PostgreSQL如何与as一起使用

问题描述

有人知道为什么这行不通吗？我收到：错误：“ most_recent”或附近的语法错误

with most_recent as (SELECT MAX(public."Master_playlist".updated_at)
FROM public."Master_playlist")
SELECT * from public."Playlist"
JOIN public."Master_playlist_playlist" on public."Playlist".id = public."Master_playlist_playlist".playlist_id
JOIN public."Master_playlist" on public."Master_playlist_playlist".master_playlist_id = public."Master_playlist".id
WHERE public."Master_playlist".updated_at = most_recent;

假设要从Master_playlist获取最近的日期，然后使用该日期来选择Master_playlist来与内部查询一起加入

谢谢！ HM

解决方法

with子句创建派生表，您需要使用join或子查询从中选择表。您还需要为该列添加别名，以便以后可以引用它，如：

with most_recent as (
    SELECT MAX(updated_at) max_updated_at
    FROM public."Master_playlist"
)
SELECT * 
from public."Playlist"
JOIN public."Master_playlist_playlist" 
    on public."Playlist".id = public."Master_playlist_playlist".playlist_id
JOIN public."Master_playlist" 
    on public."Master_playlist_playlist".master_playlist_id = public."Master_playlist".id
WHERE public."Master_playlist".updated_at = (SELECT max_updated_at FROM most_recent)

但是在这里，使用行限制查询看起来更简单：

select ...
from (
    select *
    from public."Master_playlist"
    order by updated_at desc
    limit 1
) mp
inner join public."Master_playlist_playlist" mpp
    on mpp.master_playlist_id = mp.id
inner join public."Playlist" p
    on p.id = mpp.playlist_id