Application.DFirst Method (Access)

發行項
10/12/2015

You can use the DFirst function to return a random record from a particular field in a table or query when you simply need any value from that field.

Syntax

expression .DFirst(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 from which you want to find the first or last value. It can be either a string expression identifying a field in a table or query, or 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.
Criteria	Optional	Variant	An optional string expression used to restrict the range of data on which the DFirst function is performed. For example, criteria is often equivalent to the WHERE clause in an SQL expression, without the wrd WHERE. If criteria is omitted, the DFirst function evaluates expr against the entire domain. Any field that is included in criteria must also be a field in domain; otherwise, the DFirst function returns a Null.

Return Value

Variant

Remarks

Note

If you want to return the first or last record in a set of records (a domain), you should create a query sorted as either ascending or descending and set the TopValues property to 1. From Visual Basic, you can also create an ADO Recordset object and use the MoveFirst or MoveLast method to return the first or last record in a set of records.

Example

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

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

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

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

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

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

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

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