如果左联接为IS AND IS NOT（MYSQL），则为SELECT？

Question

I got one table "people".

Another one with "hobbiesConnection", and they are connected as an OneToMany.

I would like to build a search, where it is possible to search people which have a hobby and don't have a hobby.

Something like :

SELECT * FROM people
LEFT JOIN hobbiesConnection ON hobbiesConnection.people_id = 
hobbiesConnection.hobby_id
WHERE hobby_id = 4 AND hobby_id != 5

Now I get the person with the hobby 4, but I want to get an empty result, because both conditions have to fit to the person.

Does anybody have an idea how to accomplish this ?

Answer 1

Firstly, your JOIN is not correct. The two tables should be linked with a foreign key / common column. Try the below query;

SELECT * FROM people
LEFT JOIN hobbiesConnection 
ON hobbiesConnection.people_id = people.people_id
And (hobbiesConnection.hobby_id = 4 AND hobbiesConnection.hobby_id != 5)

Answer 2

use (NOT) EXISTS clause:

SELECT * FROM people p
WHERE TRUE
AND EXISTS (
  SELECT TRUE FROM hobbiesConnection hc 
  WHERE hc.people_id = p.people_id -- or p.id? you didnt mention
  AND hobby_id = 4
)
AND NOT EXISTS (
  SELECT TRUE FROM hobbiesConnection hc 
  WHERE hc.people_id = p.people_id -- or p.id? you didnt mention
  AND hobby_id = 5
)

You can achieve the same using joins

SELECT p.* 
FROM people p
JOIN hobbiesConnection h4 ON TRUE
    AND h4.people_id = p.people_id -- or p.id? you didnt mention
    AND h4.hobby_id = 4
LEFT JOIN hobbiesConnection h5 ON TRUE
    AND h5.people_id = p.people_id -- or p.id? you didnt mention
    AND h5.hobby_id = 5
WHERE h5.id IS NULL -- or whatever column from that table

have a look at the fiddle: http://sqlfiddle.com/#!9/d9926/4