How to add leading zero in a number in Oracle SQL query?

You could do it in two ways.

Method 1

Using LPAD.

For example,

SQL> WITH DATA(num) AS(
  2  SELECT 540 FROM dual UNION ALL
  3  SELECT 60 FROM dual UNION ALL
  4  SELECT 2 FROM dual
  5  )
  6  SELECT num, lpad(num, 5, '0') num_pad FROM DATA;

       NUM NUM_P
---------- -----
       540 00540
        60 00060
         2 00002

SQL>

The WITH clause is only to build sample data for demo, in your actual query just do:

lpad(removal_count, 5, '0')

Remember, a number cannot have leading zeroes. The output of above query is a string and not a number.

Method 2

Using TO_CHAR and format model:

SQL> WITH DATA(num) AS(
  2  SELECT 540 FROM dual UNION ALL
  3  SELECT 60 FROM dual UNION ALL
  4  SELECT 2 FROM dual
  5  )
  6  SELECT num, to_char(num, '00000') num_pad FROM DATA;

       NUM NUM_PA
---------- ------
       540  00540
        60  00060
         2  00002

SQL>

Update : To avoid the extra leading space which is used for minus sign, use FM in the TO_CHAR format:

Without FM:

SELECT TO_CHAR(1, '00000') num_pad,
  LENGTH(TO_CHAR(1, '00000')) tot_len
FROM dual;

NUM_PAD    TOT_LEN
------- ----------
 00001           6 

With FM:

SELECT TO_CHAR(1, 'FM00000') num_pad,
  LENGTH(TO_CHAR(1, 'FM00000')) tot_len
FROM dual;

NUM_PAD    TOT_LEN
------- ----------
00001            5