⟩ What Privilege Is Needed for a User to Query Tables in Another Schema?
For a user to run queries (SELECT statements) on tables of someone else's schema, he/she needs the SELECT ANY TABLE privilege. The following tutorial exercise gives you a good example of granting "dev" to query tables in "hr" schema:
>.insqlplus /nolog
SQL> CONNECT DEV/developer
SQL> SELECT COUNT(*) FROM hr.employees;
ORA-01031: insufficient privileges
SQL> disconnect
SQL> connect SYSTEM/globalguideline
SQL> GRANT SELECT ANY TABLE TO dev;
Grant succeeded.
SQL> disconnect
SQL> CONNECT DEV/developer
SQL> SELECT COUNT(*) FROM hr.employees;
COUNT(*)
----------
107
As you can see, "dev" can query tables in any schema now.
You also need to remember that table name must be prefixed with the schema name (same as owner user name).