adding results of query against datatable to a column in another datatable in visual basic - sql

Question

Problem: I have populated a datatable using a query on a sql server database. The query is:
Select ID, startDate, codeID, Param,
(select top 1 startDate from myTable
where ID='" & ID & "' and Param = mt.param and codeID = 82 and startDate >= '" & startDate & "' and startDate >=mt.startDate
ORDER BY startDate)endTime,
from myTable mt where ID = '" & ID & "'
AND (startDate between '" & startDate & "' AND '" & endDate & "' AND (codeID = 81))
I want a new column called duration that will be the difference between endTime and startDate in milliseconds. I can't just add another subquery to the above query since the endTime column didn't exist until the subquery was ran.
So, is there a way to maybe run the first query to populate the datatable, then run a query like:
Select DateDiff(ms,endTime,startDate)
On its own and add its results to a new column in my datatable?

Answer 1

You can always nest that in another query:
select *, datediff(ms, startDate, endTime)
from (
<your existing query here>
) t
And while I'm here, it seems you need a lesson in parameterized queries:
Dim result As New DataTable
Dim Sql As String = _
"SELECT *, datediff(ms, startDate, endTime) FROM (" & _
"SELECT ID, startDate, codeID, Param, " & _
"(select top 1 startDate from myTable " & _
"where ID= #ID and Param = mt.param and codeID = 82 and startDate >= #startDate and startDate >=mt.startDate " & _
"ORDER BY startDate) endTime " & _
" FROM myTable mt " & _
" WHERE ID = #ID AND startDate between #startDate AND #endDate AND codeID = 81" & _
") t"
Using cn As New SqlConnection("connection string"), _
cmd As New SqlCommand(sql, cn)
cmd.Parameters.Add("#ID", SqlDbType.VarChar, 10).Value = ID
cmd.Parameters.Add("#startDate", SqlDbType.DateTime).Value = Convert.ToDateTime(startDate)
cmd.Parameters.Add("#endDate", SqlDbType.DateTime).Value = Convert.ToDateTime(endDate)
cn.Open()
Using rdr = cmd.ExecuteReader()
result.Load(rdr)
rdr.Close()
End Using
End Using