Select from a table from other schema

Question

Hi,
I want to make a select from a table how is into other Schema and into other instance.
form example, if I have _2 schemas (in diferent instances)_:
SCHEMA1 =
*(DESCRIPTION =*
*(ADDRESS =*
*(PROTOCOL = TCP)*
*(HOST = XXX.XXX.XXX.XX1)*
*(PORT = 1560)*
*(CONNECT_DATA =*
*(SERVER = DEDICATED)*
*(SERVICE_NAME = SCHEMA1)*
SCHEMA2 =
*(DESCRIPTION =*
*(ADDRESS =*
*(PROTOCOL = TCP)*
*(HOST = XXX.XXX.XXX.XX2)*
*(PORT = 1560)*
*(CONNECT_DATA =*
*(SERVER = DEDICATED)*
*(SERVICE_NAME = SCHEMA2)*
and into SCHEMA2 there is a table TABLE_A.
If I`m connected into SCHEMA1:
how can I do to make a select from the TABLE_A?
thanks very much.

Answer 1

1) Referring to an entry in the tnsnames.ora file as a "schema" as you have here with schema1 and schema2 is likely to be confusing. You have multiple schemas in the same database-- in this case, you appear to be trying to query tables in a different database. If we try to answer using your TNS aliases "schema1" and "schema2", there is likely to be a great deal of confusion between schemas/ databases/ and TNS aliases. So I will assume that your tnsnames.ora file actually reads
TNS_ALIAS1 =
  (DESCRIPTION =
    (ADDRESS =
      (PROTOCOL = TCP)
      (HOST = HOST1)
      (PORT = 1560)
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = DB1)
TNS_ALIAS2 =
  (DESCRIPTION =
    (ADDRESS =
      (PROTOCOL = TCP)
      (HOST = HOST2)
      (PORT = 1560)
  (CONNECT_DATA =
    (SERVER = DEDICATED)
    (SERVICE_NAME = DB2)
)2) Given the TNS aliases above, assuming that we are talking about the tnsnames.ora file on HOST1, you would need to create a database link from DB1 to DB2. You can either specify a fixed username and password for the database link or you can specify that the connection happens as the current user (which assumes that the passwords are synchronized between the databases).
CREATE DATABASE LINK to_db2
  CONNECT TO username_on_db2
  IDENTIFIED BY password_on_db2
  USING 'TNS_ALIAS2'3) Assuming the database link is in place
SELECT *
  FROM schema2.table_name@to_db2Justin