I have Postgres JSONB array of objects, looking like this :
'[
{
"skillId": "1",
"skillLevel": 42
},
{
"skillId": "2",
"skillLevel": 41
}
]'
This JSONB is a function argument.
What is the most efficient way to retrieve skillLevel for skillId = "1".
I've tried to play with jsonb_array_elements but everything I've done so far is looking really messy.
In Postgres 9.4+ use the function jsonb_array_elements() in a lateral join:
select (elem->>'skillLevel')::int as skill_level
from my_table
cross join jsonb_array_elements(json_col) elem
where elem->>'skillId' = '1';
You can implement the idea in a simple function, e.g:
create or replace function extract_skill_level(json_data jsonb, id int)
returns integer language sql as $$
select (elem->>'skillLevel')::int
from jsonb_array_elements(json_data) elem
where elem->>'skillId' = id::text
$$;
select extract_skill_level(json_col, 1) as skill_level
from my_table;
In Postgres 12+ you have a nice alternative in the form of jsonb path functions:
select (
jsonb_path_query(
json_col,
'$[*] ? (@.skillId == "1")'
)->'skillLevel'
)::int as skill_level
from my_table;
Read more about JSON Functions and Operators.
