Application.DCount Method (Access)

项目
10/12/2015

You can use the DCount function to determine the number of records that are in a specified set of records (a domain).

Syntax

expression .DCount(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 count records. 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	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 DCount 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 DCount function evaluates expr against the entire domain. Any field that is included in criteria must also be a field in domain; otherwise the DCount function returns a Null.

Return Value

Variant

Remarks

For example, you could use the DCount function in a module to return the number of records in an Orders table that correspond to orders placed on a particular date.

Use the DCount function to count the number of records in a domain when you don't need to know their particular values. Although the expr argument can perform a calculation on a field, the DCount function simply tallies the number of records. The value of any calculation performed by expr is unavailable.

Use the DCount 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 number of orders to be shipped to California, set the ControlSource property of a text box to the following expression:

=DCount("[OrderID]", "Orders", "[ShipRegion] = 'CA'")

If you simply want to count all records in domain without specifying any restrictions, use the Count function.

The Count function has been optimized to speed counting of records in queries. Use the Count function in a query expression instead of the DCount function, and set optional criteria to enforce any restrictions on the results. Use the DCount function when you must count records in a domain from within a code module or macro, or in a calculated control.

You can use the DCount function to count the number of records containing a particular field that isn't in the record source on which your form or report is based. For example, you could display the number of orders in the Orders table in a calculated control on a form based on the Products table.

The DCount function doesn't count records that contain Null values in the field referenced by expr unless expr is the asterisk (*) wildcard character. If you use an asterisk, the DCount function calculates the total number of records, including those that contain Null fields. The following example calculates the number of records in an Orders table.

intX = DCount("*", "Orders")

If domain is a table with a primary key, you can also count the total number of records by setting expr to the primary key field, since there will never be a Null in the primary key field.

If expr identifies multiple fields, separate the field names with a concatenation operator, either an ampersand (&) or the addition operator (+). If you use an ampersand to separate the fields, the DCount function returns the number of records containing data in any of the listed fields. If you use the addition operator, the DCount function returns only the number of records containing data in all of the listed fields. The following example demonstrates the effects of each operator when used with a field that contains data in all records (ShipName) and a field that contains no data (ShipRegion).

intW = DCount("[ShipName]", "Orders") 
intX = DCount("[ShipRegion]", "Orders") 
intY = DCount("[ShipName] + [ShipRegion]", "Orders") 
intZ = DCount("[ShipName] & [ShipRegion]", "Orders")

Note

The ampersand is the preferred operator for performing string concatenation. You should avoid using the addition operator for anything other than numeric addition, unless you specifically wish to propagate Nulls through an expression.

Example

The following function returns the number of orders shipped to a specified country or region after a specified ship date. The domain is an Orders table.

Public Function OrdersCount(ByVal strCountry As String, _ 
                            ByVal dteShipDate As Date) As Integer 
 
    OrdersCount = DCount("[ShippedDate]", "Orders", _ 
                  "[ShipCountry] = '" & strCountry & _ 
                  "' AND [ShippedDate] > #" & dteShipDate & "#") 
End Function

The following examples show how to use various types of criteria with the DCount 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 = DCount("[FieldName]", "TableName", "[Criteria] = number")

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

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

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

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

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

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

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