Query for element of array in JSON column

问题:

Recently upgraded to using PostgreSQL 9.3.1 to leverage the JSONfunctionalities. In my table I have a json type column that has a structure like this:

{
   "id": "123",
   "name": "foo",
   "emails":[
      {
        "id": "123",
        "address": "somethinghere"
      },
      {
        "id": "456",
        "address": "soemthing"
      }
   ]
} 

This is just dummy data for the purpose of the question.

Is it possible to query for a specific item in the emails array based on the id?
Pretty much: "return email where id=123)"?

回答1:

Yes, that's possible:

SELECT *
FROM   tbl t, json_array_elements(t.json_col->'emails') AS elem
WHERE  elem->>'id' = 123;

tbl being your table name, json_col being the name of the JSON column.

More details in this related answer:

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

More about the implicit CROSS JOIN LATERAL in the last paragraph of this related answer:

• PostgreSQL unnest() with element number

Index to support this kind of query:

• Index for finding an element in a JSON array

回答2:

With a JSONB column in Postgres 9.4+ you can use the contains operator @> to query for an element in an array:

SELECT * FROM jsontest WHERE data @> '{ "emails": [{ "id": "123" }] }';

See Query for array elements inside JSON type for more details.

Here is a working example:

CREATE TABLE jsontest(data JSONB NOT NULL);
INSERT INTO jsontest VALUES (
  '{
     "name": "foo",
     "id": "123",
     "emails": 
     [
       {
         "address": "somethinghere",
         "id": "123"
       },
       {
         "address": "soemthing",
         "id": "456"
       }
     ]
  }'
);
SELECT * FROM jsontest WHERE data @> '{ "emails": [{ "id": "123" }] }';

data
----
{"id": "123", "name": "foo", "emails": [{"id": "123", "address": "somethinghere"}, {"id": "456", "address": "soemthing"}]}

(1 row)

回答3:

Came across this post and found that you can directly query on table like this:

SELECT *
FROM   table_name, json_array_elements(json_column) AS data
WHERE  data->>'id' = 123;

Omitting this part:

json_array_elements(t.json_col->'emails')

回答4:

You can do it as simple as :

SELECT * FROM table WHERE emails->>'id' = '123';

it seems you store the id as string, if it was an integer you can do it like this :

SELECT *  from table WHERE cast(emails->>'id' as integer ) = 123  ;

or you can get all the rows with id > 10

SELECT *  from table WHERE cast(emails->>'id' as integer ) > 10  ;