Postgres Get all possible column combinations

Question

So I got a View of items in Postgres that looks like this:

id	brand_id	category_id	color_id	material_id	pattern_id	style_id
1	100	101	100	101	null	101
1	100	101	101	102	null	102
2	101	101	102	103	102	null
2	101	101	102	103	103	null
3	105	101	null	103	104	null
4	101	101	102	103	103	105

I need all DISTINCT possible combinations (excluding item_id) but forming groups that not always will include all columns.

Example of combinations for the First Row (but I need the same for all items without getting duplicated groups):

brand_id	category_id	color_id	material_id	pattern_id	style_id
100	null	null	null	null	null
null	101	null	null	null	null
null	null	100	null	null	null
null	null	null	101	null	null
null	null	null	null	null	101
100	101	null	null	null	null
100	null	100	null	null	null
100	null	null	101	null	null
100	null	null	101	null	null
100	null	null	101	null	101
100	101	100	null	null	null
100	101	null	101	null	null
100	101	null	null	null	101

I tried a CROSS JOIN with the original categories tables but I get a enormous table of combinations and also I don't get the groups of 1, 2, 3, 4 or 5 categories, I get the combinations including ALL six categories

Answer 1

You can use CUBE subclause for GROUP BY, which produces the following output for your first row:

---

    select 
100 brand_id,   101 category_id,    100 color_id,   
101 material_id,    null pattern_id,    101 style_id
    group by
    cube (brand_id, category_id,    color_id,   material_id ,pattern_id ,style_id);

brand_id	category_id	color_id	material_id	pattern_id	style_id
100		100	101		101
100			101		101
			101		101
			101
100		100
100	101	100	101
100		100	101
100		100	101
	101	100	101
	101	100	101
	101		101		101
	101	100	101		101
100	101	100
100	101	100	101
					101
100					101
100		100			101
		100			101
		100	101		101
100		100	101		101
	101				101
	101	100			101
	101	100	101		101
			101
			101		101
100	101	100	101		101
		100
		100			101
100	101	100			101
	101
	101				101
	101	100			101
		100	101
		100	101
		100	101		101
	101		101
	101		101
	101		101		101
100	101		101		101
	101	100
	101	100
100	101	100
100
100	101
100	101		101
100
100			101
100			101
100			101		101
					101
100					101
100	101				101
100	101				101
	101
100	101
100	101		101
100	101		101		101
100	101	100	101		101
		100
100		100
100		100			101
100	101	100			101

---

View on DB Fiddle