mySQl，查詢：如何從數據庫中自定義選擇？

我有四個表：mySQl，查詢：如何從數據庫中自定義選擇？

courses, allocate_rooms, rooms, departments

查詢：

SELECT 
    courses.`name`, 
    courses.`code`, 
    allocate_rooms.`start`, 
    allocate_rooms.`end`, 
    rooms.room_number 
FROM 
    departments 
JOIN courses ON departments.id = courses.department_id 
LEFT JOIN allocate_rooms ON allocate_rooms.course_id = courses.id 
LEFT JOIN rooms ON allocate_rooms.room_id = rooms.id 
WHERE 
    departments.id = 1

從查詢我必須做出選擇視圖rooms.room_number，allocate_rooms.start-allocate.rooms_end;如果沒有與該課程相關的數據，我必須顯示「尚未安排」。

Eg: R.No: 301,12:00-12:30; (if the course related data is there otherwise it will show "Not Scheduled Yet"

如何重寫上述查詢？如果有人幫我找到解決方案。

來源

2016-05-14 Hola

你可以用IFNULL

SELECT courses.name, courses.code, allocate_rooms.start, 
    allocate_rooms.end , 
    case rooms.room_number 
     WHEN IS NULL THEN 'No Rooms allocated' 
     WHEN 0 THEN 'No Rooms allocated' 
     ELSE room.room_number 
     end 
FROM departments 
join courses on departments.id = courses.department_id 
left join allocate_rooms on allocate_rooms.course_id=courses.id 
left join rooms on allocate_rooms.room_id=rooms.id 
WHERE departments.id=1

來源

2016-05-14 11:08:51 scaisEdge

我如何加入'rooms.room_number，allocate_rooms.start -allocate_rooms.end的視圖;' – Hola

更好地解釋我不明白..請 – scaisEdge

我可能不得不使用別名來加入那些從數據庫中選擇時添加的列！正如我在我的問題中說的，我需要加入'allocate_rooms.start，allocate_rooms.end，rooms.room_number'，並且如果沒有與這些值相關的值，它應該顯示爲'沒有分配房間' – Hola

嘗試我不知道這是否是你所需要的，但試試這個：

就可以使用解碼爲得到你所需要的。

SELECT 
    c.name name 
    ,c.code code 
    ,decode(ar.start,NULL,'Not Schedule Yet') START 
    ,decode(ar.end,NULL,'Not Schedule Yet') END 
    ,r.room_number roomnum 
FROM 
    departments d 
    ,courses c 
    ,allocate_rooms ar 
    ,rooms r 
WHEREd.id = c.id 
AND ar.course_id = c.id 
AND ar.room_id = r.room_id 
AND d.id = 1;

來源

2016-05-14 12:12:50

這裏是解決方案：

SELECT courses.name, courses.code,COALESCE(CONCAT('R. No',':',rooms.room_number,', ',days.name ,', ', allocate_rooms.start,' - ',allocate_rooms.end),"Not Assigned Yet") AS Schedule 
FROM departments join courses on departments.id = courses.department_id 
left join allocate_rooms on allocate_rooms.course_id=courses.id 
left join rooms on allocate_rooms.room_id=rooms.id 
left join days on allocate_rooms.day_id=days.id WHERE departments.id=1

來源

2016-05-15 06:06:50 Hola

mySQl，查詢：如何從數據庫中自定義選擇？

回答

相關問題