How do I get result counts for custom fields using class inheritance table?

Question

I'm currently playing around with building a basic storefront app for learning purposes.

I have two tables in my MySQL database "items" and "field_values" with a 1 to many relationship. There is also a fields table and a field sets table but these are not relevant to the query. A set can contain many fields and an item has one or more sets of fields.

Items

id, name

Field Values

set_id, item_id, field_1, field_2, field_3 etc..

I've built a dynamic query that allows the end user to filter down results based on the values of these fields so when 2 fields are filtered I have a query like so (pseudo)

SELECT * FROM items LEFT JOIN field_values WHERE field_1=2 and field_2=7

My question is how would I expand this to show counts for the remaining options? In other words the query above gives me one resultset but then I would also like to get the count for each of the field_3, field_4 etc values so the user knows in advance how many results they will get and so I can not present any options that would return 0 results.

I hope that makes sense.

Thanks in advance

Andy

Answer 1

You would construct the where clause as you do now. Then do an aggregation query instead of fetching the columns:

SELECT field_1, field_2, field_3, count(*)
FROM items LEFT JOIN
     field_values
WHERE field_1 = 2 and field_2 = 7
GROUP BY field_1, field_2, field_3;

This will give all the combinations of the other values.