Mysql query from one table with different conditions

Question

I would like to calculate every item's vote count for this table:

    user    item    vote
--------------------------------
    4       1       left
    4       2       left
    2       2       right
    3       2       left
    1       3       right

The result must be like this:

item | left_vote | right_vote
1       1               0
2       2               1
3       0               1

I've tried to use queries like this:

SELECT t.item, count(vote) as left_count, t.right_count  from (SELECT count(vote) as right_count, item from view where vote = 'right') as t, view where vote = 'left';

But it doesn't work. I think that I have to use join with subquery.

Is it real with mysql?

Answer 1

In MySQL you can just use conditional aggregation:

select item, sum(vote = 'left') as left_vote, sum(vote = 'right') as right_vote
from votes v
group by item;

You don't need a join or subquery for this.