How can I validate a date using sql

Question

How can I validate a date using sql or pl/sql
select to_date('01/01/2009','mm/dd/yyyy') from dual this is a good date
but how can I check for a bad date
select to_date('0a/01/2009','mm/dd/yyyy') from dual
Howard

Answer 1

William Robertson wrote:
It'll be complicated in pure SQL, as you'll have to parse out day, month and year and then validate the day against the month and year bearing in mind the rules for leap years. It would be simpler to write a PL/SQL function and call that.Nah, not that complicated, you just need to generate a calender to validate against.
SQL> ed
Wrote file afiedt.buf
  1  with yrs as (select rownum-1 as yr from dual connect by rownum <= 100)
  2      ,mnth as (select rownum as mn, case when rownum in (4,6,9,11) then 30
  3                            when rownum = 2 then 28
  4                       else 31
  5                       end as dy
  6                from dual
  7                connect by rownum <= 12)
  8      ,cent as (select (rownum-1) as cen from dual connect by rownum <= 21)
  9      ,cal as (select cen, yr, mn,
10                      case when ((yr = 0 and mod(cen,400) = 0)
11                             or (mod(yr,4) = 0 and yr > 0))
12                            and mn = 2 then dy+1
13                      else dy
14                      end as dy
15               from cent, yrs, mnth)
16  --
17      ,dt as (select '&date_dd_mm_yyyy' as dt from dual)
18  --
19  select case when cal.cen is null then 'Invalid Date'
20              when not regexp_like(dt,'^[0-9]{1,2}[\/.-_][0-9]{1,2}[\/.-_][0-9]{4}$') then 'Invalid Date'
21         else dt
22         end as dt
23  from dt left outer join
24               cal on (to_number(regexp_substr(dt,'[0-9]+')) between 1 and cal.dy
25                   and to_number(regexp_substr(dt,'[0-9]+',1,2)) = cal.mn
26                   and floor(to_number(regexp_substr(dt,'[0-9]+',1,3))/100) = cal.cen
27*                  and to_number(substr(regexp_substr(dt,'[0-9]+',1,3),-2)) = cal.yr)
SQL> /
Enter value for date_dd_mm_yyyy: a1/02/2008
old  17:     ,dt as (select '&date_dd_mm_yyyy' as dt from dual)
new  17:     ,dt as (select 'a1/02/2008' as dt from dual)
DT
Invalid Date
SQL> /
Enter value for date_dd_mm_yyyy: 01/02/2008
old  17:     ,dt as (select '&date_dd_mm_yyyy' as dt from dual)
new  17:     ,dt as (select '01/02/2008' as dt from dual)
DT
01/02/2008
SQL> /
Enter value for date_dd_mm_yyyy: 29/02/2008
old  17:     ,dt as (select '&date_dd_mm_yyyy' as dt from dual)
new  17:     ,dt as (select '29/02/2008' as dt from dual)
DT
29/02/2008
SQL> /
Enter value for date_dd_mm_yyyy: 30/02/2008
old  17:     ,dt as (select '&date_dd_mm_yyyy' as dt from dual)
new  17:     ,dt as (select '30/02/2008' as dt from dual)
DT
Invalid Date
SQL> /
Enter value for date_dd_mm_yyyy: 29/02/2009
old  17:     ,dt as (select '&date_dd_mm_yyyy' as dt from dual)
new  17:     ,dt as (select '29/02/2009' as dt from dual)
DT
Invalid Date
SQL> /
Enter value for date_dd_mm_yyyy: 28/02/2009
old  17:     ,dt as (select '&date_dd_mm_yyyy' as dt from dual)
new  17:     ,dt as (select '28/02/2009' as dt from dual)
DT
28/02/2009
SQL> /
Enter value for date_dd_mm_yyyy: 0a/01/2009
old  17:     ,dt as (select '&date_dd_mm_yyyy' as dt from dual)
new  17:     ,dt as (select '0a/01/2009' as dt from dual)
DT
Invalid Date
SQL> /
Enter value for date_dd_mm_yyyy: 00/01/2009
old  17:     ,dt as (select '&date_dd_mm_yyyy' as dt from dual)
new  17:     ,dt as (select '00/01/2009' as dt from dual)
DT
Invalid Date
SQL>