UPDATE query not using WHERE clause - sql

Question

I am trying to use an UPDATE query to modify a field in a table from a field in another table.
The query statement I'm using is:
UPDATE Todays_Deliveries SET Remaining = DLookup("Remaining","Current_Delivery","[MP-Ref] = Form![MP-Ref] And [Cat No] ='" & [Cat No] & "'")
WHERE "[MP-Ref] = Form![MP-Ref] And [Cat No] ='" & [Cat No] & "'";
MP-Ref is the delivery reference.
Cat No is the item reference.
Where Todays_Deliveries is a table with the total records related to items coming in from deliveries on a given day. The user selects a delivery using a form which then uses an APPEND query to populate the Current_Delivery table based on the delivery reference. Once the user is finished the Current_Delivery table is cleared using a DELETE query.
Both tables have a Remaining value with the total number of a particular record that still needs to be booked in. The query updates the Todays_Deliveries table when the user modifies the Remaining field of the Current_Delivery on the Current_Delivery form. Everything works fine but any records that aren't in the Current_Delivery table when the query is run are updated to NULL.
Removing the WHERE clause seems to have no impact on the results, which leads me to believe I am not utalising the WHERE clause correctly.
Any help/advice would be greatly appreciated.

Answer 1

Your whole Where clause is enclosed within double-quotes.
That is a bit odd even for Ms Access.
Try this :
UPDATE Todays_Deliveries
SET Remaining = DLookup("Remaining","Current_Delivery","[MP-Ref] = Form![MP-Ref] And [Cat No] ='" & [Cat No] & "'")
WHERE [MP-Ref] = Form![MP-Ref] And [Cat No] = "'" & [Cat No] & "'";