如何连接 2 个表并在 PostgreSQL 的第一个表中嵌套其他表的值列表？

Question

假设我们有这 2 个表：person 和 car

CREATE TABLE person (
    id BIGSERIAL NOT NULL PRIMARY KEY,
    name VARCHAR NOT NULL
);

CREATE TABLE car (
    id BIGSERIAL NOT NULL PRIMARY KEY,
    make VARCHAR NOT NULL,
    person_id BIGINT NOT NULL REFERENCES person(id)
);

我试图做的是找到所有人，找到每辆车并创建一个像这样的对象数组

[
    {
        "id": "PERSON_ID",
        "name": "PERSON_NAME",
        "cars": [
            {
                "id": "CAR_ID",
                "model": "MODEL_NAME",
                "person_id": "PERSON_ID"
            }
        ]
    }
]

我尝试在car 表中的person 表上使用AS 别名和JOIN，但它不起作用。有没有办法做到这一点？谢谢！

Answer 1

您可以尝试以下方法。看到一个工作小提琴：

架构 (PostgreSQL v13)

CREATE TABLE person (
    id BIGSERIAL NOT NULL PRIMARY KEY,
    name VARCHAR NOT NULL
);

CREATE TABLE car (
    id BIGSERIAL NOT NULL PRIMARY KEY,
    make VARCHAR NOT NULL,
    person_id BIGINT NOT NULL REFERENCES person(id)
);

insert into person(name) values ('tom'),('harry');

insert into car (id,make,person_id) values (1,'ford',1),(2,'audi',1),(3,'nissan',2);

---

查询 #1

SELECT
   p.id,
   p.name,
   array_agg(row_to_json(c)) cars
FROM
   person p
INNER JOIN
   (SELECT id, make model, person_id FROM car) c ON p.id = c.person_id
GROUP BY
   p.id,
   p.name;

id	name	cars
1	tom	[{"id":1,"model":"ford","person_id":1},{"id":2,"model":"audi","person_id":1}]
2	harry	[{"id":3,"model":"nissan","person_id":2}]

---

View on DB Fiddle

Answer 2

如果你想在 Postgres 中将结果集作为一个数组，你可以使用：

select p.*, array_agg(c)
from person p join
     car c
     on c.person_id = p.id
group by p.id;

如果你也想返回 JSON，你可以做类似的事情。