Passing Nulls from Excel to SQL - sql

Question

I'm using a VBA Script to update a table in SQL, so far it works perfectly. The problem is when handling null values. Because the VBA script loops until the first column ends, some values are null in the worksheet, but they are placed as zeros in sql.
In Excel:
Name Last name Age
daniel mtz 22
jose mtz 25
John doe
Final result in SQL:
Name Last name Age
daniel mtz 22
jose mtz 25
John doe 0
Any thoughts on how I can tell the Macro or SQL to read them as null and not zero?
P.S, programming each column in sql to place null in the corresponding value is not an option, because this table will be changing constantly and I could have all columns filled, or just some, etc.
[UPDATE] Here is the code for the VBA:
Sub Macro_CargarSQL()
'VARIABLES
Dim conn As New ADODB.Connection
Dim iRowNo As Integer
'Column variables
Dim sname, slastname, sage As String
'CONECTION TO SERVER Y BD
conn.Open "Provider=SQLOLEDB;Data Source=Termxgesvsql07\vfsitesamn;Initial Catalog=DW_PLCO;Integrated Security=SSPI;"
'Import into SQL
With Sheets("test")
'Start row 2
iRowNo = 2
'Delete previous
conn.Execute "delete from table"
'Loop for insert
Do Until .Cells(iRowNo, 1) = ""
sname = .Cells(iRowNo, 1)
slastname = .Cells(iRowNo, 2)
sage = .Cells(iRowNo, 3)
conn.Execute "insert into dbo.table (name, lastname,age ) values ('" & sname & "', '" & slastname & "', '" & sage & "')"
iRowNo = iRowNo + 1
Loop
End With
conn.Close
Set conn = Nothing
End Sub

Answer 1

One way I've done this is to create two SQL strings and do checks on the actually values.
You can do this as follows (generally this is a lot easier if you have an array as you can write an iteration through your values/fieldnames).
Do Until .Cells(iRowNo, 1) = ""
sName = .Cells(iRowNo, 1)
slastname = .Cells(iRowNo, 2)
sage = .Cells(iRowNo, 3)
Dim sqlStrStart As String
Dim sqlStrValues As String
Dim sqlStrFull As String
sqlStrStart = "insert into dbo.table ("
sqlStrValues = " values ("
'build string dynamically (generally I do this using parameters, but this will work)
If sName <> "" Then
sqlStrStart = sqlStrStart + "name,"
sqlStrValues = sqlStrValues + sName & ","
End If
If slastname <> "" Then
sqlStrStart = sqlStrStart + "lastname,"
sqlStrValues = sqlStrValues + slastname & ","
End If
If sName <> "" Then
sqlStrStart = sqlStrStart + "age,"
sqlStrValues = sqlStrValues + sage & ","
End If
'remove last comma
sqlStrStart = Left(sqlStrStart, Len(sqlStrStart) - 1)
sqlStrValues = Left(sqlStrValues, Len(sqlStrValues) - 1)
'close parenthesis
sqlStrStart = sqlStrStart & ")"
sqlStrValues = sqlStrValues & ")"
'combine
sqlStrFull = sqlStrStart + sqlStrValues + ";"
conn.Execute sqlStrFull
iRowNo = iRowNo + 1
Loop

Answer 2

The best way is to create a function that inspects whether a cell value is empty or not. When empty, output should be "null", but when not, enclose the value in between single quotes.
This function can also be used so you can escape values that has single quote in it (such as "O'Brien"). Otherwise, in your current code, you'll encounter a SQL error.
Here's the function:
Function toSQL(s)
If s = "" Then toSQL = "null" Else toSQL = "'" & Replace(s, "'", "''") & "'"
End Function
And here's the replacement Insert statement:
conn.Execute "insert into dbo.table (name, lastname,age ) values (" & toSQL(sname) & ", " & toSQL(slastname) & ", " & toSQL(sage) & ")"
If you consistently call the toSQL function, and also consistently define the column in the SQL database as nullable, you'll be set. If the data type is numeric, you may not want to call toSQL though.

Answer 3

Use this when setting a null value in Excel VBA, and pass that to the SQL parameter's value.
DBNull.Value