Facing difficulty in constructing SQL from multiple multi-select listboxes - oracle

Question

I have a form in which there are around 6 multiselect listBoxes. the listBoxes are populated from different tables. I have no problem in storing the selections from listBoxes in variables and then using the variables in a SQL query. the variable stores the selected item from listBox as follows:
If clientList.SelCount > 0 Then
For i = 0 To clientList.ListCount - 1
If clientList.Selected(i) Then
If Len(criteria_cl) = 0 Then
criteria_cl = Chr(39) & clientList.List(i) & Chr(39)
Else
criteria_cl = criteria_cl & "," & Chr(39) & clientList.List(i) & Chr(39)
End If
End If
Next
Else
End If
the SQL query is as follows with more variables which are called criteria_xx
strsql = "select * from pmt_hist_dmart_step2 where dbr_portfolio in (" & criteria_pf & ") and DBR_CLIENT in (" & criteria_cl & _
") and DBR_ACCT_TYPE in (" & criteria_ac & ")..... ;"
How do I deal with a situation when the user makes no selection. Currently, the criteria_xx variable becomes blank and the IN clause contains ('') and throws an error.
Please provide some advice on how to overcome this? If it were only two or three listBoxes, I would written different queries but this is six multiselect listBoxes and I have no clue.
Thanks in advance.

Answer 1

Here's one approach:
strsql = " select * " & _
" from pmt_hist_dmart_step2 " & _
" where " & iif(len(criteria_pf) = 0, _
"", _
"dbr_portfolio in (" & criteria_pf & ") and " _
) & _
iif(len(criteria_cl) = 0, _
"", _
"DBR_CLIENT in (" & criteria_cl & ") and " _
) & _
iif(len(criteria_ac) = 0, _
"", _
"DBR_ACCT_TYPE in (" & criteria_ac & ") and " _
) & _
... & _
" 1 = 1;"
The idea here is that each clause of the form dbr_portfolio in (...) should only be included if the ... is non-blank. iif is a built-in function that takes three arguments; if its first argument is true, then it returns its second argument, and if its first argument is false, then it returns its third argument. For example, iif(1 = 1, 5, 10) returns 5, and iif(1 = 2, 5, 10) returns 10. (N.B. The second and third arguments are both always evaluated, even though one of them is ignored afterward.)
Since something like where and or and and would not be valid SQL, I include each and within the iif-controlled code of the previous clause. Then, since a final and would not be valid SQL, I tacked on a final 1 = 1 clause that has no actual effect.
(By the way, sorry if my indentation scheme is ugly; it's been over a dozen years since I last wrote VB6, so I really don't remember how VB6 code is usually formatted.)