Question

晚上好！我有问题，因为我不能在WHERE中使用MAXGROWTHPARENT值 ORDER BY claused。我写了这个问题：

    SELECT PERSON.*, 
(
    SELECT MAX(PARENT.GROWTH) 
    FROM MAN PARENT
    WHERE 
        (PARENT.ID = PERSON.ID_FATHER)
    OR
        (PARENT.ID = PERSON.ID_MOTHER)  
) AS MAXGROWTHPARENT
FROM MAN PERSON
WHERE PERSON.GROWTH > 
(
    SELECT MAX(PARENT.GROWTH) 
    FROM MAN PARENT
    WHERE 
        (PARENT.ID = PERSON.ID_FATHER)
    OR
        (PARENT.ID = PERSON.ID_MOTHER)
)
ORDER BY (PERSON.GROWTH - 
    (
        SELECT MAX(PARENT.GROWTH) 
        FROM MAN PARENT
        WHERE 
            (PARENT.ID = PERSON.ID_FATHER)
        OR
            (PARENT.ID = PERSON.ID_MOTHER)
    )
);

我的代码看起来非常难看。你能告诉我如何使用MAXGROWTHPARENT吗？在WHERE和ORDER BY子句中？

Answer 1

我认为两个单独的连接可能会更好：

select p.*, greatest(pf.growth, pm.growth) as MAXGROWTHPARENT
from man p left join
     man pf
     on p.id_father = pf.id_father left join
     man pm
     on p.id_mother = pm.id_mother
order by p.growth - greatest(pf.growth, pm.growth);

注意：如果联接可能不匹配，您可能更喜欢：

select p.*, greatest(coalesce(pf.growth, pm.growth), coalesce(pm.growth, pf.growth)) as MAXGROWTHPARENT
from man p left join
     man pf
     on p.id_father = pf.id_father left join
     man pm
     on p.id_mother = pm.id_mother
order by p.growth - greatest(coalesce(pf.growth, pm.growth), coalesce(pm.growth, pf.growth));

POSTGRESQL：使用WHERE子句中的先前计算值

1 个答案: