Waiting for PostgreSQL 14 – Support negative indexes in split_part().

On 13rd of November 2020, Tom Lane committed patch:

Support negative indexes in split_part().
 
This provides a handy way to get, say, the last field of the string.
Use of a negative index in this way has precedent in the nearby
left() and right() functions.
 
The implementation scans the string twice when N < -1, but it seems
likely that N = -1 will be the huge majority of actual use cases,
so I'm not really excited about adding complexity to avoid that.
 
Nikhil Benesch, reviewed by Jacob Champion; cosmetic tweakage by me
 
Discussion: https://postgr.es/m/cbb7f861-6162-3a51-9823-97bc3aa0b638@gmail.com

This is pretty cool.

Let's assume you have a dot separated string, like a hostname blob.home.depesz.com.

If you'd want to get last part, previously, you'd have to resort to using regexps or some other trickery.

Now, though, you can easily:

$ SELECT split_part('blob.home.depesz.com', '.', -1);
 split_part 
────────────
 com
(1 ROW)

Same way you can get 2nd to last:

$ select split_part(‘blob.home.depesz.com', ‘.', -2);
split_part
────────────
depesz
(1 row)

Very cool. Not huge change, but a welcome one definitely. Thanks to all involved.

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