MySQL left join on和where的常见问题

select * from base_student s left join base_class c on s.class_id=c.id and s.name="张三" order by s.id

-- where的作用是在处理临时表生效

select * from base_student s left join base_class c on s.class_id=c.id where s.name="张三" order by s.id