I'm defining the relationship between the two tables using a join table. I want to arrange them in the order of many overlapping things. Currently, we are using subquery, is there a way to get the same result using join?
People FoodTable PeopleFood
ID | NAME ID | Food ID | PeopleId | FoodId
1 BOB 1 Hamberger 1 1 1
2 JOHN 2 Pizza 2 1 2
3 KATY 3 Chicken 3 1 3
4 MILLER 4 Salad 4 2 1
5 AMANDA 5 Sushi 5 2 2
6 2 3
7 3 2
8 3 3
9 4 3
10 4 5
11 5 5
When the table is defined in this way, I want to arrange food tastes similar to Bob's. I'm doing it like this now.
SELECT people_id, COUNT(people_id) as count
FROM peopleFood
WHERE food_id IN
(SELECT food_id FROM peopleFood
WHERE people_id = 1)
AND people_id != 1
GROUP BY people_id
ORDER BY count DESC;
-- Result -------------
People_id | count
2 3
3 2
4 1
Is there a better way to change this method or use join? Thank you!!!
CodePudding user response：
Inner join:
SELECT p.People_id, COUNT(p.People_id) as count FROM PeopleTable p
INNER JOIN FoodTable f
ON(p.People_id = f.FoodId)
WHERE people = 1
GROUP BY p.people_id
ORDER BY count DESC;
If it helps, please mark it as an accepted answer!
CodePudding user response：
You have been inconsistent in your use of the table and column names -
Tables - PeopleFood in your sample data but you reference peopleFood in your query.
Columns - PeopleId and FoodId in your sample data but you reference people_id and food_id in your query.
Choose a naming convention and stick to it. Everyone has there own preference but the important thing is to be consistent.
The equivalent query with INNER JOIN instead of your sub-query is -
SELECT
`pf2`.`people_id`,
COUNT(`pf2`.`food_id`) as `count`
FROM `PeopleFood` `pf1`
INNER JOIN `PeopleFood` `pf2`
ON `pf2`.`people_id` <> `pf1`.`people_id`
AND `pf2`.`food_id` = `pf1`.`food_id`
WHERE `pf1`.`people_id` = 1
GROUP BY `pf2`.`people_id`
ORDER BY `count` DESC;
The performance difference between the two queries is unlikely to be noticeable and it might be argued that the intent is clearer in your version with the sub-query.
The surrogate key ID on your PeopleFood table should be dropped in favour of the compound “natural” primary key on people_id and food_id.