MySQL：如何从数据库中选择下一行或上一行？

Question

I've got a table called " posts ", and within that table a column with " post_id " (A long with other columns ofc).

How to I select the next (or previous) row from the table, by " post_id "?

Let's say my current " post_id " is 15. Now I need to select the next row, where certain conditions are met, so I need to put in some where clauses.

I'm bad at explaining this I feel. I'm looking for something like this:

SELECT (next row) FROM posts WHERE post_draft=0 && post_approved=1

Can anybody help me with this?

Answer 1

Relational database system have no concept of a "next row" or "previous row". That is because there is no natural order of entries in such a database. So there terms "next" and "previous" are not really defined.

You can however implement a query that delivers what you are looking for:

SELECT * 
  FROM posts 
  WHERE post_id>15 
    AND post_draft=0 
    AND post_approved=1
  ORDER BY post_id ASC
  LIMIT 1;

So if you have the current post_id it is easy to pick the "next" entry according to a given order of a result set. The same is obviously possible for the "previous" entry.

Answer 2

I would use something like this.

$next_post_query = "SELECT * FROM `posts` WHERE `post_draft`=0 AND `post_approved`=1 AND `post_id` > {$current_post_id} order by `post_id` asc limit 1";
$prev_post_query = "SELECT * FROM `posts` WHERE `post_draft`=0 AND `post_approved`=1 AND `post_id` < {$current_post_id} order by `post_id` desc limit 1";

Answer 3

假设post_id列是自动递增的，则可以尝试

select * from posts where post_id in (select post_id+1 from posts where post_draft=0 and post_approved=1)