Application.DLookup Method (Access)

Articolo
10/12/2015

You can use the DLookup function to get the value of a particular field from a specified set of records (a domain).

Syntax

expression .DLookup(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 whose value you want to return. 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 DLookup 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 DLookup function evaluates expr against the entire domain. Any field that is included in criteria must also be a field in domain; otherwise, the DLookup function returns a Null.

Return Value

Variant

Remarks

You can use the DLookup function to display the value of a field that isn't in the record source for your form or report. For example, suppose you have a form based on an Order Details table. The form displays the OrderID, ProductID, UnitPrice, Quantity, and Discount fields. However, the ProductName field is in another table, the Products table. You could use the DLookup function in a calculated control to display the ProductName on the same form.

The DLookup function returns a single field value based on the information specified in criteria. Although criteria is an optional argument, if you don't supply a value for criteria, the DLookup function returns a random value in the domain.

If no record satisfies criteria or if domain contains no records, the DLookup function returns a Null.

If more than one field meets criteria, the DLookup function returns the first occurrence. You should specify criteria that will ensure that the field value returned by the DLookup function is unique. You may want to use a primary key value for your criteria, such as [EmployeeID] in the following example, to ensure that the DLookup function returns a unique value:

Dim varX As Variant 
varX = DLookup("[LastName]", "Employees", "[EmployeeID] = 1")

Whether you use the DLookup function in a macro or module, a query expression, or a calculated control, you must construct the criteria argument carefully to ensure that it will be evaluated correctly.

You can use the DLookup function to specify criteria in the Criteria row of a query, within a calculated field expression in a query, or in the Update To row in an update query.

You can also use the DLookup function in an expression in a calculated control on a form or report if the field that you need to display isn't in the record source on which your form or report is based. For example, suppose you have an Order Details form based on an Order Details table with a text box called ProductID that displays the ProductID field. To look up ProductName from a Products table based on the value in the text box, you could create another text box and set its ControlSource property to the following expression:

=DLookup("[ProductName]", "Products", "[ProductID] =" _ 
     & Forms![Order Details]!ProductID)

Tips

Although you can use the DLookup function to display a 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 then to base your form or report on that query.
You can also use the Lookup Wizard to find values in a foreign table.

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Example

The following example returns name information from the CompanyName field of the record satisfying criteria. The domain is a Shippers table. The criteria argument restricts the resulting set of records to those for which ShipperID equals 1.

Dim varX As Variant 
varX = DLookup("[CompanyName]", "Shippers", "[ShipperID] = 1")

The next example from the Shippers table uses the form control ShipperID to provide criteria for the DLookup function. Note that the reference to the control isn't included in the quotation marks that denote the strings. This ensures that each time the DLookup function is called, Microsoft Access will obtain the current value from the control.

Dim varX As Variant 
varX = DLookup("[CompanyName]", "Shippers", "[ShipperID] = " _ 
    & Forms!Shippers!ShipperID)

The next example uses a variable, intSearch, to get the value.

Dim intSearch As Integer 
Dim varX As Variant 
 
intSearch = 1 
varX = DLookup("[CompanyName]", "Shippers", _ 
    "[ShipperID] = " & intSearch)

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

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

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

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

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

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

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

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