Question

我正在使用MySql。当我从表中选择多列时

responsible_id，标题

然后生成错误。所以我不会选择多列。请帮我解决这个问题。

 select id,
        title,
        responsible_id,
        project_id p_id,(select responsible_id,title from projects where p_id=projects.project_id) responsible_id,
        status,
        create_by,
        milestone_id from tasks

Answer 1

您不能以这种方式从相关子查询中选择多个列。

JOIN改为两个表，如下所示：

 select 
   t.id,
   t.title AS TaskTitle,
   t.responsible_id,
   p.project_id p_id,
   p.responsible_id,
   p.title AS ProjectTitle,
   t.status,
   t.create_by,
   t.milestone_id
from tasks AS t
INNER JOIN projects AS p ON t.p_id = p.project_id

选择时，操作数应包含1列mysql错误

1 个答案: