SQL 添加列答案

【问题标题】：SQL adding columnsSQL 添加列
【发布时间】：2017-10-03 13:47:02
【问题描述】：

我对两列求和的基本操作有疑问。这很简单，但它不起作用。

我得到结果 5 + 5 = 8, 3 + 7 = 7

这是查询：

select 
    `wp_posts`.ID ,
    (select count(*) from `co_likes` 
     where `wp_posts`.`ID` = `co_likes`.`id_post` 
       and `co_likes`.`deleted_at` is null) as `like_count`, 
    (select count(*) from `wp_comments` 
     where `wp_posts`.`ID` = `wp_comments`.`comment_post_ID`) as `comment_count` ,
    (`comment_count`+`like_count`) as 'total_sum'
from 
    `wp_posts` 
where 
    `post_type` in ('post', 'co_post') 
    and `post_status` = 'publish' 
order by 
    (comment_count+like_count) desc;

结果如下：

知道发生了什么吗？

【问题讨论】：

你不能使用之前在同一个查询中定义的列别名。我不确定这个查询最初是如何运行的。

标签： mysql sql mariadb

【解决方案1】：

您不能在定义它们的同一select（或where）中使用列别名。在您的情况下，最好的可能是子查询：

select p.*, (`comment_count`+`like_count`) as total_sum
from (select `wp_posts`.ID ,
             (select count(*) from `co_likes` where `wp_posts`.`ID` = `co_likes`.`id_post` and `co_likes`.`deleted_at` is null) as `like_count`, 
             (select count(*) from `wp_comments` where `wp_posts`.`ID` = `wp_comments`.`comment_post_ID`) as `comment_count` ,
      from `wp_posts` 
      where `post_type` in ('post', 'co_post') and `post_status` = 'publish' 
     ) p
order by total_sum desc;

如果只想按总和排序，不需要看，可以把总和放在order by：

      select `wp_posts`.ID ,
             (select count(*) from `co_likes` where `wp_posts`.`ID` = `co_likes`.`id_post` and `co_likes`.`deleted_at` is null) as `like_count`, 
             (select count(*) from `wp_comments` where `wp_posts`.`ID` = `wp_comments`.`comment_post_ID`) as `comment_count` ,
      from `wp_posts` 
      where `post_type` in ('post', 'co_post') and `post_status` = 'publish' 
      order by (like_count + comment_count) desc

【讨论】：