Question

I have this database structure:

sites
id | name
1  | Site 1
2  | Site 2

locations
id | city
23 | Baltimore
24 | Annapolis

people
id | name
45 | John
46 | Sue

sites_meta
id | site_id | meta_name | meta_value
1  |    1    |   local   |     23
2  |    1    |   person  |     45
3  |    2    |   local   |     24
4  |    2    |   person  |     46

So, as you can see, Site 1 (id 1) is in Baltimore and is associated with John, Site 2 (id 2) is in Annapolis and associated with Sue.

I need to figure out a clever sql statement that can return

id |   name   | id |    city    | id | name
 1 |  Site 1  | 23 |  Baltimore | 45 | John
 2 |  Site 2  | 24 |  Annapolis | 46 | Sue

I would be super appreciative if anyone can help me out. I’ve tried a few combinations of a select statement, but I keep getting stuck with using two values from the sites_meta table.

Answer 1

select
    s.id as siteId,
    s.name as siteName,
    max(l.id) as locationId,
    max(l.city) as city,
    max(p.id) as personId,
    max(p.name) as personName
from
    sites_meta sm
    join sites s on s.id = sm.site_id
    left join locations l on l.id = sm.meta_value and sm.meta_name = 'local'
    left join people p on p.id = sm.meta_value and sm.meta_name = 'person'
group by
    s.id,
    s.name

You can probably imagine how this kind of “meta” table might become a pain… especially as more items are added to it.

Instead, you might consider replacing it with two new tables, sites_locations and sites_people.