Calling a Procedure and Function over a db link

Question

I am experiencing some errors with the following and would greatly appreciate the advice of some experts here.
My use-case is to insert some records into a table via a database link. The records to be inserted will be queried from an identical table in the local data dictionary. Everything works, but occasionally I will get a unique constraint violation if I try to insert a duplicate record so I wrote a simple function to check for the scenario. My issue is that I can run my procedure using the db link and I can run my function using the db link, but I can't use them both together without getting errors.
My test case just uses the standard emp table:
create or replace procedure test_insert(p_instance varchar2)
IS
l_sql varchar2(4000);
begin
    l_sql := 'insert into EMP@'||p_instance||' (EMPNO, ENAME, JOB, MGR, SAL, DEPTNO) (Select EMPNO, ENAME, JOB, MGR, SAL, DEPTNO from EMP)';
execute immediate l_sql;
END;
BEGIN
test_insert('myLink');
END;
This works fine and the insert occurs without any issues.
If I run the same procedure a second time I get:
00001. 00000 -  "unique constraint (%s.%s) violated" which is what I expect since EMPNO has a unique constraint. So far so good.
Now I create a function to test whether the record exists:
create or replace function record_exists(p_empno IN NUMBER, p_instance IN varchar2) return number
IS
l_sql varchar2(4000);
l_count number;
BEGIN
l_sql := 'select count(*) from EMP@'||p_instance||' where empno = '||p_empno;
execute immediate l_sql into l_count;
IF
l_count > 0
THEN return 1;
ELSE
return 0;
END IF;
END;
I test this as follows:
select record_exists(8020, 'myLink') from dual;
RECORD_EXISTS(8020,'myLink')
                                          1
That works ok, so now I will add that function to my procedure:
create or replace procedure test_insert(p_instance varchar2)
IS
l_sql varchar2(4000);
begin
    l_sql := 'insert into EMP@'||p_instance||' (EMPNO, ENAME, JOB, MGR, SAL, DEPTNO) (Select EMPNO, ENAME, JOB, MGR, SAL, DEPTNO from EMP WHERE record_exists( EMPNO, '''||p_instance||''') = 0)';
execute immediate l_sql;
END;
I test this as follows:
BEGIN
test_insert('myLink');
END;
Result is:
Error report:
ORA-02069: global_names parameter must be set to TRUE for this operation
ORA-06512: at "FUSION.TEST_INSERT", line 6
ORA-06512: at line 2
02069. 00000 -  "global_names parameter must be set to TRUE for this operation"
*Cause:    A remote mapping of the statement is required but cannot be achieved
           because global_names should be set to TRUE for it to be achieved
*Action:   Issue alter session set global_names = true if possible
I don't know why I am getting this. The function works, the procedure works, but when I combine them I get an error. If I set the global names parameter to true and then rerun this I get:
02085. 00000 -  "database link %s connects to %s"
*Cause:    a database link connected to a database with a different name.
           The connection is rejected.
*Action:   create a database link with the same name as the database it
           connects to, or set global_names=false.
Any advice is much appreciated. I don't understand why I can run the procedure and the function each separately over the db link but they don't work together.
thank you,
john

Answer 1

The proper procedure depends on what how you define failure and what it should mean - error back to caller, log and continue, just continue. Constraints are created to ensure invalid data does not get into a table. Generally they provide the most efficient mechanism for checking for invalid data, and return useful exceptions which the caller can handle. You are also doubling the work load of the uniqueness check by adding in your own check.
In general I'd say use Exceptions, they are your friend