ACC: Adding Dynamic Counter to Query to Count Records

• Microsoft Access versions 1.0, 1.1, 2.0, 7.0, 97

SUMMARY

Advanced: Requires expert coding, interoperability, and multiuser skills.

This article describes how to use a dynamic counter value in a query field for the following purposes:

• Returning the top x number of records to ship in a Microsoft Access version 1.x query.

  NOTE: In Microsoft Access versions 2.0, 7.0, and 97, you can use the TopValues query property to accomplish this.

• Displaying the record's position number on a form. For more information about this topic, query on the following words here in the Microsoft Knowledge base:

        record and position and number and form
  

• Printing the top x number of records on a report. For more information about this topic, query on the following words here in the Microsoft Knowledge Base:

        top and 10 and records and report
  

  NOTE: If the report includes totals, totals will be displayed for all the records, not just the top x number of records. To total only the top x number of records, limit the records included in the report using the method described later in this article.

MORE INFORMATION

Sample code to implement a dynamic counter is described later in this article. There are several limitations to this method, including the following:

• You must reset the global counter to 0 before you run the query each time. You can use the function SetToZero() to do this.
• Any scrolling, minimizing, maximizing, switching focus away and back, and so on, causes a repaint to occur, which in turn causes the query to call the function again. For this reason, you should not use this function in a select query. Instead, you should base a report on the select query or run a make-table query and view the resulting table.
• When basing a report on a select query with this function, scrolling back through the pages will cause the function to be called multiple times, and the counter expression will be off by the total number of records in the recordset.
• When you place criteria on the counter expression, the function will be called twice per record. For example, if you specify criteria of <=10 to return the first 10 records, the recordset will contain 10 records, but the counter expression will be off by the total number of records in the recordset.
• Do not place the counter expression in the first column of the query; the number will be off by one.
• Do not combine criteria and sorting in a query with the counter expression. The criteria will be applied before the sort. Instead, you must create a make-table query with the sort, and then base a second query containing the counter expression on the new table with sorted data.

The Dynamic Counter Function

The following Access Basic functions, Qcntr() and SetToZero(), can be used to implement a dynamic counter in a query. To use the Access Basic functions do the following:

1. Create a new module.

2. Type the following declarations in the Global Declarations section:

         ' Global Declarations Section.
          Option Explicit
          Global Cntr
   

3. Type the following functions in the module:

       '*************************************************************
       ' Function:  Qcntr()
       '
       ' Purpose: This function will increment and return a dynamic
       ' counter. This function should be called from a query.
       '*************************************************************
   

        Function QCntr(x) As Long
           Cntr = Cntr + 1
           QCntr = Cntr
        End Function
   
       '**************************************************************
       ' Function:  SetToZero()
       '
       ' Purpose: This function will reset the global Cntr to 0. This
       ' function should be called each time before running a query
       ' containing the Qcntr() function.
       '**************************************************************
   
        Function SetToZero()
           Cntr = 0
        End Function
   
   

Returning the Top X Records

To return the 10 most expensive orders to ship, follow these steps:

1. Open the sample Northwind database (In Access 1.x and 2.0, called NWIND.MDB and in all other versions, Northwind.mdb).

2. Create a new query based on the Orders table. Include the following fields:

         Field: Order ID
         Field: Customer ID
         Field: Order Date
         Field: Freight
            Sort: Descending
         Field: Expr1: Qcntr([order id])
   
   

3. From the Query menu, choose Make Table. When you are prompted for a table name, type "Sorted Orders" (without the quotation marks).

4. Save the query as Make Sorted Orders.

5. Create a new query that will be based on the Sorted Orders table after it is created. For now, close the Add Table dialog box without adding a table to the query. From the view menu, choose SQL, and then enter the following SQL statement:

         Select * from [Sorted Orders] where [Expr1] <= 10
   

6. Save this query as Top 10 Orders, and then close it.

7. Create the following macro:

         Actions
         -----------
         RunCode
         SetWarnings
         OpenQuery
         OpenQuery
   

         Macro Actions
         -----------------------------------
         RunCode
            Function Name: SetToZero()
         SetWarnings
            Warnings On: No
         OpenQuery
            Query Name: [Make Sorted Orders]
         OpenQuery
            Query Name: [Top 10 Orders]
   
   

8. Run the macro. The table Sorted Orders will be created, and then the Top 10 Orders query will be displayed.

Creating a Top 10 Report That Includes Totals

To create a Top 10 Report that includes totals, follow these steps:

1. Repeat steps 1-5 in the above section.

2. Create a new report called Top 10 Orders based on the Top 10 Orders query.

3. Create the following new macro:

         Actions
         -----------
         RunCode
         SetWarnings
         OpenQuery
         OpenReport
   

         Macro Actions
         -----------------------------------
         RunCode
            Function Name: SetToZero()
         SetWarnings
            Warnings On: No
         OpenQuery
            Query Name: [Make Sorted Orders]
         OpenReport
            Report Name: [Top 10 Orders]
   
   

4. Run the macro.

REFERENCES

For information about when functions are executed in queries, please see the following article in the Microsoft Knowledge Base:

    ARTICLE-ID: Q98788
    TITLE     : ACC: Number of Times a Custom Function Executes in a Query

Keywords          : QryOthr kbusage
Version           : 1.0 1.1 2.0
Platform          : WINDOWS
Hardware          : x86
Issue type        : kbhowto