Sql 大小写表达式不返回；否则"；Postgres查询中的值

我正在创建一个包含大量嵌套查询的SQL查询，并尝试使用CASE表达式，但它的行为异常

这是我目前的问题：

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

我遇到的问题是，我在做案例陈述时，根据“上场分钟数”判断球员（队长）中是否有人没有上场：

及

当播放的分钟数确实大于0时，一切正常。然而，当它等于0时，它不会“返回”任何东西，并且我的行中会得到一个NULL。minutes_played是一个整数，当我在player_fixture上尝试使用以下脚本时，其中minutes_played=0，我的>评估有效，我得到了正确的“BAD”

---

我对DB这整件事还很陌生，所以我可能犯了一个新手错误，但在过去的6个小时里我一直在尝试，没有任何运气。有人能给我指出正确的方向吗？

问题是，当没有匹配的行时，

sum（）

返回null，与null的比较永远不会为真

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

（如果存在）（…），然后使用
。
如果您在case语句中使用别名会发生什么情况，例如，对于第一个：
当pfix.minutes\u播放时的case>0，然后g.captain\u id ELSE g.vice\u captain\u id END
@cha已在任何地方尝试使用别名，或者没有别名，但也不起作用：(
 (
    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,

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

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