Sql 如何使用联接获得单个结果?
使用postgres,我编写了以下SQL请求:Sql 如何使用联接获得单个结果?,sql,postgresql,Sql,Postgresql,使用postgres,我编写了以下SQL请求: SELECT projects.id , projects.title , comments.message as comment_message FROM "projects" RIGHT OUTER JOIN comments ON comments.project_id = projects.id GROUP BY projects.id, comments.message 我有这样的结果: id | t
SELECT projects.id
, projects.title
, comments.message as comment_message
FROM "projects"
RIGHT OUTER JOIN comments
ON comments.project_id = projects.id
GROUP BY projects.id, comments.message
我有这样的结果:
id | title | comment_message
----+----------------+-----------------
6 | simple project | simple comment
6 | simple project | simple message
有可能只有第一个结果吗?我只想有一个项目的结果
谢谢 你可以写:
SELECT projects.id,
projects.title,
MIN(comments.message) AS comment_message
FROM "projects"
RIGHT
OUTER
JOIN comments
ON comments.project_id = projects.id
GROUP
BY projects.id
;
你想要哪个结果?其他评论呢?是的,这是可能的,您必须根据您的需要使用评论消息字段进行过滤。我猜不出第一个结果在哪方面比第二个结果更受欢迎。