我有 3 个表:
推文:
CREATE TABLE tweets (
text_content VARCHAR(280) not null,
username VARCHAR(50) not null,
timestamp TIMESTAMP not null DEFAULT current_timestamp,
id UUID not null DEFAULT uuid_generate_v4(),
CONSTRAINT tweets_pk PRIMARY KEY (id)
);
喜欢:
CREATE TABLE likes (
username VARCHAR(50) not null,
timestamp TIMESTAMP not null default current_timestamp,
post_id UUID not null,
CONSTRAINT likes_pk PRIMARY KEY (username, post_id),
CONSTRAINT likes_post_id_fk FOREIGN KEY (post_id) REFERENCES tweets(id)
);
和转推
CREATE TABLE retweets (
username VARCHAR(50) not null,
timestamp TIMESTAMP not null default current_timestamp,
post_id UUID not null,
CONSTRAINT retweets_pk PRIMARY KEY (username, post_id),
CONSTRAINT retweets_post_id_fk FOREIGN KEY (post_id) REFERENCES tweets(id)
);
我需要一个查询,它会选择所有推文,以及它们的点赞和转发量。
我确实设法编写了一个有效的查询,但我认为我过于复杂了,希望听到更简单的解决方案!
最佳答案
您想在加入之前聚合。假设 join
键是 post_id
:
select t.*, l.likes, r.retweets
from tweets t left join
(select post_id, count(*) as likes
from likes
group by post_id
) l
on l.post_id = t.id left join
(select post_id, count(*) as retweets
from retweets
group by post_id
) r
on r.post_id = t.id;
关于sql - 复杂的 Join Query,Join 3 tables with multiple group bys,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51340059/