Using variables as table names. Ideas for alternative designs

Question

Hi,
I am designing an application which uses synonyms to pull information from 'client' DBs via DB Links. The synonyms are created with a DB_ID in the name (example: CUSTOMER_100, CUSTOMER_200... where 100 and 200 are DB IDs from 2 separate client DBs.
I have a procedure which selects data from the synonym based on what DB_ID is passed to the procedure. I want to be able to run this one procedure for any DB_ID that is entered. I am now aware I cannot use variable names for table names and using EXECUTE IMMEDIATE doesnt seem to fit for what I am trying to do.
Does anybody have any suggestions or re-design options I could use to achieve this generic procedure that will select from a certain synonym based on the DB info input parameters? Thanks.
CREATE OR REPLACE PROCEDURE CUSTOMER_TEST(p_host IN VARCHAR2, p_db_name IN VARCHAR2, p_schema IN VARCHAR)
IS
   v_hostname     VARCHAR2 (50) := UPPER (p_host);
   v_instance     VARCHAR2 (50) := UPPER (p_db_name);
   v_schema     VARCHAR2 (50) := UPPER (p_schema);
   v_db_id  NUMBER;  
   v_synonym VARCHAR2(50);
   CURSOR insert_customer
   IS
     SELECT 
       c.customer_fname,
       c.customer_lname
     FROM v_synonym_name c;
BEGIN
-- GET DB_ID BASED ON INPUT PARAMETERS       
  select d.db_id
  into v_db_id
  from  t_mv_db_accounts ac,
  t_mv_db_instances i,
   t_mv_dbs d,
   t_mv_hosts h
  where ac.db_ID = d.db_ID
  and i.db_ID = d.db_ID
  and i.HOST_ID = h.host_id
  and upper(H.HOST_NAME) = v_hostname
  and upper(D.DB_NAME) = v_instance
  and upper(Ac.ACCOUNT_NAME) = v_schema;
  --APPEND DB_ID TO THE SYNOYNM NAME
  v_synonym := 'CUSTOMER_'||v_db_id;
  FOR cust_rec IN insert_customer
  LOOP
     INSERT INTO CUSTOMER_RESULTS (First_Name, Last_Name)
     VALUES (cust_rec.customer_fname, cust_rec.customer_lname);
  END LOOP;
  COMMIT;
END;
Rgs,
Rob

Answer 1

Hi
rules engine style with table that holds the logic or code SQL directly in the procedure and IF THEN ELSE with db_id. Latter is better because SQL is native and objects are checked every time procedure is compiled.
James showed the simplest way but this rather complex way gives you more flexibility between instances if ever needed.
CREATE TABLE synonym_dml(db_id number not null primary key, sql_text clob)
INSERT INTO synonym_dml VALUES (100, 'INSERT INTO customer_results (first_name, last_name) SELECT customer_fname,customer_lname FROM customer100')
INSERT INTO synonym_dml VALUES (200, 'INSERT INTO customer_results (first_name, last_name) SELECT customer_fname,customer_lname FROM customer200')
set serveroutput on size unlimited
create or replace
PROCEDURE Execute_Synonym_Dml(p_host VARCHAR2, p_db_name VARCHAR2, p_schema VARCHAR) IS
BEGIN
  FOR r IN (
    SELECT sql_text FROM synonym_dml
    --  WHERE db_id IN (
    --    SELECT d.db_id
    --    FROM t_mv_db_accounts ac, t_mv_db_instances i, t_mv_dbs d, t_mv_hosts h
    --    WHERE ac.db_id = d.db_id
    --      AND i.db_id = d.db_id
    --      AND i.host_id = h.host_id
    --      AND upper(h.host_name)      = p_hostname
    --      AND upper(d.db_name)        = p_instance
    --      AND upper(ac.account_name)  = p_schema
  LOOP
    DBMS_OUTPUT.PUT_LINE('-- executing immediately ' || r.sql_text);
    --EXECUTE IMMEDIATE r.sql_text;
  END LOOP;
END;
create or replace
PROCEDURE Execute_Synonym_Dml_Too(p_host VARCHAR2, p_db_name VARCHAR2, p_schema VARCHAR) IS
  PROCEDURE DB_ID_100 IS
  BEGIN
    DBMS_OUTPUT.PUT_LINE('-- executing DB_ID_100');
    --INSERT INTO customer_results (first_name, last_name) SELECT customer_fname,customer_lname FROM customer100;
  END;
  PROCEDURE DB_ID_200 IS
  BEGIN
    DBMS_OUTPUT.PUT_LINE('-- executing DB_ID_200');
    --INSERT INTO customer_results (first_name, last_name) SELECT customer_fname,customer_lname FROM customer200;
  END;
BEGIN
  FOR r IN (
    SELECT 100 db_id FROM dual
    --  SELECT d.db_id
    --  FROM t_mv_db_accounts ac, t_mv_db_instances i, t_mv_dbs d, t_mv_hosts h
    --  WHERE ac.db_id = d.db_id
    --    AND i.db_id = d.db_id
    --    AND i.host_id = h.host_id
    --    AND upper(h.host_name)      = p_hostname
    --    AND upper(d.db_name)        = p_instance
    --    AND upper(ac.account_name)  = p_schema
  LOOP
    IF (r.db_id = 100) THEN
      DB_ID_100;
    ELSIF (r.db_id = 200) THEN
      DB_ID_200;
    ELSE
      RAISE_APPLICATION_ERROR(-20001, 'Unknown DB_ID ' || r.db_id);
    END IF;
  END LOOP;
END;
EXECUTE Execute_Synonym_Dml('demo','demo','demo');
EXECUTE Execute_Synonym_Dml_Too('demo','demo','demo');
DROP TABLE synonym_dml PURGE
DROP PROCEDURE Execute_Synonym_Dml
table SYNONYM_DML created.
1 rows inserted.
1 rows inserted.
PROCEDURE EXECUTE_SYNONYM_DML compiled
PROCEDURE EXECUTE_SYNONYM_DML_TOO compiled
anonymous block completed
-- executing immediately INSERT INTO customer_results (first_name, last_name) SELECT customer_fname,customer_lname FROM customer100
-- executing immediately INSERT INTO customer_results (first_name, last_name) SELECT customer_fname,customer_lname FROM customer200
anonymous block completed
-- executing DB_ID_100
table SYNONYM_DML dropped.
procedure EXECUTE_SYNONYM_DML dropped.