Question

因此，我有3个表涉及汽车，保证和事故。我想知道与其他人相比事故最多的车辆的品牌。

我已经尝试了很多方法，但是大多数情况下，我只会得到或退回所有品牌或注册次数最多的汽车品牌，而不是发生事故最多的汽车

这些是我的桌子

create table car(
    n_veic bigint not null,
    matric varchar(15) not null,
    pais_matric text not null,
    n_pess bigint not null,
    tipo text not null,
    cor text not null,
    brand text not null,
    modelo varchar(15),
    primary key(n_veic),
    unique(matric),
    foreign key (n_pess) references pessoa(n_pess)
);

create table ensurance(
    apolice bigint not null,
    segurado bigint not null,
    car bigint not null,
    datai date not null,
    dataf date not null,
    cobertura numeric(10,2) not null,
    primary key(apolice),
    unique(segurado, veiculo),
    foreign key (segurado) references pessoa(n_pess),
    foreign key (car) references car(n_veic)
);  

create table accident(
    n_acid bigint not null,
    pess_segura bigint not null,
    veic_seguro bigint not null,
    data date not null,
    local varchar(255) not null,
    descr text not null,
    primary key(n_acid),
    unique(n_acid, veic_seguro),
    foreign key (pess_segura,veic_seguro) references ensurance(segurado, car)

这是我尝试过的

SELECT marca
FROM veiculo NATURAL JOIN acidente
GROUP BY marca
HAVING count (distinct n_veic)>=ALL
    (SELECT count (distinct n_veic)
    FROM veiculo NATURAL JOIN acidente
    GROUP BY marca);

Answer 1

试试这个-

注意： 1.尽量避免使用NATURAL JOIN并使用特定的列引用。 2.重新考虑DISTINCT计数是否确实必要。

SELECT TOP 1 marca, COUNT(DISTINCT n_veic) 
FROM veiculo 
NATURAL JOIN acidente 
GROUP BY marca
ORDER BY COUNT(DISTINCT n_veic) DESC

Answer 2

我认为逻辑是：

select c.marca, count(*) as num_acidentes
from acidente a join
     car c
     on a.veic_seguro = c.n_veic
group by c.marca
order by num_acidentes desc;

您可以使用fetch first 1 row only或适用于数据库的任何内容来仅获取一行。

如何从另一个表中获得一个表中的最高外观值？

2 个答案: