Trap exceptions in SQL statements

Question

Hello everyone,
From time to time I find myself in a situation when I want to suppress exceptions in a plain SQL SELECT statements, to keep them from being raised and to choose some other outcome in case of error.
Let's say I have a VARCHAR2 field that in fact represents numerical information and I want to run a test if those values are valid numbers:
SELECT string FROM table WHERE ERRVL(TO_NUMBER(string), NULL) IS NULL;
or
SELECT ERRVL(TO_NUMBER(string), 'Not a valid number') FROM table;
ERRVL would be this imaginary function that evaluates expression and in case of exception outputs alternative value. Something similar to the NVL function.
Is there a such thing in Oracle SQL?
With regards,
Goran

Answer 1

I wrote something in 10.2 (I think it was) which could help you, but trying it in 10.1 just now I found it needed a few modifications to make it work. Perhaps there was a change to the regular expressions functionality between the two versions?
Anyway, here it is, it uses regular expressions to identify numbers based on data being in certain formats:
WITH data AS(
  SELECT 'ER123' value FROM dual UNION ALL
  SELECT 'EU123' value FROM dual UNION ALL
  SELECT 'er124' value FROM dual UNION ALL
  SELECT 'e11' value FROM dual UNION ALL
  SELECT 'E11' value FROM dual UNION ALL
  SELECT 'es1' value FROM dual UNION ALL
  SELECT '2.2.2' value FROM dual UNION ALL
  SELECT '2/2' value FROM dual UNION ALL
  SELECT '-43245.e4 ' value FROM dual UNION ALL
  SELECT '92872.^06' value FROM dual UNION ALL
  SELECT '92872.' value FROM dual UNION ALL
  SELECT '?92872' value FROM dual UNION ALL
  SELECT '<< invalid above | valid below >>' value FROM dual UNION ALL
  SELECT '2.7808e-05' value FROM dual UNION ALL
  SELECT ' 3.91245e+08' value FROM dual UNION ALL
  SELECT '3.91245E+08' value FROM dual UNION ALL
  SELECT '-2.55669e-06' value FROM dual UNION ALL
  SELECT '- 2.55669' value FROM dual UNION ALL
  SELECT '-255669' value FROM dual UNION ALL
  SELECT '255669.23556' value FROM dual UNION ALL
  SELECT ' 0.55669' value FROM dual UNION ALL
  SELECT '10e-04' value FROM dual UNION ALL
  SELECT '8e4' value FROM dual UNION ALL
  SELECT '1e06' value FROM dual UNION ALL
  SELECT '0.55669^-06' value FROM dual UNION ALL
  SELECT '8^4' value FROM dual UNION ALL
  SELECT '1^06' value FROM dual UNION ALL
  SELECT '0.55669^+06' value FROM dual UNION ALL
  SELECT ' 0.55669^-06' value FROM dual
SELECT
  rn, value,
  CASE WHEN regexp_instr(value2,'[Ee^]') > 0
    THEN
      To_Number(SubStr(value2,1,regexp_instr(value2,'[Ee^]')-1))
      Power(10,To_Number(SubStr(value2,regexp_instr(value2,'[Ee^]')+1)))
    ELSE To_Number(value2)
    END b
FROM (SELECT ROWNUM rn, value, REPLACE(value,' ',NULL) value2 FROM data)
WHERE regexp_like(value2,'^-?[[:digit:]]*\.?[[:digit:]]+([Ee^][-+]?[[:digit:]]+)?$');That's Ok in 10.1 for windows, I believe the following was Ok on 10.2 for linux
SELECT
  value,
  CASE WHEN regexp_instr(value,'[Ee^]') > 0
    THEN
      To_Number(SubStr(value,1,regexp_instr(value,'[Ee^]')-1))
      Power(10,To_Number(SubStr(value,regexp_instr(value,'[Ee^]')+1)))
    ELSE To_Number(value)
    END b
FROM data
WHERE regexp_like(value,'^-?\d*\.?\d+([Ee^][-+]?\d+)?$');