How to create index on json field in Postgres 9.3

问题:

In PostgreSQL 9.3 Beta 2 (?), how do I create an index on a JSON field? I tried it using the -> operator used for hstore but got the following error:

 CREATE TABLE publishers(id INT, info JSON);
 CREATE INDEX ON publishers((info->'name'));

ERROR: data type json has no default operator class for access method "btree" HINT: You must specify an operator class for the index or define a default operator class for the data type.

回答1:

Found:

CREATE TABLE publishers(id INT, info JSON); 
CREATE INDEX ON publishers((info->>'name'));