Question

I have this database query:

select      scheduled_hike_id 
        ,   hike_date 
        ,   hike_title 
        ,   hike_group_id 
        ,   hike_privacy 
        ,   hike_description 
        ,   DAYOFMONTH(hike_date) 
        ,   DAYNAME(hike_date) 
        ,   YEAR(hike_date) 
        ,   MONTH(hike_date) 
from        scheduled_hikes 
where       is_cancelled is null 
and         hike_date > DATE_ADD(NOW(), INTERVAL -1 DAY) 
and         show_on_home_page = 1  
order by    hike_date limit 4

It returns what I expected. When I add a clause “and hike_privacy != 3” it returns MUCH fewers results.

The other values in the column are NULL, 1, 2

Any ideas why the != 3 isn’t working as I expected? Also, <3 is giving similarly unexpected results. I am using MySQL

Answer 1

If hike_privacy is null, it won’t match hike_privacy != 3.

Try: and (hike_privacy != 3 or hike_privacy is null)

Nulls never match non “null style” comparisons.

Note: Make sure you use brackets around your “OR” terms! In SQL, OR takes precedence, so without the brackets it would parsed as if it was coded like this (note the position of the brackets):

where   (       is_cancelled is null 
            and hike_date > DATE_ADD(NOW(), INTERVAL -1 DAY) 
            and show_on_home_page = 1 
            and hike_privacy != 3
        ) 
or      hike_privacy is null

which is quite different from what we want, which is:

where       is_cancelled is null 
        and hike_date > DATE_ADD(NOW(), INTERVAL -1 DAY) 
        and show_on_home_page = 1 
        and (       
                    hike_privacy != 3 
                or hike_privacy is null
            )