To quote the Access help file:
You can use the DMin and DMax functions to determine the minimum and maximum values in a specified set of records (a domain). Use the DMin and DMax functions in Visual Basic, a macro, a query expression, or a calculated control.
For example, you could use the DMin and DMax functions in calculated controls on a report to display the largest and smallest order amounts for a particular customer. Or you could use the DMin function in a query expression to display all orders with a discount greater than the minimum possible discount.
DMin(expr, domain[, criteria])
DMax(expr, domain[, criteria])
The DMin and DMax functions have the following arguments.
expr An expression that identifies the field for which you want to find the minimum or maximum value. 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.
domain A string expression identifying the set of records that constitutes the domain. It can be a table name or a query name.
criteria An optional string expression used to restrict the range of data on which the DMin or DMax 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 DMin and DMax functions evaluate expr against the entire domain. Any field that is included in criteria must also be a field in domain, otherwise the DMin and DMax functions returns a Null.
The DMin and DMax functions return the minimum and maximum values that satisfy criteria. If expr identifies numeric data, the DMin and DMax functions return numeric values. If expr identifies string data, they return the string that is first or last alphabetically.
The DMin and DMax functions ignore Null values in the field referenced by expr. However, if no record satisfies criteria or if domain contains no records, the DMin and DMax functions return a Null.
Whether you use the DMin or DMax function in a macro, module, query expression, or calculated control, you must construct the criteria argument carefully to ensure that it will be evaluated correctly.
You can use the DMin and DMax function to specify criteria in the Criteria row of a query, in a calculated field expression in a query, or in the Update To row of an update query.
Note You can use the DMin and DMax functions or the Min and Max functions in a calculated field expression in a totals query. If you use the DMin
or DMax function, values are evaluated before the data is grouped. If you use the Min or Max function, the data is grouped before values in the field expression are evaluated.
Use the DMin or DMax function in a calculated control when you need to specify criteria to restrict the range of data on which the function is performed. For example, to display the maximum freight charged for an order shipped to California, set the ControlSource property of a text box to the following expression:
=DMax("[Freight]", "Orders", "[ShipRegion] = 'CA'")
If you simply want to find the minimum or maximum value of all records in domain, use the Min or Max function.
You can use the DMin or DMax function in a module or macro or in a calculated control on a form if the field that you need to display is not in the record source on which your form is based.
Tip Although you can use the DMin or DMax function to find the minimum or maximum value from a field in a foreign table, it may be more efficient to create a query that contains the fields that you need from both tables, and base your form or report on that query.
Note Unsaved changes to records in domain aren't included when you use these functions. If you want the DMax or DMin function to be based on the changed values, you must first save the changes by clicking Save Record on the File menu, moving the focus to another record, or by using the Update method.
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