Access SQL 不支持递归(如 SQL Server 中的递归 CTE),但以下 VBA 代码将采用名为 [Employees] 的输入表...
ID EmployeeName ReportsTo
-- ------------ ---------
1 Jane
2 Joe 1
3 John 2
4 Julia 2
5 Jack 4
6 Jimbo 2
7 Jill 5
...并填充一个名为 [EmployeeHierarchy] 的表...
Superior Subordinate LevelDifference
-------- ----------- ---------------
Jane Joe 1
Joe John 1
Jane John 2
Joe Julia 1
Jane Julia 2
Julia Jack 1
Joe Jack 2
Jane Jack 3
Jack Jill 1
Julia Jill 2
Joe Jill 3
Jane Jill 4
Joe Jimbo 1
Jane Jimbo 2
...像这样:
Option Compare Database
Option Explicit
Sub OrgTree()
Dim cdb As DAO.Database, rstTop As DAO.Recordset
Set cdb = CurrentDb
cdb.Execute "DELETE FROM EmployeeHierarchy", dbFailOnError
Set rstTop = cdb.OpenRecordset( _
"SELECT ID, EmployeeName " & _
"FROM Employees " & _
"WHERE ReportsTo IS NULL", _
dbOpenSnapshot)
' process each top-level entity
Do While Not rstTop.EOF
ProcessSubordinates rstTop!ID, rstTop!EmployeeName, 0
rstTop.MoveNext
Loop
rstTop.Close
Set rstTop = Nothing
Set cdb = Nothing
End Sub
Sub ProcessSubordinates(BaseID As Long, BaseName As String, RecursionLevel As Long)
Dim rstSubs As DAO.Recordset
Dim i As Long, CurrentID As Long, SuperiorID As Long, SuperiorName As String
Set rstSubs = CurrentDb.OpenRecordset( _
"SELECT ID, EmployeeName " & _
"FROM Employees " & _
"WHERE ReportsTo = " & BaseID, _
dbOpenSnapshot)
' loop through immediate subordinates for the "base" employee
Do While Not rstSubs.EOF
AddToEmployeeHierarchy BaseName, rstSubs!EmployeeName, 1
' traverse back up the tree to list all other superiors
CurrentID = BaseID
For i = 1 To RecursionLevel
SuperiorID = DLookup("ReportsTo", "Employees", "ID = " & CurrentID)
SuperiorName = DLookup("EmployeeName", "Employees", "ID = " & SuperiorID)
AddToEmployeeHierarchy SuperiorName, rstSubs!EmployeeName, i + 1
CurrentID = SuperiorID
Next
' and recurse to process down the tree for the current subordinate
ProcessSubordinates rstSubs!ID, rstSubs!EmployeeName, RecursionLevel + 1
rstSubs.MoveNext
Loop
rstSubs.Close
Set rstSubs = Nothing
End Sub
Sub AddToEmployeeHierarchy(SuperiorName As String, SubordinateName As String, LevelDifference As Long)
Dim rst As DAO.Recordset
Set rst = CurrentDb.OpenRecordset("EmployeeHierarchy", dbOpenTable)
rst.AddNew
rst!Superior = SuperiorName
rst!Subordinate = SubordinateName
rst!LevelDifference = LevelDifference
rst.Update
rst.Close
Set rst = Nothing
End Sub