I have an Apex page which selects databases from drop down:

All
DBDEV
DBTEST
POCTEST
The IG Query currently is:

  select db_name, description,enable,allow , 
(select database_link from links a where a.db_name = b.db_name) link_db from db_details b; 

DB_DETAILS table data in local database.

DB_NAME DESCRIPTION ENABLE ALLOW
DBDEV DATA 1 Y Yes
DBTEST DATA 2 Y Yes
POCTEST DATA 3 Y Yes
DBDEV DATA 4 Y Yes
DBTEST DATA 5 Y Yes

LINKS TABLE DATA:

DB_LINK DATABASE
DDEV DBDEV
DTEST DBTEST
PTEST POCTEST

In this query i need to add a column that compares the table db_details with db_details table in different databases.

Ex: DB_DETAILS and DB_DETAILS@DBDEV have same table structure and same 4 columns: db_name, description,enable,allow
So, there has to be column by column comparison and the difference needs to be reflected in the field in form of count or a colour indication.
This field should be a link and that should then open a pop-up showing the rows from both tables, i.e. local and the database.

How can this be achieved in apex?

DECLARE

  l_query varchar2(200) := 'SELECT * FROM DB_DETAILS@'||:P1_DB_LINK;
begin
    IF APEX_COLLECTION.COLLECTION_EXISTS (p_collection_name => 'MYDATA') THEN
            APEX_COLLECTION.DELETE_COLLECTION (p_collection_name => 'MYDATA');
    end if;

    APEX_COLLECTION.CREATE_COLLECTION_FROM_QUERY (
        p_collection_name => 'MYDATA', 
        p_query => l_query,
        p_generate_md5 => 'YES');

End;

select 
    seq_id link_item,
    seq_id ID,
    c001 mycol1, 
    c002 mycol2,
    c003 mycol3,
    ...
from apex_collections
where collection_name = 'MYDATA';