爲沒有找到任何內容的select語句定義返回參數

Question

這是我的select語句。它有什麼作用？

• 檢查是否有數據庫中已有的約會在指定日期的
• 檢查，如果用戶在特定時間的工作。

With mysql_num_rows($result)我檢查是否有任何行。如果返回0，則可以添加約會，如果返回其他內容（數據庫中已有約會），則會阻止該約會。

該聲明適用於第1點。如果已有約會，則返回1或更多。但是，當選定日期超出用戶的工作小時範圍時，它也返回0.

問題：我可以在聲明中添加什麼以獲取返回的行（mysql_num_rows返回1或更多），何時用戶在該特定時間不工作？

工作小時範圍示例：08:00:00 to 17:00:00。

select * 
from ios_appointments a join ios_workinghours h using(workerid_fk) 
where workerid_fk = 1 
AND h.start <= '19:57:20' AND h.end >= '20:57:20' 
AND ( 
    a.start BETWEEN '2012-12-24 19:57:20' AND '2012-12-24 20:57:20' 
    OR a.end BETWEEN '2012-12-24 19:57:20' AND '2012-12-24 20:57:20' 
    OR (a.start < '2012-12-24 19:57:20' AND a.end > '2012-12-24 20:57:20') 
) 

Answer 1

你可以返回空值的一行：

select * 
from ios_appointments a join ios_workinghours h using(workerid_fk) 
where workerid_fk = 1 
AND h.start <= '19:57:20' AND h.end >= '20:57:20' 
AND ( 
    a.start BETWEEN '2012-12-24 19:57:20' AND '2012-12-24 20:57:20' 
    OR a.end BETWEEN '2012-12-24 19:57:20' AND '2012-12-24 20:57:20' 
    OR (a.start < '2012-12-24 19:57:20' AND a.end > '2012-12-24 20:57:20') 
) 
union 
select null, null, null -- how every many column are in the first part 
where not exists (
    select * 
    from ios_appointments a join ios_workinghours h using(workerid_fk) 
    where workerid_fk = 1 
    AND h.start <= '19:57:20' AND h.end >= '20:57:20' 
    AND ( 
     a.start BETWEEN '2012-12-24 19:57:20' AND '2012-12-24 20:57:20' 
     OR a.end BETWEEN '2012-12-24 19:57:20' AND '2012-12-24 20:57:20' 
     OR (a.start < '2012-12-24 19:57:20' AND a.end > '2012-12-24 20:57:20') 
    ) 
) 

這將返回空值的一行，如果您的查詢找到什麼，或者現在如果行被發現行爲。

您可以返回所需的任何值而不是空值。