postgresql - Postgres 更新语句

Question

我已经从 mysql 转移到 psql，但是发现使用多个左连接很难理解 UPDATE 语句。

你将如何在 Postgres 中重写它？（我使用的是 postresql 9.4）

update task t 
    left join project p on t.project_id = p.id 
    left join client c on t.client_id = c.id 
    left join user u on t.user_id = u.id
set t.project_name = p.name, 
     t.client_name = c.name,
     t.user_name = u.name;

欢迎任何指针。

Answer 1

干得好：

WITH task_data AS (
    SELECT t.id,
        p.name AS project_name,
        c.name AS client_name,
        u.name AS user_name
    FROM task t 
        LEFT JOIN project p ON t.project_id = p.id 
        LEFT JOIN client c ON t.client_id = c.id 
        LEFT JOIN "user" u ON t.user_id = u.id
)
UPDATE task t
FROM task_data d
SET
    project_name = d.project_name, 
    client_name = d.client_name,
    user_name = d.user_name
WHERE t.id = d.id

我很想知道是否有更有效的方法