Question

我正在创建一个包含大量嵌套查询的SQL查询，我正在尝试使用CASE表达式，但它表现得非常奇怪。

这是我目前的询问：

select t.fpl_id, t.team_name,
sum(pf.points)as gwpts,
(
    select sum(transfers_malus)
    from gameweeks
    where gameweeks.team_id = t.id and gameweeks.number = g.number
)as malus,
(
    select sum(points)
    from player_fixtures as pfix
    where gw_number = g.number and pfix.player_id = CASE WHEN minutes_played > 0 THEN g.captain_id ELSE g.vice_captain_id END
)
as cpts,
 (
    select max(web_name)
    from players
    join player_fixtures on players.id = player_fixtures.player_id and gw_number = g.number
    where players.id = CASE WHEN player_fixtures.minutes_played > 0 THEN g.captain_id ELSE g.vice_captain_id END
) as captain_name,
array_agg(p.id) as lineup
from teams as t
join gameweeks as g on t.id  = g.team_id
join gameweeks_players as gp on gp.gameweek_id = g.id
join players as p on gp.player_id = p.id
join player_fixtures as pf on p.id = pf.player_id  and pf.gw_number = g.number
where t.id = 1
group by t.id, g.id
order by g.number asc

我遇到问题的一点是，当我在做一个案例陈述时，看看其中一名队员（队长）是否还没有根据“minutes_played”进行比赛：

(select sum(points)
    from player_fixtures as pfix
    where gw_number = g.number and pfix.player_id = CASE WHEN minutes_played > 0 THEN g.captain_id ELSE g.vice_captain_id END
) as cpts

和

 (
    select max(web_name)
    from players
    join player_fixtures on players.id = player_fixtures.player_id and gw_number = g.number
    where players.id = CASE WHEN player_fixtures.minutes_played > 0 THEN g.captain_id ELSE g.vice_captain_id END
) as captain_name,

当minutes_played确实大于0时，一切正常。但是，当它等于0时，它不会“返回”任何东西，并且在我的行中返回NULL。 minutes_played是一个整数，当我在player_fixtures上尝试使用以下脚本时，minutes_played = 0 my＆gt;评估工作，我得到了正确的“坏”。

DO LANGUAGE plpgsql $$
    BEGIN
        IF (select minutes_played from player_fixtures where gw_number = 19 and player_id = 266 ) > 0 THEN 
            RAISE NOTICE 'GOOD';
        ELSE
            RAISE NOTICE 'BAD';
        END IF;
    END;
$$;

我对这整个数据库的事情都很陌生，所以我可能犯了一个新手的错误，但我一直在尝试过去6小时而没有任何运气。有人能指出我正确的方向吗？

Answer 1

问题在于，当没有匹配的行时，sum()返回null，和不会与null进行比较。

相反，请使用exists()，例如：

where exists(select * from player_fixtures
    where gw_number = 19
    and player_id = 266 
    and minutes_played > 0)

或者您可以在存储过程中使用if exists(...) then。

Case表达式不会返回Postgres查询中的“else”值

1 个答案: