Question

I am having a bit of an issue with nested CASE in MySQL.

The rest_opening_hours table is as follows:

rest_opening_hours (
  restid int,
  day_of_week int,
  hours_open time,
  hours_close time,
)

I am then trying to perform a query. The reason for the WHEN DAYOFWEEK( NOW()) = 1 bit is that I notice that if you try to take away on a Sunday (day 1) it just returns 1, which causes issues.

SELECT h.hours_close
FROM restaurants s
INNER JOIN rest_opening_hours h
ON s.id = h.restid
WHERE 
CASE 
    WHEN h.hours_close > h.hours_open
    THEN h.day_of_week = DAYOFWEEK(NOW()) 
ELSE 
    CASE 
        WHEN DAYOFWEEK(NOW()) = 1
        THEN h.day_of_week = 7
    ELSE
        h.day_of_week = DAYOFWEEK(NOW() - 1) 
    END 
END 
AND s.id = '2'
LIMIT 0 , 30

Here is some data from the rest_opening_hours table:

INSERT INTO `rest_opening_hours` (`restid`, `day_of_week`, `hours_open`, `hours_close`) VALUES
(2, 1, '17:00:00', '23:00:00'),
(2, 7, '17:00:00', '06:00:00'),
(2, 6, '17:00:00', '00:00:00'),
(2, 5, '17:00:00', '01:00:00'),
(2, 4, '17:00:00', '02:00:00'),
(2, 3, '03:00:00', '23:00:00'),
(2, 2, '17:00:00', '04:00:00');

My only problem is, that my query is returning multiple records, and I don’t really see why. The query returns (on a Sunday – day 1) the results for Sunday (day 1) and also for Saturday (day 7) not just day 7 as I had intended in my query!?

I would expect the result “06:00” to be returned, as today it is Sunday (day 1) and following the logic, when DAYOFWEEK(NOW()) = 1 then we select where h.days_of_week = 7 (ie, Yesterday’s opening hours) as we previously deduced that h.hours_close < h.hours_open. However, I am getting two results: “06:00” and “23:00” which makes no sense to me, it’s almost as if MySQL is ignoring the second case and just returning both!??!?!

Can anyone shed any light on this, as I have spent ages playing around with this and I don’t seem to be getting anywhere.

Thanks in advance!

Ryan

Amended Query

SELECT h.hours_close
FROM restaurants s
INNER JOIN rest_opening_hours h ON s.id = h.restid
WHERE 
CASE 
    WHEN h.hours_close > h.hours_open
    THEN h.day_of_week = DAYOFWEEK( NOW( ) ) 
    ELSE h.day_of_week = DAYOFWEEK( DATE_SUB( NOW( ) , INTERVAL 1 DAY ) ) 
END 
AND s.id =  '2'

It appears that my issue is that my query is selecting both the day before (7) and the day in question (1) because one is h.hours_close > h.hours_open and the other is h.hours_close < h.hours_open – any ides on how I could isolate this to just one result, perhaps a restructure of sorts so that I am only looking at the one for the day before IF the closing time is less than the opening time (that is, it closes the next day).

In Pseudo-code:

if (closingtime < openingtime) {
return closing time from yesterday
} else {
return closing time from today
}

it is so simple – why is it causing me so many damn problems!?!?!?

Answer 1

God bless pseudo code. That was all I needed 🙂 This is what you want:

select * from t1
join (
  select restid, day_of_week,
    if(hours_close < hours_open,
      if(day_of_week = 1, 7, day_of_week - 1),
      day_of_week
    ) as NewDayOfWeek
  from t1
) as S
on s.restid = t1.restid and s.day_of_week = t1.day_of_week