使用外部连接的SQL查询?
问题描述:
我有以下关系:使用外部连接的SQL查询?
,我想列出加入该公司的2014年6月之前,但在2014年6月使用某种外连接没有收到佣金的所有员工。我想出了这个查询,但它不起作用。有人可以告诉我如何查询这个?
SELECT DISTINCT Employee.EmpId, Employee.EmpName
FROM Employee
LEFT OUTER JOIN Commission
ON Employee.EmpId = Commission.EmpId
WHERE Employee.JoinDate BETWEEN Employee.JoinDate AND '2014-06-31'
GROUP BY Employee.EmpId, Employee.EmpName
HAVING COUNT(Commission.Commdate BETWEEN '2014-06-01' AND '2014-06-31') = 0
ORDER BY Employee.EmpId
答
该LEFT JOIN
是一个好主意。但是,您需要ON
条款中的佣金日期。然后找到不匹配的员工。所以,这里是一个版本的查询(清理使用表的别名):
SELECT e.EmpId, e.EmpName
FROM Employee e LEFT OUTER JOIN
Commission c
ON e.EmpId = c.EmpId AND
c.Commdate BETWEEN '2014-06-01' AND '2014-06-31'
WHERE e.JoinDate < '2014-06-01' AND c.EmpID IS NULL
GROUP BY e.EmpId, e.EmpName
ORDER BY e.EmpId;
也许更自然的方式来编写查询,虽然是:
SELECT e.*
FROM employee e
WHERE NOT EXISTS (SELECT 1
FROM Commission c
WHERE e.EmpId = c.EmpId AND
c.Commdate BETWEEN '2014-06-01' AND '2014-06-31'
) AND
e.JoinDate < '2014-06-01';
谢谢你,这使得它真的很清楚。 –