If they're always between 6 and 9 digits, the easiest (and probably best) way to go is using CASE.
SELECT CASE WHEN LEN(CHECK_NUM)= 6 THEN '000' WHEN LEN(CHECK_NUM) = 7 THEN '00'
WHEN
LEN(CHECK_NUM) = 8 THEN '0' ELSE '' END + CHECK_NUM
FROM TABLE
EDIT
In case the original values are numbers (int
), try something like this:
SELECT CASE WHEN LEN(CHECK_NUM)= 6 THEN '000' WHEN LEN(CHECK_NUM) = 7 THEN '00'
WHEN
LEN(CHECK_NUM) = 8 THEN '0' ELSE '' END + CAST(CHECK_NUM AS VARCHAR(9))
FROM TABLE1
Take a look at the this SQL Fiddle.