Index.DistinctCount property (DAO)

Applies to: Access 2013, Office 2013

Returns a value that indicates the number of unique values for the Index object that are included in the associated table (Microsoft Access workspaces only).

Syntax

expression .DistinctCount

expression A variable that represents an Index object.

Remarks

Check the DistinctCount property to determine the number of unique values, or keys, in an index. Any key is counted only once, even though there may be multiple occurrences of that value if the index permits duplicate values. This information is useful in applications that attempt to optimize data access by evaluating index information. The number of unique values is also known as the cardinality of an Index object.

The DistinctCount property won't always reflect the actual number of keys at a particular time. For example, a change caused by a rolled back transaction won't be reflected immediately in the DistinctCount property. The DistinctCount property value also may not reflect the deletion of records with unique keys. The number will be accurate immediately after you use the CreateIndex method.

Example

This example uses the DistinctCount property to show how you can determine the number of unique values in an Index object. However, this value is only accurate immediately after creating the Index. It will remain accurate if no keys change, or if new keys are added and no old keys are deleted; otherwise, it will not be reliable. (If this procedure is run several times, you can see the effect on the DistinctCount property values of the existing Index objects.)

    Sub DistinctCountX() 
     
     Dim dbsNorthwind As Database 
     Dim tdfEmployees As TableDef 
     Dim idxCountry As Index 
     Dim idxLoop As Index 
     Dim rstEmployees As Recordset 
     
     Set dbsNorthwind = OpenDatabase("Northwind.mdb") 
     Set tdfEmployees = dbsNorthwind!Employees 
     
     With tdfEmployees 
     ' Create and append new Index object to the Employees 
     ' table. 
     Set idxCountry = .CreateIndex("CountryIndex") 
     idxCountry.Fields.Append _ 
     idxCountry.CreateField("Country") 
     .Indexes.Append idxCountry 
     
     ' The collection must be refreshed for the new 
     ' DistinctCount data to be available. 
     .Indexes.Refresh 
     
     ' Enumerate Indexes collection to show the current 
     ' DistinctCount values. 
     Debug.Print "Indexes before adding new record" 
     For Each idxLoop In .Indexes 
     Debug.Print " DistinctCount = " & _ 
     idxLoop.DistinctCount & ", Name = " & _ 
     idxLoop.Name 
     Next idxLoop 
     
     Set rstEmployees = _ 
     dbsNorthwind.OpenRecordset("Employees") 
     
     ' Add a new record to the Employees table. 
     With rstEmployees 
     .AddNew 
     !FirstName = "April" 
     !LastName = "LaMonte" 
     !Country = "Canada" 
     .Update 
     End With 
     
     ' Enumerate Indexes collection to show the modified 
     ' DistinctCount values. 
     Debug.Print "Indexes after adding new record and " & _ 
     "refreshing Indexes" 
     .Indexes.Refresh 
     For Each idxLoop In .Indexes 
     Debug.Print " DistinctCount = " & _ 
     idxLoop.DistinctCount & ", Name = " & _ 
     idxLoop.Name 
     Next idxLoop 
     
     ' Delete new record because this is a demonstration. 
     With rstEmployees 
     .Bookmark = .LastModified 
     .Delete 
     .Close 
     End With 
     
     ' Delete new Indexes because this is a demonstration. 
     .Indexes.Delete idxCountry.Name 
     End With 
     
     dbsNorthwind.Close 
     
    End Sub