How can join table with IN() in ON couse? - sql

Question

I have two table
User
id | name | category
1 | test | [2,4]
Category
id | name
1 | first
2 | second
3 | third
4 | fourth
now i need to join this both table and get data like:
name | category
test | second, fourth
i tried like:
select u.name as name, c.name as category
from user
INNER JOIN category on(c.id in (u.category))
but it's not working.

Answer 1

As others have suggested, if you have any control whatsoever over the design of this database, don't store multiple values in user.category, but instead have a bridging table between the two which maps one or more category values to each user record.
However, if you are not in a position to be able to redesign the database, here's a way to get the result you're looking for. First, let's create some test data:
create table [user]
(
id int,
[name] varchar(50),
category varchar(50) -- I'm assuming this is a string type
)
create table category
(
id int,
[name] varchar(50)
)
insert into [user] values
(1,'test','[2,4]'),
(2,'another test','[1,2,4]'),
(3,'more test','[1,3,2,4]')
insert into category values
(1,'first'),
(2,'second'),
(3,'third'),
(4,'fourth');
Then you can use a CTE with split_string to pull apart the individual category values, join them to their names, then recombine them into a single comma-separated value with for xml:
with r as
(
select
u.[name] as username,
cat.id,
cat.[name] as categoryname
from [user] u
outer apply
(
select value from string_split(substring(u.category,2,len(u.category)-2),',')
) c
left join category cat on c.value = cat.id
)
select
r.username,
stuff(
(select ',' + categoryname
from r r2
where r.username = r2.username
order by r2.id
for xml path ('')), 1, 1, '') as categories
from r
group by r.username
which gives the desired output:
/-----------------------------------------\
| username | categories |
|-------------|---------------------------|
|another test | first,second,fourth |
|more test | first,second,third,fourth |
|test | second,fourth |
\-----------------------------------------/
I'm making a couple of assumptions here:
You're using MS SQL Server
The category values always begin with [, end with ] and contain nothing but a comma-delimited string containing value category ids