T-SQL loop through two tables - sql

Question

I have been unable to find a working solution for below dilemma.
I am using SQL Server 2016 and have the 2 tables shown below in a database.
Users table:
Id Name
----------
1 Lisa
2 Paul
3 John
4 Mike
5 Tom
Role table:
Id UserId Role
------------------------
1 3 Manager
2 2,4,5 Developer
3 1 Designer
I am looking for T-SQL code that loops through the Role table, extracts UserIds and retrieves associated name for each Id from the Users table.
So the looped result would look like this:
John
Paul,Mike,Tom
Lisa

Answer 1

FOR SQL SERVER 2017
SELECT R1.Id,STRING_AGG(U.Name , ','),R1.Role
FROM Users U
INNER JOIN
(
SELECT R.Id,S.value AS UserId,R.Role
FROM Role R
CROSS APPLY STRING_SPLIT (UserID, ',') S
) R1
ON U.Id=R1.UserId
GROUP BY R1.ID,R1.Role
ORDER BY R1.ID;
OR
FOR SQL SERVER 2016
WITH CTE AS
(
SELECT R2.ID,U.Name,R2.UserId,R2.Role
FROM Users U
INNER JOIN
(
SELECT R.Id,S.value AS UserId,R.Role
FROM Role R
CROSS APPLY STRING_SPLIT (UserID, ',') S
)R2
ON U.id=R2.UserId
)
SELECT DISTINCT R1.Id,
STUFF((
SELECT ',' + name
FROM CTE R3
WHERE R1.Role = R3.Role
FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)'), 1, 1, '') AS NAME
,R1.Role
FROM CTE AS R1;
OR
For Old versions
With CTE AS
(
SELECT r.id,
u.name,
r.Role
FROM Users u
INNER JOIN Role r
ON ',' + CAST(r.Userid AS NVARCHAR(20)) + ',' like '%,' + CAST(u.id AS NVARCHAR(20)) + ',%'
)
SELECT DISTINCT id,
STUFF((
SELECT ',' + name
FROM CTE md
WHERE T.Role = md.Role
FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)'), 1, 1, '') AS NAME,
Role
FROM
CTE AS T
ORDER BY id
Output
id NAME Role
1 John Manager
2 Paul,Mike,Tom Developer
3 Lisa Designer
Demo
http://sqlfiddle.com/#!18/04a2d/69

Answer 2

There are several problems going on here. The first issue is that you're storing your values in a delimited format. Next, because you're storing your values in a delimited format, the values are being stored as a varchar. This has problems as well, as, as I would guess that the value of your column Id in the table Users is an int; meaning an implicit cast is needed and ruining any SARGability.
So, the solution is to fix the problem, in my view. Because you have a many to many relationship, you'll need an extra table. Let's design the tables as you have them right now, anyway:
CREATE TABLE Users (Id int, Name varchar(100));
CREATE TABLE Role (Id int, UserId varchar(100), [Role] varchar(100));
INSERT INTO Users
VALUES (1,'Lisa'),
(2,'Paul'),
(3,'John'),
(4,'Mike'),
(5,'Tom');
INSERT INTO Roles
VALUES(1,'3','Manager'),
(2,'2,4,5','Developer'),
(3,'1','Designer');
Now, instead we need a new table:
CREATE TABLE UserRoles (Id int, UserID int, RoleID int);
Now, we can insert the proper rows into the database. As you're using SQL Server 2016, we can use STRING_SPLIT:
INSERT INTO UserRoles (UserID, RoleID)
SELECT SS.value, R.Id
FROM Roles R
CROSS APPLY STRING_SPLIT (UserID, ',') SS;
After this, if you want, you could drop your existing column using the following, however, I see no harm in leaving it at the moment:
ALTER TABLE Roles DROP COLUMN UserID;
Now, we can query the data correctly:
SELECT *
FROM Users U
JOIN UserRoles UR ON U.ID = UR.UserID
JOIN Roles R ON UR.RoleID = R.Id;
If you want to then delimit this data, you can use STUFF, but don't store it back; I've explained how to correct your data for a reason! :)
SELECT [Role],
STUFF((SELECT ',' + [Name]
FROM Users U
JOIN UserRoles UR ON U.Id = UR.UserID
WHERE UR.RoleID = R.Id
FOR XML PATH ('')),1,1,'') AS Users
FROM Roles R;
If you were using SQL Server 2017, you'd be able to use STRING_AGG
Clean up script:
DROP TABLE UserRoles;
DROP TABLE Users;
DROP TABLE Roles;

Answer 3

Try this solution:
declare #users table (Id int, Name varchar(100))
declare #role table (Id int, UserId varchar(100), [Role] varchar(100))
insert into #users values
(1, 'Lisa'),
(2, 'Paul'),
(3, 'John'),
(4, 'Mike'),
(5, 'Tom')
insert into #role values
(1, '3', 'Manager'),
(2, '2,4,5', 'Developer'),
(3, '1', 'Designer')
select * from #role [r]
join #users [u] on
CHARINDEX(',' + cast([u].Id as varchar(3)) + ',', ',' + [r].UserId + ',', 1) > 0
I joined both tables based on occurence Id in UserId. To make it possible and avoid matches like: 2 is matched to 12, I decided to match only IDs surrounded by commas. That's why I wrapped in commas Id in a query and also wrapped UserId in commas, to match IDs at the end and the beginning of userId.
This query should give you satisfying result, but to match your desired output exatcly, you have to wrap this query in a CTE and perform group by with string concatenation:
;with cte as (
select [r].Id, [r].Role, [u].Name from #role [r]
join #users [u] on
CHARINDEX(',' + cast([u].Id as varchar(3)) + ',', ',' + [r].UserId + ',', 1) > 0
)
select Id,
(select Name + ',' from cte where Id = [c].Id for xml path('')) [Name],
--I believe this should work in your case, if so, just pick one column from these two
string_agg(Name + ',') [Name2],
Role
from cte [c]
group by Id, Role