Compare two list items - sql

Question

I am trying to compare a database field which stores list items (comma separated) with unfortunately a variable which is also a list item.
Example:
In this case, a user can belong to multiple groups, and content access is also allocated to multiple groups.
contentid | group
(1) (c,d)
(2) (a,c)
(3) (b)
So, I need to select all content where user is in group (a,c). In this case, contentid 1,2 should be returned.

Answer 1

Here's a safe but slow solution for SQL 2008
BEGIN
-- setup
DECLARE #tbl TABLE (
[contentid] INT
,[group] VARCHAR(MAX)
)
INSERT INTO #tbl VALUES
(1, 'c,d')
,(2, 'a,c')
,(3, 'd')
-- send your request as simple xml
DECLARE #param XML
SET #param = '<g>a</g><g>c</g>'
-- query
SELECT DISTINCT contentid
FROM #tbl t
INNER JOIN #param.nodes('/g') AS t2(g)
ON ',' + t.[group] + ',' LIKE '%,' + t2.g.value('.', 'varchar(max)') + ',%'
END
You just pass your query in as an XML snippet instead of a comma separated list.
If your group names are single characters or you can be sure the names are not character-subsets of each other (ie: GroupA, GroupAB), then the query can be optimized to.
ON t.[group] LIKE '%' + t2.g.value('.', 'varchar(max)') + '%'
If you're using a RDBMS without XML parsing capability you'll have to use string split your query into a temp table and work it that way.
You really should not be using comma separated values inside your columns. It would be much better if the [group] column only contained one value and you had repeated entries with a UNIQUE constraint on the composite (contentid, group).

Answer 2

You might find this question and answer useful : How do I split a string so I can access item x?
Or you could always use something like this :
create function SplitString(
#string varchar(max),
#delimiter char(1)
)
returns #items table (item varchar(max))
as
begin
declare #index int set #index = 0
if (#delimiter is null) set #delimiter = ','
declare #prevdelimiter int set #prevdelimiter = 0
while (#index < len(#string)) begin
if (substring(#string, #index, 1) = #delimiter) begin
insert into #items
select substring(#string, #prevdelimiter, #index-#prevdelimiter)
set #prevdelimiter = #index + 1
end
set #index = #index + 1
end
--last item (or only if there were no delimiters)
insert into #items
select substring(#string, #prevdelimiter, #index - #prevdelimiter + 1)
return
end
go
declare #content table(contentid int, [group] varchar(max))
insert into #content
select 1, 'c,d'
union
select 2, 'a,c'
union
select 3, 'b'
declare #groups varchar(max) set #groups = 'a,c'
declare #grouptable table(item varchar(max))
insert into #grouptable
select * from dbo.SplitString(#groups, ',')
select * From #content
where (select count(*) from #grouptable g1 join dbo.SplitString([group], ',') g2 on g1.item = g2.item) > 0