How to sum nested values from a JSON array based on conditions

Question

I have a table with 3 columns in Postgres 14.2: name, name_adds, aditional.

And these rules:

1. name and name_adds can be filled with the same value or not. Example: name (john) and name_adds (doe) or both value is (john)

2. column additional has one of two formats:

   format 1:

   {"default":[{"value_1": 100, "value_2": 0.1},{"value_1": 200, "value_2": 0.2}], "non_default":[{"value_1": 200, "value_2": 0.1}, {"value_1": 400, "value_2": 0.1}]}

   format 2:

   [{"value_1": 10,"value_2": 11},{"value_1": 1,"value_2": 19}

3. If (name = name_adds) sum default -> value_1

4. If (name != name_adds) sum non_default -> value_1

How can I sum format 1 or 2 from point 2. based on the rules in point 3. and 4.?

Example table:

name name_adds additional
---------------------------------------------------------------
john john {"default":[{"value_1": 100, "value_2": 0.1}, 
 {"value_1": 200, "value_2": 0.2}],"non_default": 
 [{"value_1": 200, "value_2": 0.1}, {"value_1": 400, 
 "value_2": 0.1}]}
john doe {"default":[{"value_1": 100, "value_2": 0.1}, 
 {"value_1": 200, "value_2": 0.2}],"non_default": 
 [{"value_1": 200, "value_2": 0.1}, {"value_1": 400, 
 "value_2": 0.1}]}
downy downy [{"value_1": 10, "value_2": 11},{"value_1": 1,"value_2": 19}]
downy dan [{"value_1": 10, "value_2": 11},{"value_1": 1,"value_2": 19}]

Expected result:

name name_adds sum_result
---------------------------------------------------------------
john john 300
john doe 600
downy downy 11
downy dan 11

I tried a query in this online demo, but didn't manage to get the expected result.

Answer 1

SELECT a.name, a.name_adds, sub.*
FROM test_json a
CROSS JOIN LATERAL (
 SELECT sum((obj ->> 'value_1')::int) AS sum_result -- or numeric?
 FROM json_array_elements(COALESCE(CASE WHEN name = name_adds
 THEN additional::json -> 'default'
 ELSE additional::json -> 'non_default' END
 , additional::json)) obj
 ) sub;

db<>fiddle here

This relies on additional::json -> 'default' (or 'non_default', respectively) being NULL in case of "format 2", in which case we take additional::json directly for "format 1" using COALESCE.
Then unnest with json_array_elements(), and sum extracted value_1.

The column additional should be type json (or jsonb) to begin with.

Chances are, you would be much better off with a normalized relational design replacing that highly regular JSON column completely.

• wuku: cool it's work, you are right about additional type, I will change it. Thanks a lot