Ordering query result by field from a different table (MySQL)

Question

I have a MySQL table structure and need to get a specific query working but I just can\'t wrap my head around it somehow. First off, here\'s the relevant table structure.

<

Answer 1

If I understand correctly, you would use join:

select f.*
from folders f join
     werte w
     on w.folder_id = f.id
where w.number = 2 
order by f.approved, str_to_date(werte, '%d.%m.%Y');

As a note: if you are doing to store dates in strings, then use the ISO standard format YYYY-MM-DD. If you used this format, the str_to_date() would be unnecessary, because an alphabetic ordering of the string representation would be correct.

Also, if there might not be a match in the werte table, then you should use left join instead of inner join. The above assumes there is a match (or you only want rows that have a date).

Answer 2

If you would like to avoid duplicates, you can use group by on the date:

SELECT f.id, STR_TO_DATE(w.werte, '%d.%m.%Y') as d 
 FROM folders f JOIN werte w
 ON w.folder_id = f.id
 GROUP BY d
 ORDER BY d;