fruits表,包含水果 id、名字、价格
orders表,包含 id 和订单号(num)
使用普通sql语句
select fruits.id,name,price,num
from fruits,orders
where fruits.id=orders.id;
使用内连接查询语句(结果与上图相同)
select fruits.id,name,price,num
from fruits INNER JOIN orders
ON fruits.id=orders.id;
inner join语法是ANSI SQL的标准规范,使用inner join连接语法能够确保不会忘记连接条件
例如:
select f1.id,f1.name
from fruits AS f1,fruits AS f2
where f1.id = f2.id and f2.id = '01';
1.LEFT JOIN(左连接)
select fruits.id,orders.num
from fruits left outer join orders
on fruits.id=orders.id;
2.RIGHT JOIN(右连接)
select fruits.id,orders.num
from fruits right outer join orders
on fruits.id=orders.id;
select name,price,num
from fruits inner join orders
on fruits.id=orders.id AND fruits.price>4;