SQL max,all 谢谢指导。 
                                                    通常没区别,效率上MAX()更高,但在有NULL值得时候有一定差异 比如 create table test ( id int null , name varchar(10) ) insert test select 1,'1'union select 3,'3' union select 2,'sad' union select null,'sad' 
select name from test where id>all(select id from test where name='sad') /* name 
*/ 
select name from test where id>(select MAX(id)from test where name='sad') /* name
                                                    
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