You can use the DAvg function to calculate the average of a set of values in a specified set of records (a domain). Use the DAvg function in a Visual Basic for Applications (VBA) module, in a macro, in a query expression, or in a calculated control.
For example, you could use the DAvg function in the criteria row of a select query on freight cost to restrict the results to those records where the freight cost exceeds the average. Or you could use an expression including the DAvg function in a calculated control and display the average value of previous orders next to the value of a new order.
DAvg ( expr , domain [, criteria] )
The DAvg function syntax has these arguments:
Required. An expression that identifies the field containing the numeric data you want to average. It can be a string expression identifying a field in a table or query, or it can be an expression that performs a calculation on data in that field. In expr, you can include the name of a field in a table, a control on a form, a constant, or a function. If expr includes a function, it can be either built-in or user-defined, but not another domain aggregate or SQL aggregate function.
Required. A string expression identifying the set of records that constitutes the domain. It can be a table name or a query name for a query that does not require a parameter.
Optional. A string expression used to restrict the range of data on which the DAvg function is performed. For example, criteria is often equivalent to the WHERE clause in an SQL expression, without the word WHERE. If criteria is omitted, the DAvg function evaluates expr against the entire domain. Any field that is included in criteria must also be a field in domain; otherwise the DAvg function returns a Null.
Records containing Null values aren't included in the calculation of the average.
Whether you use the DAvg function in a macro or module, in a query expression, or in a calculated control, you must construct the criteria argument carefully to ensure that it will be evaluated correctly.
You can use the DAvg function to specify criteria in the Criteria row of a query. For example, suppose you want to view a list of all products ordered in quantities above the average order quantity. You could create a query on the Orders, Order Details, and Products tables, and include the Product Name field and the Quantity field, with the following expression in the Criteria row beneath the Quantity field:
You can also use the DAvg function within a calculated field expression in a query, or in the Update To row of an update query.
Note: You can use either the DAvg or Avg function in a calculated field expression in a totals query. If you use the DAvg function, values are averaged before the data is grouped. If you use the Avg function, the data is grouped before values in the field expression are averaged.
Use the DAvg function in a calculated control when you need to specify criteria to restrict the range of data on which the DAvg function is performed. For example, to display the average cost of freight for shipments sent to California, set the ControlSource property of a text box to the following expression:
=DAvg("[Freight]", "Orders", "[ShipRegion] = 'CA'")
If you simply want to average all records in domain, use the Avg function.
You can use the DAvg function in a module or macro or in a calculated control on a form if a field that you need to display isn't in the record source on which your form is based. For example, suppose you have a form based on the Orders table, and you want to include the Quantity field from the Order Details table in order to display the average number of items ordered by a particular customer. You can use the DAvg function to perform this calculation and display the data on your form.
If you use the DAvg function in a calculated control, you may want to place the control on the form header or footer so that the value for this control is not recalculated each time you move to a new record.
If the data type of the field from which expr is derived is a number, the DAvg function returns a Double data type. If you use the DAvg function in a calculated control, include a data type conversion function in the expression to improve performance.
Although you can use the DAvg function to determine the average of values in a field in a foreign table, it may be more efficient to create a query that contains all of the fields that you need and then base your form or report on that query.
Note: Unsaved changes to records in domain aren't included when you use this function. If you want the DAvg function to be based on the changed values, you must first save the changes by clicking Save Record under Records on the Data tab, moving the focus to another record, or by using the Update method.
Note: Examples that follow demonstrate the use of this function in a Visual Basic for Applications (VBA) module. For more information about working with VBA, select Developer Reference in the drop-down list next to Search and enter one or more terms in the search box.
The following function returns the average freight cost for orders shipped on or after a given date. The domain is an Orders table. The criteria argument restricts the resulting set of records based on the given country/region and ship date. Note that the keyword AND is included in the string to separate the multiple fields in the criteria argument. All records included in the DAvg function calculation will have both of these criteria.
Public Function AvgFreightCost _
(ByVal strCountryRegion As String, _
ByVal dteShipDate As Date) As Double
AvgFreightCost = DAvg("[Freight]", "Orders", _
"[ShipCountryRegion] = '" & strCountryRegion & _
"'AND [ShippedDate] >= #" & dteShipDate & "#")
To call the function, use the following line of code in the Immediate window:
:AvgFreightCost "UK", #1/1/96#