MySQL条件分组

Question

The below data shows time schedule having elective/ non-elective subjects of a student. My requirement is to select those rows when both elec and nonelec type has same period so in this case select elec type.

Means for a day's schedule elective (type elec) should be given preference when both having same period. And when type elec does not has period like period 5 then select the non-elective one.

My Query

SELECT s.sch_id, s.sch_subtype, sd.sdetail_id, sd.sdetail_period
FROM schedule s
INNER JOIN schedule_detail sd ON s.sch_id = sd.sdetail_schedule
WHERE  '2014-04-30'
BETWEEN sch_datefrom
AND sch_dateto
AND 
(
  (
    sch_section =1
    AND sch_subtype =  'nonelec'
  )
  OR 
  (
    sch_subtype =  'elec'
    AND 272 
    IN 
    (    
      SELECT edetail_stuid
      FROM elective_detail
      WHERE edetail_elective = sch_section
    )
  )
)
AND sch_course =3
AND sch_batch =2
AND sch_termid =2
AND sdetail_day =  'wed'
AND sdetail_period >0
AND CASE WHEN sch_subtype =  'nonelec'
THEN 1 =1
WHEN sch_subtype =  'elec'
THEN sdetail_subject >0
AND sdetail_faculty >0
AND sdetail_room >0
END GROUP BY CASE WHEN sch_subtype =  'elec'
THEN sdetail_period
ELSE 1 
END ORDER BY sdetail_period

Output of above query

Required Output

Answer 1

You can try something of this sort :

SELECT sch_id,sch_subtype,sdetail_id,sdetail_period 
FROM table 
WHERE condition 
group by sch_subtype

It would be better if you can post the query which u tried.

Answer 2

Dont really get whats the problem here:

SELECT * FROM schedule s
JOIN schedule_detail sd ON s.sch_id = sd.sdetail_schedule
LEFT JOIN elective_detail ed ON sd.sch_section = ed.edetail_elective
WHERE
(
  sd.sch_section =1
  AND s.sch_subtype =  'nonelec'
)
OR
(
  ed.edetail_stuid = 227
  AND sch_subtype =  'elec'
)
GROUP BY sd.sdetail_period

SQL Fiddle: http://sqlfiddle.com/#!2/69d4e/1