Application.DMax Method (Access)

项目
10/12/2015

You can use DMax function to determine maximum value in a specified set of records (a domain).

Syntax

expression .DMax(Expr, Domain, Criteria)

expression A variable that represents an Application object.

Parameters

Name	Required/Optional	Data Type	Description
Expr	Required	String	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 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	Required	String	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.
Criteria	Optional	Variant	An optional string expression used to restrict the range of data on which the 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 DMax function evaluates expr against the entire domain. Any field that is included in criteria must also be a field in domain, otherwise the DMax function returns a Null.

Return Value

Variant

Remarks

For example, you could use the DMax function in calculated controls on a report to display largest order amount for a particular customer.

The DMax function returns the maximum value that satisfy criteria. If expr identifies numeric data, the DMax function returns numeric values. If expr identifies string data, they return the string that is first or last alphabetically.

The DMax function ignores Null values in the field referenced by expr. However, if no record satisfies criteria or if domain contains no records, the DMax function returns a Null.

You can use the 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 DMax function or the Max function in a calculated field expression of a totals query. If you use the DMax function, values are evaluated before the data is grouped. If you use the Max function, the data is grouped before values in the field expression are evaluated.

Use the 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.

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.

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Sequential Numbering

Example

The following example returns the lowest and highest values from the Freight field for orders shipped to the United Kingdom. The domain is an Orders table. The criteria argument restricts the resulting set of records to those for which ShipCountry equals UK.

Dim curX As Currency 
Dim curY As Currency 
 
curX = DMin("[Freight]", "Orders", "[ShipCountry] = 'UK'") 
curY = DMax("[Freight]", "Orders", "[ShipCountry] = 'UK'")

In the next example, the criteria argument includes the current value of a text box called OrderDate. The text box is bound to an OrderDate field in an Orders table. Note that the reference to the control isn't included in the double quotation marks (") that denote the strings. This ensures that each time the DMax function is called, Microsoft Access obtains the current value from the control.

Dim curX As Currency 
curX = DMax("[Freight]", "Orders", "[OrderDate] = #" _ 
    & Forms!Orders!OrderDate & "#")

The following examples show how to use various types of criteria with the DMax function.

Sample code provided by: Community Member Icon The UtterAccess community | About the Contributors

    ' ***************************
    ' Typical Use
    ' Numerical values. Replace "number" with the number to use.
    variable = DMax("[FieldName]", "TableName", "[Criteria] = number")

    ' Strings.
    ' Numerical values. Replace "string" with the string to use.
    variable = DMax("[FieldName]", "TableName", "[Criteria]= 'string'")

    ' Dates. Replace "date" with the string to use.
    variable = DMax("[FieldName]", "TableName", "[Criteria]= #date#")
    ' ***************************

    ' ***************************
    ' Referring to a control on a form
    ' Numerical values
    variable = DMax("[FieldName]", "TableName", "[Criteria] = " & Forms!FormName!ControlName)

    ' Strings
    variable = DMax("[FieldName]", "TableName", "[Criteria] = '" & Forms!FormName!ControlName & "'")

    ' Dates
    variable = DMax("[FieldName]", "TableName", "[Criteria] = #" & Forms!FormName!ControlName & "#")
    ' ***************************

    ' ***************************
    ' Combinations
    ' Multiple types of criteria
    variable = DMax("[FieldName]", "TableName", "[Criteria1] = " & Forms![FormName]![Control1] _
             & " AND [Criteria2] = '" & Forms![FormName]![Control2] & "'" _
            & " AND [Criteria3] =#" & Forms![FormName]![Control3] & "#")
    
    ' Use two fields from a single record.
    variable = DMax("[LastName] & ', ' & [FirstName]", "tblPeople", "[PrimaryKey] = 7")
            
    ' Expressions
    variable = DMax("[Field1] + [Field2]", "tableName", "[PrimaryKey] = 7")
    
    ' Control Structures
    variable = DMax("IIf([LastName] Like 'Smith', 'True', 'False')", "tableName", "[PrimaryKey] = 7")
    ' ***************************

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