mysql - 存储过程返回错误值？

Question

我有一个存储过程来检查在我的数据库中预订的假期，它不应该考虑状态为“已拒绝”或“已取消”的假期，但我的数据库中只有一个记录拒绝状态但此选择语句返回 1？

        SELECT COUNT(*) JobRoleID
        FROM        Employees
        RIGHT JOIN  Holidays
        ON          Employees.ID = Holidays.EmployeeID
        WHERE       Holidays.Status <> 'Declined' AND Holidays.Status <> 'Cancelled'
        AND        (Holidays.Startdate <= '2014/04/28' AND Holidays.Enddate >= '2014/04/30')
        OR         (Holidays.Startdate >= '2014/04/28' AND Holidays.Enddate <= '2014/04/30') 
        OR         (Holidays.Startdate <= '2014/04/30' AND Holidays.Enddate >= '2014/04/30') 
        OR         (Holidays.Startdate <= '2014/04/28' AND Holidays.Enddate >= '2014/04/28') 
        OR         (Holidays.StartDate = '2014/04/28' AND Holidays.EndDate = '2014/04/30')

Answer 1

这里需要考虑运算符的优先级。

Not -->  AND --> OR 

Not 优先于 AND ，AND 优先于 OR。对于这些嵌套的 AND 和 OR，最好将它们放在括号中。

WHERE       Holidays.[Status] <> 'Declined' AND Holidays.[Status] <> 'Cancelled'
AND    
    (       (Holidays.Startdate <= '2014/04/28' AND Holidays.Enddate >= '2014/04/30')
        OR  (Holidays.Startdate >= '2014/04/28' AND Holidays.Enddate <= '2014/04/30') 
        OR  (Holidays.Startdate <= '2014/04/30' AND Holidays.Enddate >= '2014/04/30') 
        OR  (Holidays.Startdate <= '2014/04/28' AND Holidays.Enddate >= '2014/04/28') 
        OR  (Holidays.StartDate = '2014/04/28' AND Holidays.EndDate = '2014/04/30')
    )

如果在 sql 中使用方括号 [] 时，也请避免使用 Sql server 关键字作为列名。