我该如何重写这个查询，以避免错误：你不能在FROM子句中指定更新的目标表

Question

update websites set master = 2 where url = select url from websites where id = 12; 

显然mysql不会允许你在你正在更新的表上运行select查询。

Answer 1

把它放到派生表中。 This gets materialised into a temp table and gets around the restriction。

update websites 
set master = 2 
where url in (select url 
       from (select url 
         from websites 
         where id = 12) t); 

Answer 2

update websites set master = 2 where url in (select w2.url from websites w2 where w2.id = 12);