Question

    SELECT
        p.id AS id,
        json_agg((SELECT x FROM (SELECT 
            c.id, 
            c.name, 
            json_agg((SELECT y FROM (SELECT s.id, s.name) y)) AS js2
            ) x)) AS js1
    FROM p
    INNER JOIN s ON s.id = p.s_id
    INNER JOIN c ON c.s_id = p.s_id
    INNER JOIN cc ON c.id = cc.c_id AND p.c_id = cc.c_id
    GROUP BY p.c_id;

我想像这样聚合我的sql，但psql不允许我做js2。

错误：聚合函数调用不能嵌套json_agg（（SELECT y FROM（SELECT s.id，...

我该如何避免这种情况？

Answer 1

尝试将js2中的json_agg更改为row_to_json

 SELECT
        p.id AS id,
        json_agg((SELECT x FROM (SELECT 
            c.id, 
            c.name, 
            row_to_json((SELECT y FROM (SELECT s.id, s.name) y)) AS js2
            ) x)) AS js1
    FROM p
    INNER JOIN s ON s.id = p.s_id
    INNER JOIN c ON c.s_id = p.s_id
    INNER JOIN cc ON c.id = cc.c_id AND p.c_id = cc.c_id
    GROUP BY p.c_id;

-HTH

PostgreSQL避免嵌套聚合函数

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