sqljsonpostgresqlpostgresql-9.2postgresql-9.3

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

I am looking for some docs and/or examples for the new JSON functions in PostgreSQL 9.2.

Specifically, given a series of JSON records:

[
  {name: "Toby", occupation: "Software Engineer"},
  {name: "Zaphod", occupation: "Galactic President"}
]

How would I write the SQL to find a record by name?

In vanilla SQL:

SELECT * from json_data WHERE "name" = "Toby"

The official dev manual is quite sparse:

Update I

I've put together a gist detailing what is currently possible with PostgreSQL 9.2. Using some custom functions, it is possible to do things like:

SELECT id, json_string(data,'name') FROM things
WHERE json_string(data,'name') LIKE 'G%';

Update II

I've now moved my JSON functions into their own project:

PostSQL - a set of functions for transforming PostgreSQL and PL/v8 into a totally awesome JSON document store

Solution

  • Postgres 9.2

    I quote Andrew Dunstan on the pgsql-hackers list:

    At some stage there will possibly be some json-processing (as opposed to json-producing) functions, but not in 9.2.

    Doesn't prevent him from providing an example implementation in PLV8 that should solve your problem. (Link is dead now, see modern PLV8 instead.)

    Postgres 9.3

    Offers an arsenal of new functions and operators to add "json-processing".

    The answer to the original question in Postgres 9.3:

    For a given table:

    CREATE TABLE json_tbl (data json);

    Query:

    SELECT object
FROM   json_tbl
     , json_array_elements(data) AS object
WHERE  object->>'name' = 'Toby';

    Advanced example:

    For bigger tables you may want to add an expression index to increase performance:

    Postgres 9.4

    Adds jsonb (b for "binary", values are stored as native Postgres types) and yet more functionality for both types. In addition to expression indexes mentioned above, jsonb also supports GIN, btree and hash indexes, GIN being the most potent of these.

    The manual goes as far as suggesting:

    In general, most applications should prefer to store JSON data as jsonb, unless there are quite specialized needs, such as legacy assumptions about ordering of object keys.

    Bold emphasis mine.
    Also, performance benefits from general improvements to GIN indexes.

    Postgres 9.5

    Complete jsonb functions and operators. Add more functions to manipulate jsonb in place and for display.

    Functionality and performance has been improved with every major Postgres version since. It's pretty complete by now (as of Postgres 16). One major, notable addition in ...

    Postgres 12

    ... is the SQL/JSON path language along with operators and functions. The answer to the example in the question can now be, for a given table (with jsonb):

    CREATE TABLE jsonb_tbl (data jsonb);

SELECT jsonb_path_query_first(data, '$[*] ? (@.name == "Toby")') AS object
FROM   jsonb_tbl
WHERE  data @> '[{"name": "Toby"}]';  -- optional, for index support

    Or equivalent:

    ...
WHERE  data @@ '$[*].name == "Toby"';

    fiddle

    See:

    About indexing: