Wordpress mysql group by |通過

Question

$post = $wpdb->get_results("SELECT `p`.`ID`, MAX(p.post_date) as `datetime`, `p`.`post_date`, `p`.`post_content`, `p`.`post_title`, `p`.`post_status`, `p`.`post_name`, `p`.`comment_count`, `tax`.`term_taxonomy_id`, `tax`.`term_id`, `tax`.`taxonomy`, `tax`.`parent`, `rel`.`object_id`, `rel`.`term_taxonomy_id`, `t`.`term_id`, `t`.`name`, `t`.`slug` 

FROM (`$wpdb->posts` AS p) 

INNER JOIN `$wpdb->term_relationships` AS rel ON `rel`.`object_id` = `p`.`ID` 

INNER JOIN `$wpdb->term_taxonomy` AS tax ON `tax`.`term_taxonomy_id` = `rel`.`term_taxonomy_id` 

INNER JOIN `$wpdb->terms` AS t ON `t`.`term_id` = `tax`.`term_id` 

WHERE `tax`.`taxonomy` = 'category' 
AND `p`.`post_status` = 'publish' 
AND `p`.`post_type` = 'post' 

GROUP BY tax.parent 

ORDER BY datetime DESC 
LIMIT 4"); 

$post = $wpdb->get_results("SELECT `p`.`ID`, MAX(p.post_date) as `datetime`, `p`.`post_date`, `p`.`post_content`, `p`.`post_title`, `p`.`post_status`, `p`.`post_name`, `p`.`comment_count`, `tax`.`term_taxonomy_id`, `tax`.`term_id`, `tax`.`taxonomy`, `tax`.`parent`, `rel`.`object_id`, `rel`.`term_taxonomy_id`, `t`.`term_id`, `t`.`name`, `t`.`slug` 

FROM (`$wpdb->posts` AS p) 

INNER JOIN `$wpdb->term_relationships` AS rel ON `rel`.`object_id` = `p`.`ID` 

INNER JOIN `$wpdb->term_taxonomy` AS tax ON `tax`.`term_taxonomy_id` = `rel`.`term_taxonomy_id` 

INNER JOIN `$wpdb->terms` AS t ON `t`.`term_id` = `tax`.`term_id` 

WHERE `tax`.`taxonomy` = 'category' 
AND `p`.`post_status` = 'publish' 
AND `p`.`post_type` = 'post' 

GROUP BY tax.parent 

ORDER BY datetime DESC 
LIMIT 4"); 

我需要找到每個類別的最新帖子，然後對結果進行分組，因此我只爲每個類別提供一個最新帖子。

我用的; GROUP BY tax.parent不起作用; ORDER BY datetime DESC

Answer 1

您的ID是遞增的。使用它。

select ... 
from 
..... 
where id post_in 
(select max(post_id) from table group by category) 

，如果你知道有多少種類有，你甚至更好的使用

where post id in 
(select post_id from table where category=1 order by time desc limit 1 
union 
select post_id from table where category=2 order by time desc limit 1 
union 
select post_id from table where category=3 order by time desc limit 1 
union 
select post_id from table where category=4 order by time desc limit 1) 

可以做到這一點，或者你可以使用參數，這將給你一個完美的結果，而是一個非常緩慢的查詢

select * from 
(select 
@rn:=if(@prv=category_id, @rn+1, 1) as rId, 
@prv:=category_id as category_id, 
timestamp, 
other columns 
from (select category_id, timestamp, other columns from ...)a 
join 
(select @prv:=0, @rn:=0)tmp 
order by 
category_id , timestamp desc) a 
where rid<=1 

Answer 2

嘗試GROUP BY t.name而不是tax.parent和MAX(p.ID)而不是MAX(p.post_date)。我不認爲你可以在日期時間使用MAX（可能是錯誤的，但它不適合我），我認爲按t.name分組是你想要的（或t.term_id或slug）。

它似乎給了我每個類別的最新帖子，但對我而言可能是巧合。