select column1, column2 from TABLE1 join TABLE2 on 条件

#
select * from table1 join table2;
#两个表合成一个
select a.*, b.* from a left join b where a.id=b.id limit 0,1;

on 条件 where/ group by / having/ 
除了on的条件，　还能加where等条件

除了join还有:
left join　左表为准
right join　右表为准
inner join　交集

用法差不多