format interval with to_char

Question

Following SQL command

select TO_CHAR(NVL(arg1 - arg2, TO_DSINTERVAL(\'0 00:00:00\'))) from table1

produces a result of the format: +0000000

Answer 1

I realize it's not clever at all, nor is it the special format string you're looking for, but this answer does work, given that the output is fixed length:

SELECT    SUBSTR(TO_CHAR(NVL(arg1 - arg2, TO_DSINTERVAL('0 00:00:00'))), 1, 1)
       || SUBSTR(TO_CHAR(NVL(arg1 - arg2, TO_DSINTERVAL('0 00:00:00'))), 9, 2)
       || ' '
       || SUBSTR(TO_CHAR(NVL(arg1 - arg2, TO_DSINTERVAL('0 00:00:00'))), 12, 12)
  FROM table1;

It also just truncs the fractional seconds instead of rounding, but I assume from your example they're all just zeros anyway.

This is an even greater embarrassment, but I couldn't resist:

SELECT SUBSTR(REPLACE(TO_CHAR(NVL(arg1 - arg2, TO_DSINTERVAL('0 00:00:00')))
                     , '0000000', '')
             , 1, 16)
  FROM table1;