使 SQL 查询使用子查询从两个表中返回数据

Question

我需要从汽车表中返回汽车 ID 号，并从角色表中返回车主的姓名和姓氏。

每个角色都有一辆汽车，一个角色可以有多辆汽车。

我制作了 SQL 但它返回了分配给每个角色的每辆车。

SELECT a.id_number, b.owners 
FROM (
    SELECT number as id_number 
    FROM car 
    WHERE fk_ipasnieks IN (SELECT pk_kods FROM personas)
) as a,
(
    SELECT concat(name, ' ', surname) as owners 
    FROM personas 
    WHERE pk_kods IN (SELECT fk_ipasnieks FROM car)
) as b

Answer 1

子查询需要返回用于关联两个表的列。 否则，您将获得一个完整的交叉产品，将每个车主与每辆车配对。

SELECT a.id_number, b.owners 
FROM (
    SELECT fk_ipasnieks, number as id_number 
    FROM car 
    WHERE fk_ipasnieks IN (SELECT pk_kods FROM personas)
) as a
JOIN (
    SELECT pk_kods, concat(name, ' ', surname) as owners 
    FROM personas 
    WHERE pk_kods IN (SELECT fk_ipasnieks FROM car)
) as b ON a.fk_ipasnieks = b.pk_kods

这通常不会使用子查询来完成。 通常的写法是直接加入表。

SELECT c.number AS id_number, concat(p.name, ' ', p.surname) AS owner
FROM car AS c
JOIN personas as p ON c.fk_ipasnieks = p.pk_kods