Question

Normaly if mysql or mssql i would do like below
Database A : test1
Database B : test2
Database C : test3

Sql Statement :

select * FROM test1.table1  
join test2  on test1.table1.id  = test2.table2.id
join test3  on test1.table1.id  = test3.table4.id 

How it work in Oracle and Php ?

Answer 1

Ok, you need to create a database link in oracle at first:

CREATE DATABASE LINK dblink_name 
   CONNECT TO username IDENTIFIED BY password
   USING 'service_name';

Service_name is a record in your database’s tnsnames.ora.

Or, if you don’t want to use tnsnames.ora, you can specify your net name right in create function, like this:

CREATE DATABASE LINK dblink_name 
     CONNECT TO username IDENTIFIED BY password
     USING '(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=hostname)(PORT=1521))(CONNECT_DATA(SID=dbname))';

and then use it this way:

SELECT host_name, instance_nmame FROM v$instance@dblink_name;