INSERTing REVERSE(Date) has interesting results. UPDATing, however, seems to choose a valid DATE.

– Purpose : To return a string in conventional English language sentence format (letter case) (as opposed to INITCAP)
– It will leave words that contain numbers, and a select range of characters, as they are
– Usage : Small scale data conversion and display
– Limitations : Does not use any dictionary - based purely on sentence conventions
– Does not cope with Names and acronyms, but a special character (eg ^)
– can be added to a word and subsequently removed to provide special formatting
– Author : Rob Spaanderman 25/01/07
– Notes : The lions share of the convoluted code is to accommodate special words - words with non-alpha’s in them
– It could be somewhat simplified if we were to ignore the IT potential for codes etc.
– This function can be modified to suit your particular situation
– I have tried to make it easily modifiable - by just changing the lists of special characters to suit

IS
c_translate_mask CONSTANT VARCHAR2(20) := ‘~~~~~~~~~~~~~~~~~~~’; — works in tandem with the word skip list and the translate check
c_translate_check CONSTANT VARCHAR2(1) := ‘~’; — if this is changed, the translate mask must be changed
c_upper_after_space CONSTANT VARCHAR2(20) := ‘.?!;:’; — English language symbols denoting the end of a sentence (; and : are debateable)
c_upper_after_char CONSTANT VARCHAR2(20) := ‘”(’; — Other characters that may preceed that start of a sentence or word with uppercase first letter
c_skip_word_with CONSTANT VARCHAR2(20) := NVL(pi_skip_word_with,’0123456789_-&$@%/\’); — characters can be added or removed (or overridden) to change which words are ommitted from formatting

v_length NUMBER(4) := LENGTH(pi_input_string); — there are multiple refences to the length
v_first_blank_pos NUMBER(4) := 1;
v_next_blank_pos NUMBER(4) := INSTR(pi_input_string,’ ‘);
v_previous_letter VARCHAR2(1) := SUBSTR(pi_input_string,1,1);
v_current_letter VARCHAR2(1) := v_previous_letter; — when starting, we start at position 1, so everything starts with letter 1
v_next_letter VARCHAR2(1) := v_previous_letter;
v_result_string VARCHAR2(2000);
v_current_word VARCHAR2(2000); — used to determine whether we need to leave a special word alone or not

BEGIN
FOR v_position IN 1..v_length LOOP
IF v_current_letter = ‘ ‘ — between words
OR v_position = 1 THEN — first time around
v_first_blank_pos := v_position;
v_next_blank_pos := INSTR(pi_input_string,’ ‘,v_first_blank_pos + 1);
IF v_next_blank_pos = 0 THEN — probably the end of the sentence which will have no space
v_next_blank_pos := v_length;
END IF;
— Extract the next word in the sentence - used to determine if we need to leave it alone or not
v_current_word := SUBSTR(pi_input_string, v_first_blank_pos, v_next_blank_pos - v_first_blank_pos);
END IF;
— We check to see if there any special characters in the word - if not, do the formatting, else skip the formatting
IF INSTR(TRANSLATE(v_current_word, c_skip_word_with, c_translate_mask), c_translate_check) = 0 THEN
IF (v_current_letter = ‘ ‘
AND INSTR(c_upper_after_space,v_previous_letter) <> 0
OR v_position = 1)
OR INSTR(c_upper_after_char, v_current_letter) <> 0 THEN
v_next_letter := UPPER(v_next_letter);
ELSE
v_next_letter := LOWER(v_next_letter);
END IF;
END IF;
— The “next letter” contains either the uppered, the lowered, or the left alone value
v_result_string := v_result_string || v_next_letter;
— Move the three operational letters along the sequence
v_previous_letter := v_current_letter;
v_current_letter := v_next_letter;
v_next_letter := SUBSTR(pi_input_string,v_position + 1,1);
END LOOP;
RETURN (v_result_string);
END;
/

SQL> create table t (x date);

Table created.

SQL> insert into t values (reverse(sysdate));

1 row created.

SQL> select * from t;

X
---------
20-BINARY

SQL> select to_char(x,'mm-dd-yyyy') y from t;

Y
----------
00-00-0000

Since REVERSE preserves the datatype, you end up with a date that is not really a date. You are actually, in a way, bypassing datatype validation. Interesting!

You’re right Gary, no wonder it is still undocumented!

UPDATE table SET date_col = REVERSE(date_col) 

and watch all the errors as people try to select the data.
There’s a reason why somethings are best left undocumented.

Seriously, I think the main use of this is behind the scenes for reverse key indexes.
http://asktom.oracle.com/pls/ask/f?p=4950:8:2175155135156691628::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:6163160472530
I’d be surprised if it is ever ‘documented’ for any other use.