EAV on postgres using jsonb - sql

Question

I'm trying to implement EAV pattern using Attribute->Value tables but unlike standard way values stored in jsonb filed like {"attrId":[values]}. It's help make easy search request like:
SELECT * FROM products p WHERE p.attributes #> "{1:[2]} AND p.attributes #> "{1:[4]}"
Now I'm wondering is it will be a good approach, and what is a effective way to calculate count of available variations, for example:
-p1- {"width":[1]}
-p2- {"width":[2],"height":[3]}
-p3- {"width":[1]}
Output will
width: 1 (count 2); 2 (count 1)
height: 3 (count 1)
when select width 2
width: 1 (count 0); 2 (count 1)
height: 3 (count 1)

Answer 1

"Flat is better than nested" -- the zen of python
I think you would be better served to use simple key/value pairs and in the rare event you have a complex value, then make it a list. But I don't see that use case.
Here is an example which answers your question. It could be modified to use your structure, but let's keep it simple:
First create a table and insert some JSON:
# create table foo (a jsonb);
# insert into foo values ('{"a":"1", "b":"2"}');
# insert into foo values ('{"c":"3", "d":"4"}');
# insert into foo values ('{"e":"5", "a":"6"}');
Here are the records:
# select * from foo;
a
----------------------
{"a": "1", "b": "2"}
{"c": "3", "d": "4"}
{"a": "6", "e": "5"}
(3 rows)
Here is the output of the json_each_text() function from https://www.postgresql.org/docs/9.6/static/functions-json.html
# select jsonb_each_text(a) from foo;
jsonb_each_text
-----------------
(a,1)
(b,2)
(c,3)
(d,4)
(a,6)
(e,5)
(6 rows)
Now we need to put it in a table expression to be able to get access to the individual fields:
# with t1 as (select jsonb_each_text(a) as rec from foo)
select (rec).key, (rec).value from t1;
key | value
-----+-------
a | 1
b | 2
c | 3
d | 4
a | 6
e | 5
(6 rows)
And lastly here is a grouping with the SUM function. Notice the a key which was in the database 2x, has been properly summed.
# with t1 as (select jsonb_each_text(a) as rec from foo)
select (rec).key, sum((rec).value::int) from t1 group by (rec).key;
key | sum
-----+-----
c | 3
b | 2
a | 7
e | 5
d | 4
(5 rows)
As a final note, (rec) has parentheses around it because otherwise it is incorrectly looked at as a table and will result in this error:
ERROR: missing FROM-clause entry for table "rec"