使用外部连接的SQL查询？

Question

我有以下关系：

，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 

Answer 1

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';