Question

Is it possible to filter certain null values after left join using some conditions in mysql

my sqlfiddle for reference

http://sqlfiddle.com/#!2/cb03b/1

i want to return the tables with their status for a particular booked datetime i have added the date condition but its returning rows of booking of other dates with the status

is my table structure is wrong or is their a solution for it….

expected output for date December, 09 2012 00:00:00+0000

TABLE_ID FLOOR_ID TABLE_STATUS  BOOKING_ID         D
1         1        seated            35      December, 09 2012 00:00:00+0000
2         1        free           (null)    (null)
3         1        free           (null)    (null)
4         1        free           (null)    (null)
5         1        free           (null)    (null)

but i am getting other nulls from booking table

 TABLE_ID FLOOR_ID TABLE_STATUS BOOKING_ID  D
   1     1           seated       35    December, 09 2012 00:00:00+0000
   2     1                        (null)    (null)
   2     1                        (null)    (null)
   3     1            free        (null)    (null)
   4     1            free        (null)    (null)
   5     1            free        (null)    (null)

Answer 1

You can use Group By to do this, but it isn’t really clear what you want in the case of multiple matches for one table. You can use a combination of left outer join and inner join to ignore the unwanted booking_table rows:

Select
  t.table_id,
  t.floor_id,
  coalesce(Max(bt.table_status),'free') as table_status,
  max(bt.booking_id) as booking_id,
  max(bt.date) as d
From
  ttable as t
    Left Outer Join (
      Select
        bt.table_id,
        bt.table_status,
        b.booking_id,
        b.date
      From
        booking_table as bt 
          Inner Join
        booking As b
          On b.booking_id = bt.booking_id And b.date = '2012-12-09'
    ) bt On bt.table_id = t.table_id
Where
  t.floor_id = 1
Group By
  t.table_id,
  t.floor_id

You could use a right outer join to avoid the nesting, but it’s not generally recommended:

Select
  t.table_id,
  t.floor_id,
  coalesce(Max(bt.table_status),'free') as table_status,
  max(b.booking_id) as booking_id,
  max(b.date) as d
From
  booking_table as bt
    Inner Join
  booking b
    On b.booking_id = bt.booking_id And b.date = '2012-12-09'
    Right Outer Join
  ttable as t
    On bt.table_id = t.table_id
Where
  t.floor_id = 1
Group By
  t.table_id,
  t.floor_id

http://sqlfiddle.com/#!2/cb03b/20