优化SQL查询以获取计数（*）

Question

I have the following query that gets some results I would like to group by attribute 'state'. I tried different subquery but they didn't work and I'm a bit blocked. The SQL is:

    SELECT state, id_candidate_basic, MAX( DATE )  FROM `candidate_state` 
    WHERE `date` <= '2013-09-06 00:00:00' GROUP BY id_candidate_basic
    ORDER BY `candidate_state`.`id_candidate_basic` DESC

This returns currently:

I would get a count(*) for each state. Example: F, 14 I, 10 O, 9

Answer 1

SELECT  state, 
        id_candidate_basic, 
        MAX( DATE ),
        COALESCE(totalCount, 0) totalCount
FROM    `candidate_state` 
        LEFT JOIN 
        (
            SELECT  state, COUNT(*) totalCount
            FROM    candidate_state
            WHERE   `date` <= '2013-09-06 00:00:00' 
            GROUP   BY state
        )   ON candidate_state.state = b.state
WHERE   `date` <= '2013-09-06 00:00:00' 
GROUP   BY id_candidate_basic
ORDER   BY `candidate_state`.`id_candidate_basic` DESC