mySQl，查询：如何从数据库中自定义选择？

我有四个表：mySQl，查询：如何从数据库中自定义选择？

courses, allocate_rooms, rooms, departments

查询：

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

从查询我必须做出选择视图rooms.room_number，allocate_rooms.start-allocate.rooms_end;如果没有与该课程相关的数据，我必须显示“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"

如何重写上述查询？如果有人帮我找到解决方案。

来源

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

来源

2016-05-14 11:08:51 scaisEdge

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

更好地解释我不明白..请 – scaisEdge

我可能不得不使用别名来加入那些从数据库中选择时添加的列！正如我在我的问题中说的，我需要加入'allocate_rooms.start，allocate_rooms.end，rooms.room_number'，并且如果没有与这些值相关的值，它应该显示为'没有分配房间' – Hola

尝试我不知道这是否是你所需要的，但试试这个：

就可以使用解码为得到你所需要的。

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;

来源

2016-05-14 12:12:50

这里是解决方案：

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

来源

2016-05-15 06:06:50 Hola

mySQl，查询：如何从数据库中自定义选择？

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