如何从具有匹配列的两个不同 SELECT 语句中获取行

Question

I have a table called relationships in my MySQL database which has the columns follower_id and followed_id. These represent followings on Instagram, for example if an account with ID 1 followed an account with ID 2 then a row would exist in my table where follower_id was 1 and followed_id was 2.

What I want to do is be able to find accounts that follow both account with ID 1 AND account with ID 4 for example. I have tried creating temporary tables using SELECT statements like this:

CREATE TEMPORARY TABLE temp1 
SELECT follower_id FROM relationships 
WHERE followed_id = '1'

and

CREATE TEMPORARY TABLE temp2 
SELECT follower_id FROM relationships 
WHERE followed_id = '4'

and trying to cross reference the two temporary tables but this takes a very long time. Is there a quicker way to do this in MySQL?

Answer 1

Simply you can select distinct follower_id using below query:-

SELECT DISTINCT follower_id FROM relationships 
WHERE followed_id IN ('1', '4');

Hope, this will solve your problem.

Answer 2

SELECT follower_id FROM relationships WHERE followed_id=1 AND follower_id IN 
(SELECT follower_id FROM relationships WHERE followed_id=4)

Answer 3

A pretty simple method is:

SELECT follower_id
FROM relationships 
WHERE followed_id IN (1, 4)
GROUP BY follower_id
HAVING COUNT(*) = 2;  -- number of followed