Question

I’m having a hard time describing this and it’s very possible that I am making this more difficult than it should be…

Basically, I have a page filled with pins/posts and users can upvote or downvote them. In one query, I want to get a list of the pins, but also join two tables to see if the user has upvoted or downvoted them.

The table structures:

pins table

|  id  |       title       |
+------+-------------------+
    1         Post 1
    2         Post 2
    3         Post 3
    4         Post 4

user_upvotes table

|  id  |  user_id  |  pin_id  |
+------+-----------+----------+
   1         1           2
   2         2           1
   3         2           3
   4         2           1

user_downvotes table

|  id  |  user_id  |  pin_id  |
+------+-----------+----------+
   1         2           2
   2         1           1
   3         1           3
   4         1           1

Here’s the query I have tried, but ends up duplicating the pins on the page.

SELECT pins.id AS pin_id, title, user_upvotes.id AS upvote, user_downvotes.id AS downvote
FROM pins
LEFT JOIN user_upvotes ON user_upvotes.pin_id = pins.id AND user_upvotes.user_id = 2
LEFT JOIN user_downvotes ON user_downvotes.pin_id = pins.id AND user_downvotes.user_id = 2

This results in (notice that pin_id 1 is repeated twice):

| pin_id |       title       |  upvote  |  downvote  |
|   1    |       Post 1      |  (NULL)  |      2     |
|   1    |       Post 1      |  (NULL)  |      4     |
|   2    |       Post 2      |     1    |    (NULL)  |
|   3    |       Post 3      |  (NULL)  |      3     |
|   4    |       Post 4      |  (NULL)  |    (NULL)  |

From this point I just check if the value is NULL and if not, I attach a css class to indicate that it has been upvoted or downvoted.

Essentially, I want the above results, just without the pin being duplicated. If you have a better way of doing this, feel free to let me know that as well.

Answer 1

Add GROUP BY

SELECT pins.id AS pin_id, title, user_upvotes.id AS upvote, user_downvotes.id AS downvote
FROM pins
LEFT JOIN user_upvotes ON user_upvotes.pin_id = pins.id AND user_upvotes.user_id = 2
LEFT JOIN user_downvotes ON user_downvotes.pin_id = pins.id AND user_downvotes.user_id = 2
GROUP BY pin_id