CODEWITHSUNDEEP
mysqlsql
frosty
frosty

Reputation: 2851

Select multiple columns in subquery

Is there a way to select multiple columns in a subquery? I want to select two columns username and dateline from the posts table (3rd and 4th line), and I don't want to make two separate subqueries. Or is there a way to do this with a join?

SELECT `topics`.`id` AS `id`, `title`, `unique_views`, `tags`.`name` AS `name`, `bg_color`, `text_color`,
    `username`, `avatar`, `color`,
    (select `username` from `posts` where `topic_id` = `topics`.`id` order by `dateline` desc) as lastpost_username,
    (select `dateline` from `posts` where `topic_id` = `topics`.`id` order by `dateline` desc) as lastpost_dateline,
    (select `vote` from `topic_votes` where `topic_id` = `topics`.`id` and `voter_id` = :voter_id) as user_vote,
    (select count(*) from `topic_votes` where `topic_id` = `topics`.`id` and `vote` = 1) -
    (select count(*) from `topic_votes` where `topic_id` = `topics`.`id` and `vote` = -1) AS vote_sum
FROM `topics`
INNER JOIN `tags` ON `tags`.`id` = topics.`tag_id`
INNER JOIN `users` ON `topics`.`poster_id` = `users`.`id`
INNER JOIN `user_groups` ON `users`.`group_id` = `user_groups`.`id`
INNER JOIN `posts` ON `posts`.`topic_id` = `topics`.`id`
ORDER BY `topics`.`dateline` DESC
LIMIT 50

Upvotes: 1

Views: 4034

Answers (2)

madjardi
madjardi

Reputation: 5929

NOTE: for postgresql.
I no found similar question for postgresql. I hope this give any idea|help for both

You can use LATERAL for this purpose pseudocode

without lateral

SELECT *, T1.ID, S1.name from (
    select *, (select id from mysubquery) as TID from myTable
) AS T1
LEFT JOIN subquery S1 ON (T1.TID=S1.ID)  -- for take name

with lateral

select *, TID.id, TID.name  
    from myTable, 
    LATERAL (select id, name from mysubquery) as TID

Upvotes: 1

Bernd Buffen
Bernd Buffen

Reputation: 15057

You can do it like this. You can join a derived table, but i cant testet:

SELECT `topics`.`id` AS `id`, `title`, `unique_views`, `tags`.`name` AS `name`, `bg_color`, `text_color`,
    `username`, `avatar`, `color`,
    new_table.lastpost_username,
    new_table.lastpost_dateline,
    (select `vote` from `topic_votes` where `topic_id` = `topics`.`id` and `voter_id` = :voter_id) as user_vote,
    (select count(*) from `topic_votes` where `topic_id` = `topics`.`id` and `vote` = 1) -
    (select count(*) from `topic_votes` where `topic_id` = `topics`.`id` and `vote` = -1) AS vote_sum
FROM `topics
LEFT JOIN (
        select `username`,`dateline` FROM `posts`  ORDER BY `dateline` DESC
) AS new_table ON `new_table`.`topic_id` = `topics`.`id`
INNER JOIN `tags` ON `tags`.`id` = topics.`tag_id`
INNER JOIN `users` ON `topics`.`poster_id` = `users`.`id`
INNER JOIN `user_groups` ON `users`.`group_id` = `user_groups`.`id`
INNER JOIN `posts` ON `posts`.`topic_id` = `topics`.`id`
ORDER BY `topics`.`dateline` DESC
LIMIT 50

Upvotes: 0

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