Mysql-此查询是什么意思? [英] Mysql-What does this query mean?

问题描述

我正在尝试理解一些查询

I'm trying to understand some queries

其中之一是

(select (@a) 
 from (select(@a:=0x00)
     ,(select (@a) 
       from (information_schema.schemata)
       where (@a) in (@a:=concat(@a,schema_name,'<br>'))
       )
 ) a
)

请给我解释一下吗?

推荐答案

无需过多解释，这是对会话变量的严重滥用.看起来 试图以相同的方式获取数据库名称的串联列表，而GROUP_CONCAT的分隔符为<br>；但它看起来非常不可靠.

Not much to explain, it is a horrendous abuse of session variables. It looks like it is trying to get a concatenated list of database names, in the same manner GROUP_CONCAT would with a delimiter of <br>; but it looks very unreliable.

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