Postgresql – Postgres invalid input syntax for type json Detail: Token “%” is invalid

I'm trying to check if some text contains the concatenation of a text and a value from an array in Postgres, something like:

SELECT true from jsonb_array_elements('["a", "b"]'::jsonb) as ids 
WHERE 'bar/foo/item/b' LIKE '%item/' || ids->>'id' || '%'
I'm getting the following error:
ERROR: invalid input syntax for type json Detail: Token "%" is invalid. Position: 95 Where: JSON data, line 1: %...
How can I make use of the values of the array, concatenate them with the text and check the LIKE expression?
I have tried several ideas of explicitly adding a cast like ::jsonb, but no luck so far. 
The problem is that the || and ->> operators have the same precedence and are left associative, so the expression is interpreted as
(('%item/' || ids) ->>'id') || '%'
You'd have to add parentheses:
'%item/' || (ids->>'id') || '%'
Related Solutions
Postgresql – ‘password authentication failed for user “postgres”‘

If I remember correctly the user postgres has no DB password set on Ubuntu by default. That means, that you can login to that account only by using the postgres OS user account.
Assuming, that you have root access on the box you can do:
sudo -u postgres psql
If that fails with a database "postgres" does not exists error, then you are most likely not on a Ubuntu or Debian server :-) In this case simply add template1 to the command:
sudo -u postgres psql template1
If any of those commands fail with an error psql: FATAL:  password authentication failed for user "postgres" then check the file /etc/postgresql/8.4/main/pg_hba.conf: There must be a line like this as the first non-comment line:
local   all         postgres                          ident
For newer versions of PostgreSQL ident actually might be peer. That's OK also.
Inside the psql shell you can give the DB user postgres a password: 
ALTER USER postgres PASSWORD 'newPassword';
You can leave the psql shell by typing CtrlD or with the command \q.
Now you should be able to give pgAdmin a valid password for the DB superuser and it will be happy too. :-)
    
Ruby-on-rails – Getting error: Peer authentication failed for user “postgres”, when trying to get pgsql working with rails

The problem is still your pg_hba.conf file*.
This line:
local   all             postgres                                peer
Should be:
local   all             postgres                                md5
* The location of this file isn't very consistent. The command locate pg_hba.conf should help; here's some examples: /etc/postgresql/*/main/pg_hba.conf and /var/lib/pgsql/data/pg_hba.conf.
After altering this file, don't forget to restart your PostgreSQL server. If you're on Linux, that would be sudo service postgresql restart.
These are brief descriptions of both options according to the official PostgreSQL docs on authentication methods.
Peer authentication
The peer authentication method works by obtaining the client's
operating system user name from the kernel and using it as the allowed
database user name (with optional user name mapping). This method is
only supported on local connections.
Password authentication
The password-based authentication methods are md5 and password. These
methods operate similarly except for the way that the password is sent
across the connection, namely MD5-hashed and clear-text respectively.
If you are at all concerned about password "sniffing" attacks then md5
is preferred. Plain password should always be avoided if possible.
However, md5 cannot be used with the db_user_namespace feature. If the
connection is protected by SSL encryption then password can be used
safely (though SSL certificate authentication might be a better choice
if one is depending on using SSL).
Sample location for pg_hba.conf:

/etc/postgresql/9.1/main/pg_hba.conf