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mysqlsqlgroup-bygroup-concathaving

MYSQL Select different records from same table

I am working on small school database and I need some help with selecting students that are only booked on different days in week 1 and week 2.

My table structure is like below:

ChildId    Day  Room  Week
=======    ===  ====  ====
  1        1     20    1
  1        2     20    1
  2        1     20    2
  3        1     20    1
  3        2     20    1
  3        1     20    2
=====     ===   ===   ===

I would like to get all the children that meet the following criteria:

  • ONLY booked in week two (This is ChildId 2 and I can get this from the following query)
  SELECT DISTINCT b.childid FROM booking b
        where b.childid NOT IN (SELECT childid FROM bookingtemplate WHERE weekno = 1)

I also need

  • all children in week two whose days are different then week one. That will be ChildID 3 as he is booked on Monday and Tuesday on Week 1 and on Monday on week 2.

I am unable to get the children whose days are different in both the weeks:

Thank you

Solution

  • You can do it with aggregation and the conditions in the HAVING clause:

    SELECT ChildId 
FROM booking
WHERE Week IN (1, 2)
GROUP BY ChildId
HAVING MIN(Week) = 2
    OR GROUP_CONCAT(DISTINCT CASE WHEN Week = 1 THEN Day END ORDER BY Day) <>
       GROUP_CONCAT(DISTINCT CASE WHEN Week = 2 THEN Day END ORDER BY Day);

    See the demo.