What does this Oracle TO_CHAR format do: "FM99990.90"
Of course it is listed/documented.

Format Model Modifiers


  FM
  
  Fill mode. Oracle uses trailing blank characters and leading zeroes to
  fill format elements to a constant width. The width is equal to the
  display width of the largest element for the relevant format model:
  
  Numeric elements are padded with leading zeros to the width of the
  maximum value allowed for the element. For example, the YYYY element
  is padded to four digits (the length of '9999'), HH24 to two digits
  (the length of '23'), and DDD to three digits (the length of '366').
  
  ...


Example:

SQL&gt; select to_char(1.5, 'FM99990.90') from dual;

TO_CHAR(1
---------
1.50

SQL&gt; select to_char(1.5, '99990.90') from dual;

TO_CHAR(1
---------
     1.50

SQL&gt;