（1）select a.* from tb1 a left join tb2 b on a.id=b.id where 
a.name='1'
a.name='1'
（2）select * from (select a.* from tb1 a left join tb2 b on a.id=b.id) as d where name='1'
（3）建视图tbView :select a.* from tb1 a left join tb2 b on a.id=b.id
select * from tbView as d where name='1'
这三种写法执行效率一模一样，印象中应该第一种写法最快。