I'm trying to use the Oracle `REGEXP_REPLACE` function to replace a whitespace (which is in the middle of a string) with an empty string.

One of my columns contains strings like the following one.

* *[alphanumeric][space][digits][space][alpha]* (eg. `R4SX 315 GFX`)

Now, I need to replace ONLY the second whitespace (the whitespace after the digits) with an empty string (i.e. `R4SX 315 GFX` --> `R4SX 315GFX`)

To achieve this, I tried the following code:

```
SELECT REGEXP_REPLACE(
   'R4SX 315 GFX', 
   '([:alphanum:])\s(\d)\s([:alpha:])', 
   '\1 \2\3') "REPLACED" 
FROM dual;

```

However, the result that I get is the same as my input (i.e. `R4SX 315 GFX`).
Can someone please tell me what I have done wrong and please point me in the right direction.

Thanks in advance.