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Microsoft KB Archive/103990

From BetaArchive Wiki

Article ID: 103990

Article Last Modified on 1/18/2007



APPLIES TO

  • Microsoft Access 1.0 Standard Edition
  • Microsoft Access 1.1 Standard Edition
  • Microsoft Access 2.0 Standard Edition
  • Microsoft Access 95 Standard Edition
  • Microsoft Access 97 Standard Edition



This article was previously published under Q103990

Novice: Requires knowledge of the user interface on single-user computers.


SYMPTOMS

An update query that tries to update more than one table may yield unexpected results.

RESOLUTION

You should not update more than one table in an update query.

STATUS

This behavior is by design.

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.

REFERENCES

For more information about update queries, search the Help Index for "update queries," or ask the Microsoft Access 97 Office Assistant.


Additional query words: action

Keywords: kbprb KB103990