How to filter rows on nested values in a json column?

Question

Here is my table (simplified, only significant columns):

CREATE TABLE things (
  id serial primary key
, name varchar
, blueprint json default '{}'
);

And some sample data:

# select * from things;

 id |  name   |                                  blueprint
----+---------+-----------------------------------------------------------------------------
  1 | Thing 1 | {}
  2 | Thing 2 | {"1":{"name":"Iskapola","wight":"2"}}
  3 | Thing 3 | {"1":{"name":"Azamund","weight":"3"}, "2":{"name":"Iskapola","weight":"1"}}
  4 | Thing 4 | {"1":{"name":"Ulamir","weight":"1"}, "2":{"name":"Azamund","weight":"1"}}

I'd like to select rows that have 'Azamund' anywhere under the name key. Something like this:

# select * from things where * ->> 'name' = 'Azamund';

 id |      blueprint
----+----------------------------------------------------------------------------
  7 | {"1":{"name":"Azamund","weight":"3"}, "2":{"name":"Iskapola","weight":"1"}}
  8 | {"1":{"name":"Ulamir","weight":"1"}, "2":{"name":"Azamund","weight":"1"}}

Data is nested exactly like in the sample (only one level).
Currently we are using PostgreSQL 9.3.5.

Is it possible in PostgreSQL 9.3? Maybe 9.4?

Answer 1

Your query is close. json_each() is the key function. Or jsonb_each() for jsonb. A couple of improvements:

SELECT *
FROM   things t
WHERE  EXISTS (
   SELECT FROM json_each(t.blueprint) b
   WHERE  b.value->>'name' ILIKE 'azamund'
   );

Old sqlfiddle
db<>fiddle here

• json_each() already returns the value as json data type. No need for an additional cast.

• Better, yet, use a LATERAL reference in EXISTS. This is much cleaner than unnesting with a set-returning function in the SELECT list. Related:

  • Call a set-returning function with an array argument multiple times

• Use ILIKE (~~*) for the pattern match. Regular expression matches (~, ~*) are more powerful, but also more expensive. So use the basic LIKE / ILKE where you can. Details:

  • Pattern matching with LIKE, SIMILAR TO or regular expressions in PostgreSQL

Alternative with JSON array

You have already seen my related answer for JSON arrays:

• How do I query using fields inside the new PostgreSQL JSON datatype?

While the query for nested JSON objects seems just as simple, there is superior index support for the array:

• Index for finding an element in a JSON array

---

May get simpler / more efficient with SQL/JSON in Postgres 12 ...