compare values with JSON_EXTRACT

Question

I've got a strange issue when I try to compare values with JSON_EXTRACT.

Here is an extract of my column opening_hours in database:

{"1": {"end": {"max_hour": "1290", "min_hour": "840"}, "begin": {"max_hour": "720", "min_hour": "420"}}, 
 "2": {"end": {"max_hour": "1290", "min_hour": "840"}, "begin": {"max_hour": "720", "min_hour": "420"}}, 
 "3": {"end": {"max_hour": "1290", "min_hour": "840"}, "begin": {"max_hour": "720", "min_hour": "420"}}, 
 "4": {"end": {"max_hour": "1290", "min_hour": "840"}, "begin": {"max_hour": "720", "min_hour": "420"}}, 
 "5": {"end": {"max_hour": "1290", "min_hour": "840"}, "begin": {"max_hour": "720", "min_hour": "420"}}}

When I search if, for example, "720" is between the min_hour and max_hour of each part of the day (begin and end), I've got results:

SELECT *
FROM `service_provider`
WHERE ((JSON_EXTRACT(`opening_hours`, '$."3"."begin"."min_hour"') <= '720' 
        AND '720' <= JSON_EXTRACT(`opening_hours`, '$."3"."begin"."max_hour"')) 
      OR (JSON_EXTRACT(`opening_hours`, '$."3"."end"."min_hour"') <= '720' 
          AND '720' <= JSON_EXTRACT(`opening_hours`, '$."3"."end"."max_hour"')));

====> GOT SOME RESULTS !

But when I do the same thing with "1200", no result found:

SELECT *
FROM `service_provider`
WHERE ((JSON_EXTRACT(`opening_hours`, '$."3"."begin"."min_hour"') <= '1200' 
         AND '1200' <= JSON_EXTRACT(`opening_hours`, '$."3"."begin"."max_hour"')) 
      OR (JSON_EXTRACT(`opening_hours`, '$."3"."end"."min_hour"') <= '1200' 
           AND '1200' <= JSON_EXTRACT(`opening_hours`, '$."3"."end"."max_hour"')));

-----> NO RESULTS.

Yet it is well between "840" and "1290".

I noticed that only numbers before or equal at "720" gave results, so it doesn't take into account the second part of my query (after the OR). Why? Thank you.

Answer 1

The first thought I had was, are those JSON_EXTRACT final values returned as integer or string? And from my testing, it's returning string. So, when you do comparison using "<=" on string, it won't behave like numbers. Let's see your first query:

SELECT *
FROM `service_provider`
WHERE ((JSON_EXTRACT(`opening_hours`, '$."3"."begin"."min_hour"') <= '720' 
        AND '720' <= JSON_EXTRACT(`opening_hours`, '$."3"."begin"."max_hour"')) 
      OR (JSON_EXTRACT(`opening_hours`, '$."3"."end"."min_hour"') <= '720' 
          AND '720' <= JSON_EXTRACT(`opening_hours`, '$."3"."end"."max_hour"')));

This return result because you're using OR and the first condition of

(JSON_EXTRACT(`opening_hours`, '$."3"."begin"."min_hour"') <= '720' 
        AND '720' <= JSON_EXTRACT(`opening_hours`, '$."3"."begin"."max_hour"')

is true because of {"max_hour": "720", "min_hour": "420"} are both equal or smaller than 720 . Well, more like "7" is bigger than "4" or similar to "7". What if you remove the first condition in OR like:

SELECT *
FROM `service_provider`
WHERE (JSON_EXTRACT(`opening_hours`, '$."3"."end"."min_hour"') <= '720' 
          AND '720' <= JSON_EXTRACT(`opening_hours`, '$."3"."end"."max_hour"'));

This won't return you anything since in the first comparison, "end"."min_hour" returned 840 hence "8" is bigger than "7" AND the second condition "end"."max_hour" value of 1290 being recognize as smaller because "1" is smaller than "7".

I think you got the idea. Since this is comparing string, it's always the first character in the value that being compared first.

A quick workaround to your current issue is to turn the JSON_EXTRACT value as integer. My suggestion:

SELECT *
FROM `service_provider`
WHERE ((JSON_EXTRACT(`opening_hours`, '$."3"."begin"."min_hour"')+0 <= 1200
         AND 1200 <= JSON_EXTRACT(`opening_hours`, '$."3"."begin"."max_hour"')+0) 
      OR (JSON_EXTRACT(`opening_hours`, '$."3"."end"."min_hour"')+0 <= 1200 
           AND 1200 <= JSON_EXTRACT(`opening_hours`, '$."3"."end"."max_hour"')+0));

Adding +0 at the end of the JSON_EXTRACT value will quickly turn the string to integer and you might as well just remove ' from '1200' .

If you want to look at the values returned from JSON extract and use it, you can move all of them into SELECT and use HAVING to do comparison like:

SELECT JSON_EXTRACT(`opening_hours`, '$."3"."begin"."min_hour"')+0 bmin,
       JSON_EXTRACT(`opening_hours`, '$."3"."begin"."max_hour"')+0 bmax,
       JSON_EXTRACT(`opening_hours`, '$."3"."end"."min_hour"')+0 emin,
       JSON_EXTRACT(`opening_hours`, '$."3"."end"."max_hour"')+0 emax
FROM `service_provider`
HAVING ((bmin <= 1200 and  1200 <= bmax) or (emin <= 1200 and 1200 <= emax))

Here is a fiddle of my tests