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下文会用到两张表:客户表和订单表。如下图所示:
客户表:
订单表:
内连接(inner join)
满足条件的记录才会出现在结果集中
隐式内连接:
select first_name, last_name, order_date, order_amount
from customers, orders
where customers.customer_id = orders.customer_id
显示内连接:
select first_name, last_name, order_date, order_amount
from customers c
inner join orders o
on c.customer_id = o.customer_id
结果集:
左外连接(left outer join,outer可省略)
左表全部出现在结果集中,若右表无对应记录,则相应字段为NULL
select first_name, last_name, order_date, order_amount
from customers c
left join orders o
on c.customer_id = o.customer_id
结果集:
右外连接(right outer join,outer可省略)
右表全部出现在结果集中,若左表无对应记录,则相应字段为NULL
select first_name, last_name, order_date, order_amount
from customers c
right join orders o
on c.customer_id = o.customer_id
结果集:
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全外连接(full outer join,outer可省略)
全外连接=左外连接+右外连接
select first_name, last_name, order_date, order_amount
from customers c
full join orders o
on c.customer_id = o.customer_id
结果集: