Question

Work on SQL-Server. My table structure is below

CREATE TABLE [dbo].[AgentInfo](
    [AgentID] [int] NOT NULL,
    [ParentID] [int] NULL,
 CONSTRAINT [PK_AgentInfo] 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
INSERT [dbo].[AgentInfo] ([AgentID], [ParentID]) VALUES (1, -1)
INSERT [dbo].[AgentInfo] ([AgentID], [ParentID]) VALUES (2, -1)
INSERT [dbo].[AgentInfo] ([AgentID], [ParentID]) VALUES (3, 1)
INSERT [dbo].[AgentInfo] ([AgentID], [ParentID]) VALUES (4, 2)

Required output

Use my below syntax get required output but not satisfied. Is there any better way to get the required output

--get parent child list
---step--1 
SELECT * 
INTO #temp1 
FROM  ( SELECT a.AgentID ,
            a.ParentID,
            a.AgentID AS BaseAgent
        FROM dbo.AgentInfo a WHERE ParentID=-1
        UNION ALL         
        SELECT   a.ParentID  ,
            0 as AgentID,
            a.AgentID AS BaseAgent 
        FROM dbo.AgentInfo a WHERE ParentID!=-1
        UNION ALL
        SELECT   a.AgentID  ,
            a.ParentID,
            a.AgentID AS BaseAgent 
        FROM dbo.AgentInfo a 
        WHERE ParentID!=-1 
     ) AS d

SELECT * FROM #temp1
DROP TABLE #temp1

Help me to improve my syntax. If you have any questions please ask.

Answer 1

You could use a recursive SELECT, see the examples in the documentation for WITH, starting with example D.

The general idea within the recursive WITH is: You have a first select that is the starting point, and then a UNION ALL and a second SELECT which describes the step from on level to the next, where the previous level can either be the result of the first select or the result of the previous run of the second SELECT.