Question

我想获取在x天和y天下订单的工人的名字。

select name
from worker,
     orders
 where worker.workerid = oders.workerid
   and date = x and date = y;

所以我只想让两天都下订单的工人。

Answer 1

in (x,y)将为您提供在至少两天内工作的工人。

尽管这里的工作人员将为那些工作了2天的人提供帮助。

group by name
having count(distinct date)=2

总而言之，您得到了想要的东西

select name
from worker,
     orders
 where worker.workerid = oders.workerid
   and date in (x,y)
group by name
having count(distinct date)=2

Answer 2

执行GROUP BY。使用HAVING确保两个日期都在那里。

select name
from worker
join orders
    on worker.workerid = orders.workerid
where date in (x, y)
group by name
having count(distinct date) >= 2

请注意切换到现代的显式JOIN语法！

Answer 3

使用两个where子句...

SELECT name 
FROM worker AS w
WHERE EXISTS (SELECT 1
    FROM orders AS o 
    WHERE w.workerid = o.workerid
    AND date = x)
AND EXISTS (SELECT 1
    FROM orders AS o 
    WHERE w.workerid = o.workerid
    AND date = y)

Answer 4

最简单的方法是使用2个部分查询和postgre Intersect运算符：

select name
from worker,
     orders
 where worker.workerid = oders.workerid
   and date = y
INTERSECT
select name
from worker,
     orders
 where worker.workerid = oders.workerid
   and date = x;

这将仅保留在X和y处于活动状态的工作人员名称。

http://www.postgresqltutorial.com/postgresql-intersect/

类似于UNION和EXCEPT运算符，PostgreSQL INTERSECT运算符将两个或多个SELECT语句的结果集合并为一个单个结果集。 INTERSECT运算子会传回在两个结果集中都可用，或两个查询都返回。

Answer 5

尝试一下：

SELECT name from worker, orders 
WHERE worker.workerid = oders.workerid
    DATE date IN (x, y)

如何在同一实体上使用AND？

5 个答案: