关系数据库查询

问题描述：

我将如何结合这些查询？ “已删除”字段是指示何时“删除”主题的时间戳。该主题并未真正被删除。如果它有实际的时间戳，我只是不会显示它。关系数据库查询

$topics = "SELECT id FROM topics WHERE deleted = '0000-00-00 00:00:00'"; 

$comments = "SELECT * FROM comments WHERE topic_id IN($topics)";

答

使用此解决方案：

SELECT a.* 
FROM comments a 
INNER JOIN topics b ON 
    a.topic_id = b.id AND 
    b.deleted = '0000-00-00 00:00:00'