Question

In my application there are products and a product-variant-group which has a defined set of properties which a product of this group must declare and the combination of the properties is unique across that product-variant-group.

Example screen from amazon:

In the image the first select menu has all values obviously. The next select menu depends on the previously selected value, and so on.

Those defined group properties have a unique priority assigned to it which in the following derived table equals the property itself.

For a given property/priority and given list of of property/priority-value pairs. I want to retrieve its possible values.
The priorities of the value pairs must be smaller then the given priority.

public String[] getProductVariantGroupValues(int productVariantGroupId, int priority, Map<Integer, String> prevValues);

An example makes it much clearer:

I have an sql statement which lists all product-variant-group properties that related products have defined:

+---------+----------+-------- +
| product | priority | value   |
+---------+----------+---------+
|       1 |        1 | Black   |
|       1 |        2 | 38      |
|       1 |        3 | Dots    |
|       2 |        1 | Black   |
|       2 |        2 | 38      |
|       2 |        3 | Stripes |
|       3 |        1 | Yellow  |
|       3 |        2 | 40      |
|       3 |        3 | Stripes |
+---------+----------+---------+

Other view for understanding *(priority is arbitrary just for understanding, with this view this would be trivial)*:

+---------+--------+--------+---------+
| product | value1 | value2 | value3  |
+---------+--------+--------+---------+
|       1 | Black  | 38     | Dots    |
|       2 | Black  | 38     | Stripes |
|       3 | Yellow | 40     | Stripes |
+---------+---------------------------+

Call the above method with priority = 3 and prevValues = {(1, Black), (2, 38)} should result in following result array: {Dots, Stripes}.

If black is selected for property/priority 1 and 38 is selected for property/priority 2 the only possible following values for property/priority 3 are {Dots, Stripes}

The example is simplified and an arbitrary number of properties/priority should be supported. The query must be created dynamically to support arbitrary number of lower priority values.

Maybe I should just use the second table appraoch with a fixed set of properties which would make the unique constraint and this query very simple.

Answer 1

If I understand the question correctly, you have a value for priority 1 and for priority 2 and want to get all priority 3 values that match. The following query gets the products:

select product
from t
group by product
having max(case when priority = 1 and value = 'Black' then 1 else 0 end) = 1 and
       max(case when priority = 2 and value = 40 then 1 else 0 end) = 1

To get the priority 3 values requires or a clever select statement (assuming priorities are not repeated for a product):

select product, max(case when priority = 3 then value end)
from t
group by product
having max(case when priority = 1 and value = 'Black' then 1 else 0 end) = 1 and
       max(case when priority = 2 and value = 40 then 1 else 0 end) = 1

These queries are to give you an idea of how to construct the queries in your code. The generalization should be pretty straightforward.