Does anyone know of an elegant way to determine, within a query, whether
two arbitrary lists have common element?
I am quite fond of queries using "in", e.g: select * from A where 23 in
(A.list) - where A.list is a comma-separated list of numbers in a
varchar(255) field.
Now I need something like: select * from A where (23,43,21,52,74) in
(A.list) to work - but it doesn't.
(23,42,21,52,74) is a list of credentials that the current user has.
(A.list) is the list of acceptable credentials to access the record. I
just need to detect a common element.
And I can find no other way to do it other than breaking my user credential
list into several tests, like:
select * from A where (23 in (A.list)) or (42 in (A.list)) or (21 in
(A.list)), etc.
That's what I'm doing now. But it's not pretty and can generate some
rather long query strings. Another alternative would be to do a three way
join on a user credential table, access control table, and the table A.
But that seems wasteful too.
I suppose what I'm looking for is the equivolent of an "intersection"
operation between two sets. But I can't use MySql sets because they are
bit fields that allow only 64 members. Does anyone know a more efficient
or elegant way to do this with MySQL?
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