SELECT * FROM table1 LEFT
JOIN table2 ON table1.id=table2.id
JOIN table3 ON table3.id1=table2.id1
and (条件);
SELECT 列名 form 表名
insert into 表名(列1,列2...) values (值1,值2...)
update 表名 set 列=新值 where 列 = 旧值
delete from 表名 where 列=值
select 列名 from 表名 order by 列名
asc
升序:desc
like
group by
having