Using a boolean function after where (SQL)? - sql

Question

I'm trying to use a function that results a boolean after in a where in a SQL statement.
What the function does is that it verifies if the selected date is within two const dates and results a boolean. I'm having problem with the SQL syntax
Sqlstring = "Select count() from [Orders].[Date]" & _
where " & Function([Orders].[Date]) = True & ""
I'm not sure if the sql statement is correct.
Edit here's the code:
public StartDate as String
public EndDate As string
Private Function GetOrdersNumbers() As Integer
Dim rsData As ADODB.RecordSet
Dim szConnect As String
Dim szSQL As String
Dim DataSource As String
DataSource = "C:\Users\user\Desktop\db.mdb"
szConnect = "Provider=Microsoft.Jet.OLEBD.4.0;" & _
"Data Source=" & DataSource & ";" & _
"user ID=admin;password=;"
szSQL = "SELECT COUNT(*) FROM [Et_Journal Livraison Fournisseur] WHERE [Et_Journal Livraison Fournisseur].[Date] BETWEEN [#StartDate] And [#EndDate] "
Set rsData = New ADODB.RecordSet
rsData.Open szSQL, szConnect, adOpenForwardOnly, adLockReadOnly, adCmdText
If Not rsData.EOF Then
Range("A01").CopyFromRecordset RecordSet
GetOrdersNumbers = CInt(Range("A01").Value)
End If
End Function

Answer 1

You did not provide information about database engine... Nevertheless
I'd suggest to use query like this:
SELECT COUNT(*)
FROM Orders
WHERE [Date] BETWEEN [#date1] AND [#date2]
where
#date1 and #date1 is a parameter
There's no reason to use function.
[EDIT]
Thank you for clarification. Have a look at below code:
Option Explicit
Sub Test()
Dim d1 As Date
Dim d2 As Date
d2 = DateSerial(2015, 1, 6)
d1 = DateAdd("MM", -3, d2)
MsgBox GetOrdersNumbers(d1, d2)
End Sub
Function GetOrdersNumbers(ByVal StartDate As Date, ByVal EndDate As Date) As Long
Dim oConn As ADODB.Connection, oRst As ADODB.Recordset
Dim sConnString As String, sQry As String
Dim retVal As Long
sConnString = "Provider=Microsoft.Jet.OLEBD.4.0;" & _
"Data Source=C:\Users\user\Desktop\db.mdb;" & _
"user ID=admin;password=;"
Set oConn = New ADODB.Connection
With oConn
.ConnectionString = sConnString
.Open
End With
sQry = "SELECT [Date] As MyDate" & vbCr & _
"FROM [Et_Journal Livraison Fournisseur]" & vbCr & _
"WHERE [Et_Journal Livraison Fournisseur].[Date] BETWEEN #" & StartDate & "# And #" & EndDate & "#"
Set rsData = New ADODB.Recordset
oRst.Open szSQL, oConn, adOpenStatic, adLockReadOnly
retVal = oRst.RecordCount
End If
Exit_GetOrdersNumbers:
On Error Resume Next
oRst.Close
Set oRst = Nothing
oConn.Close
Set oConn = Nothing
GetOrdersNumbers = retVal
Exit Function
Err_GetOrdersNumbers:
MsgBox Err.Description, vbExclamation, Err.Number
Resume Exit_GetOrdersNumbers
End Function