Converting Sql Server If not exists to Oracle

Question

I have a snippet of a SQL Server procedure that looks like this:

IF NOT EXISTS(SELECT ID FROM IDTABLE WHERE ID=@ID)
BEGIN
    DECLARE @MSG VARCHAR(100)
    SET @MSG = 'The ID (ID: ' + CONVERT(VARCHAR(50), @ID) + ') does not exist'
    EXEC SP_LOGAUDITMESSAGE 'Warning', 'Bill report', @MSG
    SET @RETVAL = 0
    RETURN
END

This runs the select query and if no results are returned, runs the begin/end block. It declares a message variable and sends this, along with some other values, to a logging stored procedure before returning from the method.

I'm on a project now though where I have to convert all of this stuff into Oracle (which I have zero familiarity with). I ran it through the scratch editor in Sql Developer and got this:

BEGIN
    SELECT 1
    INTO v_temp
    FROM DUAL
    WHERE NOT EXISTS
      ( SELECT ID FROM ID WHERE IDTABLE = v_ID
      );
  EXCEPTION
  WHEN OTHERS THEN
    NULL;
  END;
  IF v_temp = 1 THEN
    DECLARE
      v_MSG VARCHAR2(100);
    BEGIN
      v_MSG := 'The ID (ID: ' || UTILS.CONVERT_TO_VARCHAR2(v_ID,50) || ') does not exist' ;
      BEGIN
        SP_LOGAUDITMESSAGE('Warning', 'Bill report', v_MSG) ;
      EXCEPTION
      WHEN OTHERS THEN
        v_sys_error := SQLCODE;
      END;
      v_RETVAL := 0 ;
      RETURN;
    END;
  END IF;

Now, I get what it's trying to do - it's just taking a few more steps to do it, saving the results of the select statement into v_temp and then if it is set to equal 1, running the if block.

However, I've a few queries. Firstly, some simple googling has taught me that the first Exception block (when others then null) is terrible practice. What would an alternative be in this situation, or is it acceptable given the following if statement? Secondly, is this entire rewrite necessary, or is it possible to amalgamate the if and select statements (similar to the SQL above) to make things a little more succinct?

Answer 1

Something like this:

DECLARE
  v_MSG   VARCHAR2(100);
  v_temp  integer;
BEGIN

  SELECT count(*)
    into v_temp
  FROM COF 
  WHERE ID = v_ID

  IF v_temp = 0 THEN
    v_MSG := 'The ID (ID: ' || to_char(v_id) || ') does not exist' ;
    SP_LOGAUDITMESSAGE('Warning', 'Bill report', v_MSG) ;
    v_RETVAL := 0;
  ELSE 
    v_RETVAL := 1; -- not sure about this though
  END IF;

RETURN;

EXCEPTION
   WHEN OTHERS THEN
      v_sys_error := SQLCODE;
   raise;
END;

Changes:

• the test if the id exists is better done using a count(*) as that doesn't throw an exception if the id is not found
• don't nest the declare blocks. That is confusing.
• I would use only a single exception handler for the whole procedure