I am connected to a oracle database with a read only user and i used service name while Setting up connection in sql developer hence i dont know SID ( schema ).
How can
To create a read-only user, you have to setup a different user than the one owning the tables you want to access.
If you just create the user and grant SELECT permission to the read-only user, you'll need to prepend the schema name to each table name. To avoid this, you have basically two options:
ALTER SESSION SET CURRENT_SCHEMA=XYZ
CREATE SYNONYM READER_USER.TABLE1 FOR XYZ.TABLE1
So if you haven't been told the name of the owner schema, you basically have three options. The last one should always work:
SELECT SYS_CONTEXT('USERENV','CURRENT_SCHEMA') FROM DUAL
SELECT * FROM ALL_SYNONYMS WHERE OWNER = USER
SELECT * FROM ALL_TABLES WHERE OWNER NOT IN ('SYS', 'SYSTEM', 'CTXSYS', 'MDSYS');