L%' AND inv.dbo.InOutTransaction.status LIKE 'Out'"
cmd.CommandText = "Select inv.dbo.InOutTransaction.refNo, inv.dbo.Case_Status.deployedBy, CONVERT(varchar(10),inv.dbo.InOutTransaction.startDate,120) as startDate, CONVERT(varchar(10),inv.dbo.InOutTransaction.endDate,120) as endDate, inv.dbo.InOutTransaction.item from inv.dbo.InOutTransaction inner join inv.dbo.Case_Status ON inv.dbo.InOutTransaction.refNo = inv.dbo.Case_Status.refNo WHERE inv.dbo.InOutTransaction.refNo LIKE 'L%' AND inv.dbo.InOutTransaction.status LIKE '%Out%' AND inv.dbo.InOutTransaction.startDate >= '" & dateStr & "' AND inv.dbo.InOutTransaction.endDate <= '" & dateEnd & "'"
Dim lrd As SqlDataReader
Dim li As ListViewItem
lrd = cmd.ExecuteReader()
Dim num As Integer = 1
While lrd.Read()
ListView1.BeginUpdate()
li = ListView1.Items.Add(num.ToString)
li.SubItems.Add(lrd("refNo").ToString)
li.SubItems.Add(lrd("deployedBy").ToString)
li.SubItems.Add(lrd("startDate").ToString)
li.SubItems.Add(lrd("endDate").ToString)
li.SubItems.Add(lrd("item").ToString)
'li.SubItems.Add(lrd("column_name").ToString)
'li.SubItems.Add(lrd("data_type").ToString)
num += 1
ListView1.EndUpdate()
ListView1.EnsureVisible(ListView1.Items.Count - 1)
End While
There was an error
Conversion failed when converting datetime from character string
How and what should I do :(

Answer 1

USE PARAMETERISED QUERIES
Sorry to yell, but I cannot stress enough how important this is, not just to resolve your error, but for performance, and security of your application in general.
So instead of
"inv.dbo.InOutTransaction.startDate >= '" & dateStr & "' AND inv.dbo.InOutTransaction.endDate <= '" & dateEnd & "'"
You need to use
"inv.dbo.InOutTransaction.startDate >= #StartDate AND inv.dbo.InOutTransaction.endDate <= #EndDate"
Then add the parameters to your SqlCommand:
cmd.Parameters.Add("#StartDate", SqlDbType.DateTime).Value = dateStr
cmd.Parameters.Add("#EndDate", SqlDbType.DateTime).Value = dateEnd
This means that there is no need for any implicit conversions, your SqlCommand is expecting two date parameters, and you pass two DateTime objects. All of a sudden the format of the dates, and cultural variations is irrelevant. Furthermore, it means that SQL Server can make use of cached plans and does not need to recompile the query for every different start and end date values passed.
As an aside, it is a good idea to use Using when dealing with IDisposable objects, especially with unmanaged objects like these. So you might end up with something like:
Dim dateStr As DateTime = dtpStart.Value
Dim dateEnd As DateTime = dtpEnd.Value
Dim sql as String = "Select inv.dbo.InOutTransaction.refNo, " & _
" inv.dbo.Case_Status.deployedBy, " & _
" CONVERT(varchar(10), " & _
" inv.dbo.InOutTransaction.startDate,120) as startDate, " & _
" CONVERT(varchar(10),inv.dbo.InOutTransaction.endDate,120) as endDate, " & _
" inv.dbo.InOutTransaction.item " & _
"from inv.dbo.InOutTransaction "
" inner join inv.dbo.Case_Status " & _
" ON inv.dbo.InOutTransaction.refNo = inv.dbo.Case_Status.refNo " & _
"WHERE inv.dbo.InOutTransaction.refNo LIKE 'L%' " & _
"AND inv.dbo.InOutTransaction.status LIKE '%Out%' " & _
"AND inv.dbo.InOutTransaction.startDate >= #StartDate " & _
"AND inv.dbo.InOutTransaction.endDate <= #EndDate"
Using con As new SqlConnection("Data Source=MKZSA065\SQLSERVER2008R2,1499;Initial Catalog=inv;User ID=inv_admin;Password=inv_admin123")
Using cmd As New SqlCommand(sql, con)
con.Open()
cmd.Parameters.Add("#StartDate", SqlDbType.DateTime).Value = dateStr
cmd.Parameters.Add("#EndDate", SqlDbType.DateTime).Value = dateEnd
Using lrd As SqlDataReader = cmd.ExecuteReader()
Dim num As Integer = 1
Dim li As ListViewItem
While lrd.Read()
ListView1.BeginUpdate()
li = ListView1.Items.Add(num.ToString)
li.SubItems.Add(lrd("refNo").ToString)
li.SubItems.Add(lrd("deployedBy").ToString)
li.SubItems.Add(lrd("startDate").ToString)
li.SubItems.Add(lrd("endDate").ToString)
li.SubItems.Add(lrd("item").ToString)
'li.SubItems.Add(lrd("column_name").ToString)
'li.SubItems.Add(lrd("data_type").ToString)
num += 1
ListView1.EndUpdate()
ListView1.EnsureVisible(ListView1.Items.Count - 1)
End While
End Using
End Using
Please forgive my vb.Net if it is littered with errors, I haven't used it in a long time so am rusty to say the least, hopefully it is good enough to get the point across though

Answer 2

I would imagine the the datestr is in a local format.
Use the format YYYYMMDD as that is consistent regardless of DATEFORMAT settings.