ACC: Update Query on More Than One Table Gives Unexpected Data

MORE INFORMATION

If an update query in Microsoft Access is used to update two (or more) tables on the "many" side of a relationship, the resulting updated fields will be multiples of the updated value. Each value will be updated one time for each updated record in the corresponding table.

Steps to Reproduce Behavior

1. Create the following three tables:
   

         Table: Vendors
         -----------------
         Field Name: Name
            Data Type: Text
   
         Table: New Parts
         --------------------
         Field Name: Item
            Data Type: Text
         Field Name: Vendor
            Data Type: Text
         Field Name: Cost
            Data Type: Number
   
         Table: Rebuilt Parts
         --------------------
         Field Name: Item
            Data Type: Text
         Field Name: Vendor
            Data Type: Text
         Field Name: Cost
            Data Type: Number
   						

2. Add the following two records to the Vendors table:
   

         Name
         ----
         Bob
         Jill
   						

3. Enter the following three records to the New Parts table:
   

        Item       Vendor       Cost
        -----------------------------
        fender      Bob        100.00
        hood        Jill        50.00
        trunk       Bob        100.00
   						

4. Enter the following four records in the Rebuilt Parts table:
   

        Item       Vendor      Cost
        ----------------------------
        Pump        Bob        10.00
        Fan         Jill       45.00
        Pulley      Bob        20.00
        Piston      Bob        30.00
   						

5. Create the following query based on the three tables that you created above:
   

         Query:  Example Query
         ---------------------------------------------------
         Type: Update Query
         Join: [New Parts].[Vendor] <-> [Vendors].[Name]
         Join: [Rebuilt Parts].[Vendor] <-> [Vendors].[Name]
         Field: Name
            Table: Vendors
            Criteria: "Bob"
         Field: Cost
            Table: New Parts
            Update To: [New Parts].[Cost] * 2.0
         Field: Cost
            Table: Rebuilt Parts
            Update To: [Rebuilt Parts].[Cost] * 2.0
   						

6. Run the query, and then save and close it.
7. Open the Rebuilt Parts table.
   
   Note that the costs for items listing Bob as the vendor have been updated to four times their original values, rather than to two times as specified in the update query. Each updated record in the Rebuilt Parts table has been updated once for each updated record in the New Parts table.
8. Open the New Parts table.
   
   Note that the costs for items listing Bob as the vendor have been updated to eight times their original values, rather than to two times as specified in the update query. Each updated record in the New Parts table has been updated once for each updated record in the Rebuilt Parts table.

This effect is called a cross product (or Cartesian product), in which the values in Table B are updated one time for each item meeting the same criteria in Table A.