Question

I have an Agent table and a hierarchy table.

CREATE TABLE [dbo].[Agent](
[AgentID] [int] IDENTITY(1,1) NOT NULL,
[FirstName] [varchar](50) NULL,
[LastName] [varchar](50) NULL,
CONSTRAINT [PK_Agent] PRIMARY KEY CLUSTERED 
(
    [AgentID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[Hierarchy](
    [HierarchyID] [int] IDENTITY(1,1) NOT NULL,
    [AgentID] [int] NULL,
    [NextAgentID] [int] NULL,
CONSTRAINT [PK_Hierarchy] PRIMARY KEY CLUSTERED 
(
    [HierarchyID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

–Insert to Agent

INSERT INTO [Agent]([FirstName],[LastName])VALUES('C1','C1');
INSERT INTO [Agent]([FirstName],[LastName])VALUES('C2','C2');
INSERT INTO [Agent]([FirstName],[LastName])VALUES('C3','C3');
INSERT INTO [Agent]([FirstName],[LastName])VALUES('C4','C4');

SELECT * FROM Agent;
AgentID FirstName   LastName
1       C1      C1
2       C2      C2
3       C3      C3
4       C4      C4

–Insert to Hierarchy

INSERT INTO [Hierarchy] ([AgentID],[NextAgentID]) VALUES (1,NULL);
INSERT INTO [Hierarchy] ([AgentID],[NextAgentID]) VALUES (2,1);
INSERT INTO [Hierarchy] ([AgentID],[NextAgentID]) VALUES (3,2);
INSERT INTO [Hierarchy] ([AgentID],[NextAgentID]) VALUES (2,4);
INSERT INTO [Hierarchy] ([AgentID],[NextAgentID]) VALUES (4,NULL);

SELECT * FROM Hierarchy;
HierarchyID AgentID NextAgentID
1       1   NULL
2       2   1
3       3   2
4       2   4
5       4   NULL

I used a common table expression to determine the bottom to top levels

WITH AgentHierarchy(AgentID, NextAgentID, HierarchyLevel)
AS
(
    SELECT
        H1.AgentID,
        H1.NextAgentID,
        1 HierarchyLevel
    FROM Hierarchy H1
    WHERE NOT EXISTS (SELECT 1 FROM Hierarchy H2 WHERE H2.NextAgentID = H1.AgentID)
    UNION ALL
    SELECT
        H.AgentID,
        H.NextAgentID,
        (AgentHierarchy.HierarchyLevel + 1) HierarchyLevel
    FROM Hierarchy H    
    INNER JOIN AgentHierarchy ON AgentHierarchy.NextAgentID = H.AgentID
)
SELECT DISTINCT
    AgentID,
    NextAgentID, 
    HierarchyLevel
FROM AgentHierarchy
ORDER BY AgentID, NextAgentID, HierarchyLevel;

Result is:

AgentID NextAgentID HierarchyLevel
1       NULL        3
2       1           2
3       2           1
4       NULL        1
2       4           1

My requirement is to show this in the below way:

AgentID NextAgentID HierarchyLevel
1       NULL        1
2       1           1
3       2           1
3       1           2
4       NULL        1
2       4           1
3       4           2

In short, recursively all the hierarchy with levels should be pulled with bottom-to-top approach. Please help me…

Answer 1

I found the answer:

WITH AgentHierarchy(AgentID, NextAgentID, HierarchyLevel)
AS
(
    SELECT
        H1.AgentID,
        H1.NextAgentID,
        1 HierarchyLevel
    FROM Hierarchy H1
    --WHERE NOT EXISTS (SELECT 1 FROM Hierarchy H2 WHERE H2.NextAgentID = H1.AgentID)
    UNION ALL
    SELECT
        AgentHierarchy.AgentID,
        H.NextAgentID,
        (AgentHierarchy.HierarchyLevel + 1) HierarchyLevel
    FROM Hierarchy H    
    INNER JOIN AgentHierarchy ON AgentHierarchy.NextAgentID = H.AgentID
)
SELECT 
    AgentHierarchy.AgentID,
    NextAgentID, 
    HierarchyLevel
FROM AgentHierarchy
WHERE NOT (NextAgentID IS NULL AND HierarchyLevel > 1);

I did the following changes:

1. Removed the Anchor query WHERE Clause.
2. Added the CTE’s AgentID in the second select after UNION.
3. Added WHERE Clause in the CTE to remove junk records for the
   bottom-most level with NULL NextAgentID.

Let me know if anyone has questions.