如果另一列包含所有请求值集，如何从表中选择特定列？

Question

I have a table in MySQL named table1 which has three columns id , user_id (foreign_key) and destination_id (foreign_key). One user can have multiple destinations.

E.g Table1

id      user_id       destination_id
1         10            2
2          5            3
3         10            4
4         10            5
5          9            10
6          5            12
7          8            2 

I get a request from the client side in PHP script; the request includes destination ids in an array.

E.g. $request = array('destination_id' => [2,4,5]);

I just want to get all the user_id from table1 if and only if the particular user_id contains all requested destinations.

I tried to achieve this using 'IN' operator. ie

     SELECT user_id FROM table1 WHERE destination_id IN ($requestedDestinationsInCommaSeparatedString)

It gives row including user_id 8 along with user_id 10 but I just need user_id 10. I just wanted to know the concept regarding the solution to the following problem. I am a beginner in SQL, any help would be very appreciable. Thanks.

Answer 1

You can check that a user_id refers to all requested destination by grouping and counting the destinations.

SELECT user_id
FROM table1 
WHERE
    destination_id IN (2,4,5)
GROUP BY
    user_id
HAVING count(*) = 3
-- count must be the number of elments in (2,4,5)

For doing so, the field combination of user_id and destination_id must be unique over all records.

Answer 2

The only thing I can think of is to use multiple subselects and build the query string in PHP.

So for your specific example the SQL-Query-String generated should be

SELECT user_id
FROM table1 

WHERE user_id IN
    (SELECT user_id FROM table1 WHERE destination_id = 2)
AND user_id IN
    (SELECT user_id FROM table1 WHERE destination_id = 4)
AND user_id IN
    (SELECT user_id FROM table1 WHERE destination_id = 5)

GROUP BY user_id

I think programming the function which generates the middle part for you shouldn't be too hard.