Case just give me the same date :( - sql

Question

This CASE only shows me the same date '01 / 01/2999 ', I need to get this date '01 / 01/2999' only when the date is less '01 / 01/1950 '.
If someone can help me, I feel so grateful
to_char((
CASE
WHEN to_date(RM.REME_FECHA_ENTREGA,'DD/MM/YYYY') <= to_date('01/01/1950','DD/MM/YYYY')
THEN
to_date('01/01/2999','DD/MM/YYYY')
ELSE
to_date(RM.REME_FECHA_ENTREGA,'DD/MM/YYYY')
END) ,'DD/MM/YYYY')
as FechaEntregaRemesa

Answer 1

This is because you're doing implicit date conversions, and your NLS_DATE_FORMAT has a two-digit year, e.g. 'DD/MM/YY' or this one:
alter session set nls_date_format = 'DD-Mon-RR';
-- CTE to generate two dummy values
with RM (REME_FECHA_ENTREGA) as (
select date '1950-01-01' from dual
union all select date '1950-01-02' from dual
)
-- your query plus the original date value
select to_char(RM.REME_FECHA_ENTREGA, 'SYYYY-MM-DD') as REME_FECHA_ENTREG,
to_char((
CASE
WHEN to_date(RM.REME_FECHA_ENTREGA,'DD/MM/YYYY') <= to_date('01/01/1950','DD/MM/YYYY')
THEN
to_date('01/01/2999','DD/MM/YYYY')
ELSE
to_date(RM.REME_FECHA_ENTREGA,'DD/MM/YYYY')
END) ,'DD/MM/YYYY')
as FechaEntregaRemesa
from rm;
REME_FECHA_ FECHAENTRE
----------- ----------
1950-01-01 01/01/2999
1950-01-02 01/01/2999
With a 4-digit format it works as you expect:
alter session set nls_date_format = 'DD/MM/YYYY';
...
REME_FECHA_ FECHAENTRE
----------- ----------
1950-01-01 01/01/2099
1950-01-02 02/01/1950
When you do
to_date(RM.REME_FECHA_ENTREGA,'DD/MM/YYYY')
you're actually really doing:
to_date(to_char(RM.REME_FECHA_ENTREGA, '<NLS_DATE_FORMAT>'),'DD/MM/YYYY')
which is why you see the issue with a 2-digit year model. The implicit to_char(RM.REME_FECHA_ENTREGA, 'DD-MON-RR') will give a string like '01-JAN-50'. When you pass that string back into to_date() with a YYYY format model it's interpreted as year 0050, so it's always going to be before 1950.
"Oracle Database converts strings to dates with some flexibility", which is not always helpful... here it isn't complaining that you've supplied two digits for a 4-digit model, or that (in my example) you've passed a month abbreviation instead of a month number. (You can change the behaviour with the FM/FX modifiers, but it's flexible by default.)
You may be tempted to use alter session as I did for this demo, but shouldn't rely on NLS settings as you usually have no control over what other users' settings will be. (I suspect you didn't realise you were in this query, but it's still something to watch out for.) Always use explicit conversion and full format models when you have to convert dates to strings and vice versa.
But you don't need to convert your existing date value at all. It's a date, so leave it alone. You can also use date literals for the fixed values to avoid any ambiguity and for a bit less typing:
to_char(
CASE
WHEN RM.REME_FECHA_ENTREGA <= date '1950-01-01'
THEN
date '2099-01-01'
ELSE
RM.REME_FECHA_ENTREGA
END,'DD/MM/YYYY')
as FechaEntregaRemesa
...
REME_FECHA_ FECHAENTRE
----------- ----------
1950-01-01 01/01/2099
1950-01-02 02/01/1950
or even (modifying #expenguin's suggestion) only using dates when you have to:
CASE
WHEN RM.REME_FECHA_ENTREGA <= date '1950-01-01'
THEN
'01/01/2099'
ELSE
TO_CHAR(RM.REME_FECHA_ENTREGA, 'DD/MM/YYYY')
END as FechaEntregaRemesa

Answer 2

EDIT: so it looks like you don't even need the to_char if your data is already stored as text, and you shouldn't need it for comparing. Converting to a date is the only thing you should need for comparing the string literal.
so we take OP's Code:
to_char((
CASE
WHEN to_date(RM.REME_FECHA_ENTREGA,'DD/MM/YYYY') <= to_date('01/01/1950','DD/MM/YYYY')
THEN
to_date('01/01/2999','DD/MM/YYYY')
ELSE
to_date(RM.REME_FECHA_ENTREGA,'DD/MM/YYYY')
END) ,'DD/MM/YYYY')
as FechaEntregaRemesa
And change below
IF REME_FECHA_ENTREGA IS A DATE:
CASE
WHEN RM.REME_FECHA_ENTREGA <= date '1950-01-01'
THEN
'01/01/2099'
ELSE
to_char(RM.REME_FECHA_ENTREGA, 'MM/DD/YYYY')
END as FechaEntregaRemesa
IF REME_FECHA_ENTREGA IS A STRING:
CASE
WHEN to_date(RM.REME_FECHA_ENTREGA, 'DD/MM/YYYY') <= date '01/01/1950'
THEN
'01/01/2999'
ELSE
RM.REME_FECHA_ENTREGA
END as FechaEntregaRemesa