pick value from listbox and use in sql query as column name.query dynamically pick column name from variable

Question

I have VB.net app that when run you select from listbox values that should then be used in select query.Then click save command button. see vb code snippet below

transport = lsttrans.SelectedItem
    leave = lstleave.SelectedItem

then query like below.Note transport and leave are dummy columns not on existing employee table.

select employeeid,'' as transport_allowance,'' as leave from employees

i wish to somehow create new query to be something close to the below using my selected values in listbox.

select employeeid,transport,leave from employees

Answer 1

Use String.Format(). Here is the example assuming transport and leave variables are already declared:

Dim myQueryTemplate As String = "SELECT employeeid, {0}, {1} FROM employees"
Dim myFinalQuery as String = String.Format(myQueryTemplate, transport, leave)

If you will debug that, the value of myFinalQuery will be:

"SELECT employeeid, transport, leave FROM employees"

Add more if needed. From my given example, the next parameter will be {2} and so on.

Answer 2

Do you already know how to retrieve data from a database in VB.NET? If not then you should read up on ADO.NET.

Assuming that you know how ADO.NET works, your SQL is simply a String, so you can build it up from parts the same way you can any other String. In this case, I would suggest calling the String.Format method to insert the column names into a query template.