return count 0 with mysql group by

Question

database table like this

============================
= suburb_id   |   value
= 1           |    2
= 1           |    3
= 2           |    4
= 3           |          


        

Answer 1

@geofftnz's solution works great if all conditions are simple like in this case. But I just had to solve a similar problem to generate a report where each column in the report is a different query. When you need to combine results from several select statements, then something like this might work.

You may have to programmatically create this query. Using left joins allows the query to return rows even if there are no matches to suburb_id with a given id. If your db supports it (which most do), you can use IFNULL to replace null with 0:

select IFNULL(a.count,0), IFNULL(b.count,0), IFNULL(c.count,0), IFNULL(d.count,0)
from (select count(suburb_id) as count from suburbs where id=1 group by suburb_id) a,
 left join (select count(suburb_id) as count from suburbs where id=2 group by suburb_id) b on a.suburb_id=b.suburb_id
 left join (select count(suburb_id) as count from suburbs where id=3 group by suburb_id) c on a.suburb_id=c.suburb_id
 left join (select count(suburb_id) as count from suburbs where id=4 group by suburb_id) d on a.suburb_id=d.suburb_id;

The nice thing about this is that (if needed) each "left join" can use slightly different (possibly fairly complex) query.

Disclaimer: for large data sets, this type of query might have not perform very well (I don't write enough sql to know without investigating further), but at least it should give useful results ;-)