一张桌子上的MySQL动态交叉表数据透视表比较

Question

I have a many to many table setup. This is an example of table I am focusing on.

many_to_many_id, foreign_key_id
1, 1
1, 2
1, 3
2, 1
2, 2
3, 1
3, 4

I need to given many_to_many_id 1 find any other many_to_many_ids that have matching foreign keys that exist within the first set. Given the first set 1, 2, 3 attached to many_to_many_id would return 2 as 1, and 2 are inside the set, but 3 would not be returned as 4 is not part of the test set. My boss has said I should use a dynamic cross tab to create two tables to compare with a join. I have looked for examples but they have not been helpful.

Answer 1

You can do this with a few simple sub-queries. The first will make sure that for each many_to_many_id there is at least one foreign_key_id in the set you're looking for (1, 2, 3) and the second will make sure there isn't even one foreign_key_id not in the set you're looking for.

SET @search_id = 1;

SELECT m.many_to_many_id FROM SampleTable m
WHERE m.many_to_many_id != @search_id
AND     EXISTS ( SELECT 1 FROM SampleTable a WHERE a.many_to_many_id = m.many_to_many_id AND a.foreign_key_id IN ( SELECT b.foreign_key_id FROM SampleTable b WHERE b.many_to_many_id = @search_id ) )
AND NOT EXISTS ( SELECT 1 FROM SampleTable a WHERE a.many_to_many_id = m.many_to_many_id AND a.foreign_key_id NOT IN ( SELECT b.foreign_key_id FROM SampleTable b WHERE b.many_to_many_id = @search_id ) )
GROUP BY m.many_to_many_id

SQL Fiddle Here