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)') + '%'

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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.

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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).