SELECT entity_id
FROM entities
WHERE part1='Foo'
OR part2='Foo'
OR part3='Foo'
...
OR part12='Foo';

##</code><code>##

SELECT entity_id
FROM entities
WHERE 'Foo' IN (part1, part2, part3, ..., part12);

##</code><code>##

SELECT e.entity_id
FROM entities e
INNER JOIN entity_parts ep ON e.entity_id=ep.entity_id
WHERE ep.part='Foo'

##</code><code>##

SELECT e.entity_id
FROM entities e
INNER JOIN entity_parts ep1 ON e.entity_id=ep1.entity_id
INNER JOIN entity_parts ep2 ON e.entity_id=ep2.entity_id
WHERE ep1.part='Foo'
AND ep2.part IN ('Bar', 'Baz')