Lookup from a comma separated SQL column - sql

Question

I have a user table which has comma separated ids in one of the columns, like:
Id
Name
PrimaryTeamId
SecondaryTeamIds
1
John
123
456,789,669
2
Ringo
123
456,555
and a secondary table which contains the team names
Id
TeamId
TeamName
1
456
Red Team
2
669
Blue Team
3
789
Purple Team
4
555
Black Team
5
123
Orange Team
I'm trying to create a view which gives the following format:
Name
Primary Team
Secondary Teams
John
Orange Team
Red Team, Purple Team, Blue Team
Ringo
Orange Team
Red Team, Black Team
I have created
select
u.Name,
t.TeamName as 'Primary Team'
SELECT ... ?? as 'Secondary Teams'
from
users u
inner join teams t on u.PrimaryTeamId = t.TeamId
I've tried numerous things but can't seem to put it together. I can't seem to find the same use case here or elsewhere. I do control the data coming in so I could parse those values out relationally to begin with or do some kind of lookup on the ETL side, but would like to figure it out.

Answer 1

If the sequence of Secondary Teams is essential, you can parse the string via OpenJSON while preserving the sequence [key].
Then it becomes a small matter of string_agg()
Example or dbFiddle
Select A.ID
,A.Name
,PrimaryTeam = C.TeamName
,B.SecendaryTeams
from YourTable A
Cross Apply (
Select SecendaryTeams = string_agg(B2.TeamName,', ') within group (order by B1.[Key])
From OpenJSON( '["'+replace(string_escape([SecondaryTeamIds],'json'),',','","')+'"]' ) B1
Join YourTeams B2 on B1.Value=B2.TeamID
) B
Join YourTeams C on A.[PrimaryTeamId]=C.TeamId
Results
ID Name PrimaryTeam SecendaryTeams
1 John Orange Team Red Team, Purple Team, Blue Team
2 Ringo Orange Team Red Team, Black Team

Answer 2

I played around with this a little bit and I found you can do it using two functions, STRING_SPLIT and STRING_AGG.
STRING_SPLIT allows you to convert a NVARCHAR and split it into a table where each row is a value, and STRING_AGG allows you to do the opposite, Join a table into a NVARCHAR. Then I just used a JOIN in between.
Maybe its not the cleanest solution but it does the job. Also its a bit inefitient but using native functions instead of loops help a lot.
I attach a working example. In this online editor I just had one table so I joined it with itself but it must work joining with other tables.
SELECT
*,
(
SELECT STRING_AGG(CAST(Val AS NVARCHAR), ', ') -- concatenates the rows together
FROM
(
SELECT demo.hint AS Val
FROM STRING_SPLIT((SELECT d.name FROM demo as d where id = demo.id), ',') -- splits the row by comas
JOIN demo ON value = demo.id -- joins so that the values are replaced with names
) Vals
) as JointValues -- name of the column with the joint values
FROM demo