Populating a Table with Existing Hierarchical Data

This task creates a new table and populates it with the data in the EmployeeDemo table. This task has the following steps:

• Create a new table that contains a hierarchyid column. This column could replace the existing EmployeeID and ManagerID columns. However, you will retain those columns. This is because existing applications might refer to those columns, and also to help you understand the data after the transfer. The table definition specifies that OrgNode is the primary key, which requires the column to contain unique values. The clustered index on the OrgNode column will store the date in OrgNode sequence.

• Create a temporary table that is used to track how many employees report directly to each manager.

• Populate the new table by using data from the EmployeeDemo table.

To create a new table named NewOrg

• In a Query Editor window, run the following code to create a new table named HumanResources.NewOrg:

  CREATE TABLE NewOrg
  (
    OrgNode hierarchyid,
    EmployeeID int,
    LoginID nvarchar(50),
    ManagerID int
  CONSTRAINT PK_NewOrg_OrgNode
    PRIMARY KEY CLUSTERED (OrgNode)
  );
  GO
  

To create a temporary table named #Children

1. Create a temporary table named #Children with a column named Num that will contain the number of children for each node:

   CREATE TABLE #Children 
      (
       EmployeeID int,
       ManagerID int,
       Num int
   );
   GO
   

2. Add an index that will significantly speed up the query that populates the NewOrg table:

   CREATE CLUSTERED INDEX tmpind ON #Children(ManagerID, EmployeeID);
   GO
   

To populate the NewOrg table

1. Recursive queries forbid subqueries with aggregates. Instead, populate the #Children table with the following code, which uses the ROW_NUMBER() method to populate the Num column:

   INSERT #Children (EmployeeID, ManagerID, Num)
   SELECT EmployeeID, ManagerID,
     ROW_NUMBER() OVER (PARTITION BY ManagerID ORDER BY ManagerID) 
   FROM EmployeeDemo
   GO
   

2. Review the #Children table. Note how the Num column contains sequential numbers for each manager.

   SELECT * FROM #Children ORDER BY ManagerID, Num
   GO
   

   Here is the result set.

   EmployeeID ManagerID Num

   ---------- --------- ---

   1 NULL 1

   2 1 1

   3 1 2

   4 2 1

   5 2 2

   6 2 3

   7 3 1

   8 3 2

   9 4 1

   10 4 2

3. Populate the NewOrg table. Use the GetRoot and ToString methods to concatenate the Num values into the hierarchyid format, and then update the OrgNode column with the resultant hierarchical values:

   WITH paths(path, EmployeeID) 
   AS (
   -- This section provides the value for the root of the hierarchy
   SELECT hierarchyid::GetRoot() AS OrgNode, EmployeeID 
   FROM #Children AS C 
   WHERE ManagerID IS NULL 
   
   UNION ALL 
   -- This section provides values for all nodes except the root
   SELECT 
   CAST(p.path.ToString() + CAST(C.Num AS varchar(30)) + '/' AS hierarchyid), 
   C.EmployeeID
   FROM #Children AS C 
   JOIN paths AS p 
      ON C.ManagerID = P.EmployeeID 
   )
   INSERT NewOrg (OrgNode, O.EmployeeID, O.LoginID, O.ManagerID)
   SELECT P.path, O.EmployeeID, O.LoginID, O.ManagerID
   FROM EmployeeDemo AS O 
   JOIN Paths AS P 
      ON O.EmployeeID = P.EmployeeID
   GO
   

4. A hierarchyid column is more understandable when you convert it to character format. Review the data in the NewOrg table by executing the following code, which contains two representations of the OrgNode column:

   SELECT OrgNode.ToString() AS LogicalNode, * 
   FROM NewOrg 
   ORDER BY LogicalNode;
   GO
   

   The LogicalNode column converts the hierarchyid column into a more readable text form that represents the hierarchy. In the remaining tasks, you will use the ToString() method to show the logical format of the hierarchyid columns.

5. Drop the temporary table, which is no longer needed:

   DROP TABLE #Children
   GO
   

The next task will create indexes to support the hierarchical structure.

Next Task in Lesson

Optimizing the NewOrg Table