Add a row-level access policy with VPD (DBMS_RLS)

Command

-- 1) Policy function returning the predicate:
CREATE OR REPLACE FUNCTION customer_app.customer_vpd_fn (
  p_schema IN VARCHAR2,
  p_object IN VARCHAR2
) RETURN VARCHAR2
AS
BEGIN
  -- The schema owner sees all rows (NULL = no restriction)
  IF SYS_CONTEXT('USERENV', 'SESSION_USER') = 'CUSTOMER_APP' THEN
    RETURN NULL;
  END IF;
  -- Other users see only their own city
  RETURN 'city = SYS_CONTEXT(''USERENV'', ''CLIENT_IDENTIFIER'')';
END;
/

-- 2) Attach the policy to the table:
BEGIN
  DBMS_RLS.ADD_POLICY(
    object_schema   => 'CUSTOMER_APP',
    object_name     => 'CUSTOMER',
    policy_name     => 'CUSTOMER_CITY_VPD',
    function_schema => 'CUSTOMER_APP',
    policy_function => 'CUSTOMER_VPD_FN',
    statement_types => 'SELECT, UPDATE, DELETE',
    update_check    => TRUE,
    policy_type     => DBMS_RLS.CONTEXT_SENSITIVE);
END;
/

-- 3) Check:
SELECT object_owner, object_name, policy_name, function,
       sel, upd, del, chk_option, enable, policy_type
FROM   dba_policies WHERE object_owner = 'CUSTOMER_APP';
-- Test (as the application user): EXEC DBMS_SESSION.SET_IDENTIFIER('Ankara');

-- 4) Temporarily disable / drop:
EXEC DBMS_RLS.ENABLE_POLICY('CUSTOMER_APP', 'CUSTOMER', 'CUSTOMER_CITY_VPD', FALSE);
EXEC DBMS_RLS.DROP_POLICY('CUSTOMER_APP', 'CUSTOMER', 'CUSTOMER_CITY_VPD');

What it does

Virtual Private Database automatically appends the WHERE predicate returned by the policy function to every SQL against the table, so users of the same table see/modify only the rows they are entitled to. update_check=>TRUE prevents a user from updating a row to a value they could not see.

When to use it

In multi-tenant applications, for region/branch-based data isolation, and to add row security without touching application code.

Caution

Included in Enterprise Edition, no extra license. CLIENT_IDENTIFIER can be set freely by the client; in production use an application context set by a trusted package (CREATE CONTEXT ... USING). SYS and users with EXEMPT ACCESS POLICY bypass the policy; Data Pump exports without that privilege silently export partial data. An error in the function blocks all access with ORA-28112. A wrong policy_type (e.g. STATIC) caches the predicate and returns wrong results.