Question

I have a table that has IDs and Strings and I need to be able to properly index for searching for the end of the strings. How we are currently handling it is copying the information into another table and reversing each string and indexing it normally. What I would like to do is use some kind of index that allows to search in reverse.

Example

Data: 
F7421kFSD1234 
d7421kFSD1235 
F7541kFSD1236 
d7421kFSD1234
F7421kFSD1235 
b8765kFSD1235 
d7421kFSD1234

The way our users usually input thier search is something along the lines of…

*1234

By reversing the strings (and the search string: 4321*) I could find what I am looking for without completely scanning the whole table. My question is: Is making a second table the best way of doing this?

Is there a way to reverse index?
Ive tried an index like this…

create index REVERSE_STR_IDX on TABLE(STRING) REVERSE;

but oracle doesn’t seem to be using it according to the Explain Plan.

Thanks in advance for the help.

---

Update:

I did have a problem with unicode characters not being reversed correctly. The solution to this was casting them.

Example:

select REVERSE(cast(string AS varchar2(2000)))
from tbl 
where id = 1

Answer 1

There is the myth that a reverse key index can be used for that, however, I’ve never seen that in action.

I would try a “manual” function based index.

CREATE INDEX REVERSE_STR_IDX on TBL(reverse(string));

SELECT *
  FROM TBL
 WHERE reverse(string) LIKE '4321%';