Question

I have table with votes where data is written in this format:

id_user|id_user2|value
1|2|-1
1|3|1
5|3|1
2|1|-1

id_user is user who voted, id_user2 is user who got vote and value represents if he got positive or negative vote. Well and my problem is that i would like to show how stands each user in giving and getting votes in same output. Below is how i would like output from above input would look:

id_user|given|gotten
1|0|-1
2|-1|-1
3|0|2
5|1|0

I don’t know how to do this, i just know how i can show this with two separate queries. In this case it would be:

SELECT id_user2,SUM(value) FROM `table` GROUP BY id_user2

and

SELECT id_user,SUM(value) FROM `table` GROUP BY id_user

Answer 1

Simply join the queries :

SELECT
  gotten.id_user,
  gotten.gotten,
  given.given
FROM
(
  SELECT
    id_user2   AS id_user,
    SUM(value) AS gotten
  FROM
    table
  GROUP BY
    id_user2
) gotten
JOIN -- Join the current row with rows verifying...
(
  SELECT
    id_user,
    SUM(value) AS given
  FROM
    table
  GROUP BY
    id_user
) given ON given.id_user =  gotten.id_user -- ... this is the same user.

N.B. if the user did not give or did not get votes, it won’t return anything for him. If you need a result for these cases, use a full outer join to join even if there are not rows matching your condition in the left or right table.

SELECT
  gotten.id_user,
  gotten.gotten,
  given.given
FROM
(
  SELECT
    id_user2   AS id_user,
    SUM(value) AS gotten
  FROM
    table
  GROUP BY
    id_user2
) gotten
FULL OUTER JOIN -- Join the current row with rows verifying...
(
  SELECT
    id_user,
    SUM(value) AS given
  FROM
    table
  GROUP BY
    id_user
) given ON given.id_user =  gotten.id_user -- ... this is the same user.

You will get null values where there are no given or gotten votes.