Question

I’ll try to explain it as simple as possible:

First some database structure with dummy data.

Structure

tb_spec_fk

feature     value
-----------------
1           1
1           2
1           3
1           4
1           5
2           2
2           3
3           1
3           4
4           2
4           3
4           4
5           1
5           3
5           5
6           3
6           5

tb_spec_feature

feature_id  filter
------------------
1           2
2           2
3           2
4           2
5           1
6           0

tb_spec_value

value_id    name
----------------
1           10
2           20
3           30
4           40
5           50

Now, what I want is the follow result

Result

feature_id  min_value   max_value
---------------------------------
1           10          50
2           20          30
3           10          40
4           20          40

But how?

Logic

Get from the tb_spec_feature where "filter" equals 2 the highest and lowest values which are present in the tb_spec_value table and connected together trough the tb_spec_fk table.

My attemps

A lot! But I’ll spare you 🙂

Answer 1

SELECT
    f.feature_id AS feature_id,
    MAX(value.name) AS max_value,
    MIN(value.name) AS min_value
FROM tb_spec_feature AS f
    JOIN tb_spec_fk AS fk ON f.feature_id=fk.feature
    JOIN tb_spec_value AS value ON fk.value=value.id
WHERE f.filter=2
GROUP BY f.feature_id

The two JOIN statements “link” the a feature to a value. GROUP BY groups all rows with the same feature id, and then you can take the min or max or any other aggregate function on those columns.

Demo