选择两个表并按日期排序

Question

我正在尝试列出两个表doc_to_do的最新更新，下面的doc_bug_tracker是我的表结构

doc_to_do

doc_bug_tracker

这是我当前的查询：

$sth = $this->db->prepare('SELECT p.*, 
        dtd.projects_id as dtd_projects_id, dtd.content as dtd_content, dtd.date_modified as dtd_date_modified,
        dbt.projects_id as dbt_projects_id, dbt.content as dbt_content, dbt.date_modified as dbt_date_modified 
        FROM `projects` p LEFT JOIN `doc_to_do` dtd ON p.id=dtd.projects_id 
        LEFT JOIN `doc_bug_tracker` dbt ON p.id=dbt.projects_id 
        where p.id="'.$project_id.'"');

现在如何从表date_modified或doc_to_do doc_bug_tracker订购？

Answer 1

要获取 最新日期（而不是所有日期，按顺序降序），请尝试以下操作：

SELECT
  p.id,
  MAX(GREATEST(dtd.date_modified, dbt.date_modified)) AS MaxDate
FROM projects p
LEFT JOIN doc_to_do dtd ON p.id = dtd.projects_id
LEFT JOIN doc_bug_tracker dbt ON p.id = dbt.projects_id
WHERE p.id = <project_id>
GROUP BY p.id

如果您需要在SELECT中添加其他列，请务必将其添加到GROUP BY。

Answer 2

这应该有效：

'SELECT x.* FROM 
(
    SELECT p.*, 
        dtd.projects_id as dtd_projects_id, dtd.content as dtd_content, dtd.date_modified as dtd_date_modified,
        dbt.projects_id as dbt_projects_id, dbt.content as dbt_content, dbt.date_modified as dbt_date_modified 
        FROM `projects` p LEFT JOIN `doc_to_do` dtd ON p.id=dtd.projects_id 
        LEFT JOIN `doc_bug_tracker` dbt ON p.id=dbt.projects_id 
        where p.id="'.$project_id.'"
) x
ORDER BY x.date_modified ASC'