Question

我有帖子，滑动，通知。我想

按照分数对帖子进行排序
删除刷过的
通过帖子加入通知，并将加入的通知作为最高分

到目前为止，我已完成前两个但无法将通知添加为结果的第一个元素。这是前两个的工作查询。

SELECT posts.id, posts.created_at, posts.data, ((posts.data)->>'score')::NUMERIC as score
FROM  posts
WHERE NOT EXISTS (
    SELECT  *
    FROM    swipes
    WHERE   ((swipes.data)->>'post_id')::INT = posts.id AND ((swipes.data)->>'user_id')::INT = 32)
ORDER BY (data)->>'score' 
LIMIT 5

我尝试LEFT JOIN添加通知，但无法执行此操作。

SELECT posts.id, posts.created_at, posts.data, ((posts.data)->>'score')::NUMERIC as score
FROM  posts
WHERE NOT EXISTS (
    SELECT  *
    FROM    swipes
    WHERE   ((swipes.data)->>'post_id')::INT = posts.id AND ((swipes.data)->>'user_id')::INT = 32)

-- The part below is new
UNION  ALL
SELECT notifications.id, notifications.created_at, notifications.data, 9999999 AS score
FROM   notifications

--- THIS GIVES ERROR ---
LEFT   JOIN posts USING (notifications.data)->>'post_id') 

WHERE  ((notifications.data)->>'user_id')::INT = 32

-- After join order by score
ORDER BY score 
LIMIT 5

通知有一个名为data类型json的列。 notifications.data->post_id应由posts.id加入，分数为9999999.其中notifications.data->user_id应等于32。

Answer 1

如果您想要来自表格＆＃39;通知＆＃39;的行除了表格＆＃39;帖子中的行之外，你应该UNION：

SELECT id, created_at, data, (data->>'score')::numeric AS score
FROM posts
WHERE NOT EXISTS (
    SELECT 1
    FROM swipes
    WHERE ((swipes.data)->>'post_id')::int = posts.id
      AND ((swipes.data)->>'user_id')::int = 32)

UNION  ALL

SELECT id, created_at, data, 9999999 AS score
FROM notifications
LEFT   JOIN posts USING (notifications.data)->>'post_id')
WHERE (data->>'user_id')::int = 32

-- After join order by score
ORDER BY score 
LIMIT 5;

如果您想要添加表格列的通知＆＃39;对于表格的帖子，你应该JOIN：

SELECT p.id, p.created_at, p.data, (p.data->>'score')::numeric AS score
       n.id, n.created_at, n.data 
FROM posts p
JOIN notifications n ON n->>'post_id' = p->>'post_id' -- guessing here
WHERE NOT EXISTS (
    SELECT 1
    FROM swipes
    WHERE ((swipes.data)->>'post_id')::int = p.id
      AND ((swipes.data)->>'user_id')::int = 32)
WHERE (n.data->>'user_id')::int = 32
ORDER BY score 
LIMIT 5;

Postgres JSON加入，联盟

1 个答案: