MySQL子查询返回多行并出错

我这里有一个SQL语句，我需要将特定列中的行划分为行。。。但当我检索数据时，返回的是错误

1子查询返回超过1行

：（请帮忙这是我的问题

(select 
    (SELECT 
            (meta_value)
        FROM
            main_postmeta
        WHERE
            meta_key = 'project_year') as Year,
    (SELECT 
            (meta_value)
        FROM
            main_postmeta
        WHERE
            meta_key = 'project_gapp_city') as Location,
    (SELECT 
            (meta_value)
        FROM
            main_postmeta
        WHERE
            meta_key = 'project_title') as Title
FROM
    main_postmeta
WHERE
    main_postmeta.post_id = '1423'
ORDER BY meta_value desc);

---

您似乎正在寻找数据透视结果集

select 
     case when meta_key='project_year' then meta_value else null end as `YEAR`
   , case when meta_key='project_gapp_city' then meta_value else null end as `LOCATION`
   , case when meta_key='project_title' then meta_value else null end as `Title`
from main_postmeta
where main_postmeta.post_id = '1423'
order by meta_value desc

如果取数分组在单个

post\u id

下，则：

select 
     max ( case when meta_key='project_year' 
                     then meta_value 
                else null 
           end ) as `YEAR`
   , max ( case when meta_key='project_gapp_city' 
                     then meta_value 
                else null
           end ) as `LOCATION`
   , max ( case when meta_key='project_title' 
                     then meta_value 
                else null
           end ) as `Title`
from main_postmeta
where main_postmeta.post_id = '1423'
 order by meta_value desc

---

可能最好对每个元值进行联接，如下所示：-

SELECT a.meta_value, b.meta_value, c.meta_value
FROM main_postmeta a 
INNER JOIN main_postmeta b ON a.post_id = b.meta_key AND b.meta_key = 'project_gapp_city'
INNER JOIN main_postmeta c ON a.post_id = c.meta_key AND c.meta_key = 'project_title'
WHERE a.post_id = '1423' 
AND a.meta_key = 'project_year'
ORDER BY meta_value DESC

SELECT GROUP_CONCAT(CONCAT_WS('|', meta_key, meta_value))
FROM main_postmeta a 
WHERE a.post_id = '1423' 
AND a.meta_key IN ( 'project_gapp_city', 'project_year', 'project_title')

根据您希望对结果执行的操作，您也可以执行以下操作：-

SELECT a.meta_value, b.meta_value, c.meta_value
FROM main_postmeta a 
INNER JOIN main_postmeta b ON a.post_id = b.meta_key AND b.meta_key = 'project_gapp_city'
INNER JOIN main_postmeta c ON a.post_id = c.meta_key AND c.meta_key = 'project_title'
WHERE a.post_id = '1423' 
AND a.meta_key = 'project_year'
ORDER BY meta_value DESC

SELECT GROUP_CONCAT(CONCAT_WS('|', meta_key, meta_value))
FROM main_postmeta a 
WHERE a.post_id = '1423' 
AND a.meta_key IN ( 'project_gapp_city', 'project_year', 'project_title')

---

然后分解出键和值。

根据错误，子查询只能包含一行，这在您查看时也是有意义的-想象一下，如果第一个子查询返回0行，第二个子查询返回1，第三个子查询返回30，会发生什么情况。如果没有表、数据和您期望的内容，则无法正确地帮助您。也许您应该询问该任务以你尝试的方式、你所期望的和你的数据的样子来考虑。考虑提供适当的DDL（和/或SqLFIDLE）。以及所需的结果集。请提供带有一些示例数据和预期输出的表格。我可能怀疑您需要检查每个子查询中的main_postETA.post_id的值。哇，工作得很有魅力谢谢很多朋友你救了我一天：）谢谢，伙计，它就像一个魔咒一样，我只是没想到它会在盒子外面哈哈：）谢谢你，一个磨坊！！