How to count values conditionally in SQL

Question

I have an index table of entity attribute values that looks like this: +-----------+--------------+----------+-------+ | entity_id | attribute_id | store_id | value | +-----------+--------------+----------+-------+ | 38 | 190 | 1 | 22 | | 38 | 190 | 1 | 23 | | 39 | 190 | 1 | 22 | | 39 | 190 | 1 | 23 | | 39 | 190 | 1 | 42 | | 40 | 190 | 1 | 22 | | 41 | 190 | 1 | 54 | | 42 | 190 | 1 | 54 | | 43 | 190 | 1 | 22 | | 44 | 190 | 1 | 22 | | 45 | 190 | 1 | 54 | +-----------+--------------+----------+-------+

As you can see, a single entity can have multiple values for a single attribute (entity_id 38 has values 22,23) and these values are not unique per entity (entity_id 38,39 both share value 22).

The first problem to solve is getting the number of distinct entities per value; this is easily accomplished with:

SELECT value, COUNT(entity_id) AS count
FROM catalog_product_index_eav
WHERE attribute_id=190
GROUP BY value;

which results in: +-------+-------+ | value | count | +-------+-------+ | 22 | 5 | | 23 | 2 | | 42 | 1 | | 54 | 3 | +-------+-------+

My question is how can I nest an OR condition in this count, namely: for some specific value Y, for each value X, count the number of entities that have either value X or Y.

I would like to do this in a single query. For instance, for attribute_id 190 and value 23, the output from above example should be: +-------+-------+ | value | count | +-------+-------+ | 22 | 5 | # all entities with value 22 happen to have 23 as well | 23 | 2 | that is, one is a subset of the other | 42 | 2 | # intersection is nonempty | 54 | 5 | # sets are disjoint +-------+-------+

Answer 1

select c1.value, 
( SELECT COUNT(DISTINCT entity_id) as count 
  FROM catalog_product_index_eav 
  where attribute_id=81 
  and (value=c1.value || value=7) ) as count 
FROM catalog_product_index_eav c1 
WHERE attribute_id=81 
GROUP BY c1.value