Showing posts with label Display Hierarchy. Show all posts
Showing posts with label Display Hierarchy. Show all posts

August 14, 2015

SQL Server: Use of Recursive Query with example

One of the most benefit of CTE (Common Table Expressions) is that we can create recursive queries with them.
Recursive query is the efficient way to display hierarchy setup (Parent child relation ship in the same table). e.g. Grand Parent, Parent, Child. This is common requirement. To display the parent child relationship in efficient manner, we can use Recursive CTE. Let me explain it by example.
Create Temporary Table:
 [ResourceID] [int] NOT NULL,
 [ChildOf] [int] NOT NULL,
 [ResourceName] [varchar](250) NOT NULL
Lets populate some data into this table:
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (5, 0, N'Mammal')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (6, 5, N'Carnivore')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (14, 6, N'Cannine')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (15, 14, N'Dog')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (16, 15, N'Dog1')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (17, 14, N'Monkey')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (18, 17, N'Monkey1')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (19, 16, N'dog1.01')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (21, 18, N'monkey1.02')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (23, 17, N'test')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (25, 17, N'Monkey 2')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (31, 0, N'Fish')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (32, 31, N'cartilaginous fish')
INSERT @Images ([ResourceID], [ChildOf], [ResourceName]) VALUES (33, 32, N'dogfish')
That is how data is stored in the table:
This is not the way that we can understand the hierarchy. Recursive query will help us to display result like this:
This is much efficient way to list out, as we understand that how the hierarchy is being maintained. Recursive CTE helps us to generate this kind efficient output. Let me share the t-sql script which generates the output which we are looking for:
;WITH images
AS (
   ORDER BY ResourceID
   ) AS RowID
 FROM @images
AS (
 SELECT 1 AS [Level]
  ,cast(cast(RowID AS VARBINARY(4)) AS VARBINARY(max)) AS sort
 FROM images
 WHERE ChildOf = 0
 --where [ResourceID] = 5
 SELECT p.[Level] + 1
  ,cast(p.sort + cast(c.RowID AS VARBINARY(4)) AS VARBINARY(max))
 FROM images c
 INNER JOIN cte p ON p.[ResourceID] = c.ChildOf
  --WHERE c.ChildOF=5
 ,REPLICATE('.', ([Level] - 1) * 4) + [ResourceName] AS menu
FROM cte
That's it. Here, I have used first CTE, to assign the Unique numbers. Then just iterate thru each record and find their related children records. Hope this helps you.
Reference : Tejas Shah