How to select a random row with for update?

Question

Hi,
I have a package that needs to assign a random, reusable number (ID) that is not currently being used - to a procedure.
I'm trying to simulate a pool of numbers (IDs) using a table that has an ID and IS_USED columns.
How do I do:
select a random ID (random row)
from pool_table
where IS_USED is 0 (not taken)
FOR UPDATEThe for update is to lock the row from being taken by another process calling the package.
OR:
Can I simulate a pool of numbers with a different object (not a table)?
I need the numbers to be coherent between sessions (thus package variables will not work) and only one session uses the same ID at any given time. When it finishes the number becomes available for further runs.
Thanks.
Edited by: Pyrocks on Nov 7, 2010 10:45 AM

Answer 1

This works on Oracle 11g (probably on 10g too, but I haven't tested):
CREATE OR REPLACE PACKAGE REUSABLE_RANDOM_NUMBERS
IS
  FUNCTION GET_NUMBER RETURN NUMBER;
END REUSABLE_RANDOM_NUMBERS;
create or replace
PACKAGE BODY REUSABLE_RANDOM_NUMBERS
IS
  TYPE NUM_TABLE_TYPE IS TABLE OF CHAR INDEX BY PLS_INTEGER;
  MIN_VALUE CONSTANT PLS_INTEGER := 0;
  max_value CONSTANT PLS_INTEGER := 10;
  NUM_TABLE NUM_TABLE_TYPE;
  FUNCTION GET_NUMBER RETURN NUMBER
  IS
    num PLS_INTEGER;
  BEGIN
    FOR I IN 1 .. 100 LOOP
       NUM := DBMS_RANDOM.VALUE( min_value, max_value );
       IF NOT NUM_TABLE.EXISTS( NUM ) THEN
          NUM_TABLE( NUM ) := 'X';
          RETURN NUM;
       END IF;
    END LOOP;
    FOR I IN MIN_VALUE .. MAX_VALUE LOOP
      IF NOT NUM_TABLE.EXISTS( i ) THEN
          NUM_TABLE( i ) := 'X';
          RETURN i;
       END IF;
    END LOOP;
    RAISE_APPLICATION_ERROR( -20991, 'All possible values have ben used, cannot assign a new one' );
  END;
END REUSABLE_RANDOM_NUMBERS;
SELECT REUSABLE_RANDOM_NUMBERS.GET_NUMBER
FROM DUAL
connect by level <= 11;
GET_NUMBER            
3                     
4                     
6                     
2                     
1                     
7                     
8                     
0                     
9                     
5                     
10                    
11 rows selected
SELECT REUSABLE_RANDOM_NUMBERS.GET_NUMBER
FROM DUAL;
Error starting at line 44 in command:
SELECT REUSABLE_RANDOM_NUMBERS.GET_NUMBER
FROM DUAL
Error report:
SQL Error: ORA-20991: All possible values have ben used, cannot assign a new one
ORA-06512: przy "TEST.REUSABLE_RANDOM_NUMBERS", linia 26