TSQL to recurse based on a condition - sql

Question

I have a query to get list of members in a group as below
;WITH CTE (GroupName, GroupMember, isMemberGroup)
AS (SELECT ag.name,
agm.Member,
agm.MemberIsGroup
FROM tb1 ag
LEFT JOIN tb2 agm
ON ag.ID = agm.ID
WHERE ag.name = 'somegroupame')
SELECT *
FROM CTE
Group Name Group Member IsMemberGroup
Admin John 0
Admin Sam 0
Admin GDBA 1
xyz Dan 0
xyz GXy 1
I want to write a query to get members of the sub group as well if IsMemberGroup is 1. Please guide me how to achieve that.
The expected result is to get a list of members including members of sub groups for a give group. The recursion should happen for all the sub groups' groups as well if any:
Resultant: Admin
Group Group Member
Admin John
Admin Sam
Admin(GDBA) Mike
Admin(GDBA) June
Admin(GDBA/Bcksdmin)Mark

Answer 1

You could solve this problem using a recursive CTE to generate your group member hierarchy.
This example using the following data:
/* Let's create some sample data to experiment with.
*/
DECLARE #Sample TABLE
(
GroupName VARCHAR(50),
GroupMember VARCHAR(50),
IsMemberGroup BIT
)
;
INSERT INTO #Sample
(
GroupName,
GroupMember,
IsMemberGroup
)
VALUES
('Admin', 'John', 0),
('Admin', 'Sam', 0),
('Admin', 'GDBA', 1),
('GDBA', 'Mike', 0),
('GDBA', 'June', 0),
('GDBA', 'Bcksdmin', 1),
('Bcksdmin', 'Mark', 0)
;
The query uses the CTE to calculate the group hierarchy. This is then joined back to the original data, like so:
/* Using a recursive CTE we can build the group name
* hierarchy.
*/
WITH [Group] AS
(
/* Anchor query returns all top level teams, ie
* those that do not appear in the group member
* field.
*/
SELECT
s1.GroupName,
CAST(s1.GroupName AS VARCHAR(MAX)) AS Breadcrumb
FROM
#Sample AS s1
LEFT OUTER JOIN #Sample AS s2 ON s2.GroupMember = s1.GroupName
WHERE
s2.GroupName IS NULL
GROUP BY
s1.GroupName
UNION ALL
/* Using recursion, find all children.
* (Sub groups are identified by the IsMemberGroup flag).
*/
SELECT
s.GroupMember AS GroupName,
g.Breadcrumb + '/' + s.GroupMember
FROM
[Group] AS g
INNER JOIN #Sample AS s ON s.GroupName = g.GroupName
WHERE
s.IsMemberGroup = 1
)
SELECT
g.Breadcrumb,
s.GroupMember
FROM
#Sample AS s
INNER JOIN [Group] AS g ON g.GroupName = s.GroupName
WHERE
s.IsMemberGroup = 0
;
Although this solution works I would suggest you revisit the table design, if possible. The column GroupMember is pulling double duty by storing both teams and team members. Splitting this into Group (with parent lookup column) and GroupMember tables would simplify the task. Each new table would only need to describe one real world object, making it clearer where new columns should be created.