Question

Essentially I have some user generated meta data for individual items. Meta data consists of a title and a corresponding value. One item may have one particular metadata title while another may not. So, creating a new collumn in my main table seems like the wrong approach, since I don’t want every item to have the same meta data titles.

The problem is when I want to sort by that meta data. I can easily generate a table that makes the metadata look like just another collumn, but I want to sort by that to. So, to illustrate what I have:

Say I have the following tables:

Items Table:
id | color
----------
0  | red
1  | pink
2  | orange

MetaData Table
itemId |     title     |     data
-----------------------------------------
   0        shape           round
   1   |    shape      |    square
   0   |    sound      |    LOUD!

I can easily write the SQL and code to generate something like the following from those tables:

id  |    color   |   shape    |   sound
--------------------------------------------
0   |    red     |   round    |   LOUD!
1   |    pink    |   square   |            
2   |   orange   |            |   

So, when generating that, if a item doesn’t have a metadata title I’m displaying, then it’s just left blank. I would like to allow the user to sort by shape or sound and just have the ones that are blank show up at the bottom.

I could bring in all the data, generate the tables, then sort it in code..but…that wouldn’t be practical at all for hundreds of entries that I may need to work with.

Is this possible to do in SQL (I’m using mysql, but something more generic would be better in case I change that)? Is my table layout just impractical for this/should I do it a different way (I’d prefer not to change my table layout).

Thanks!

Answer 1

You can put the blank values at the bottom with something like this:

select
  Items.id,
  Items.color,
  max(case when title = 'shape' then data else null end) as shape,
  max(case when title = 'sound' then data else null end) as sound
from Items left outer join MetaData
on Items.id = MetaData.itemId
group by Items.id, Items.color
order by
  case when shape is not null then 0 else 1 end,
  shape