SQL执行顺序

创建外键约束
格式:alter table 从表 add [constraint 外键名称(自定义)] foreign key 从表(外键列名) references 主表(主键列名)
sql语句关键字的顺序
select 
from 
where 
group by 
having 
order by
执行顺序:
from 
where 
group by 
having 
select 
order by