Hi, Peter, Interesting.
On Thu, 3 Feb 2022 at 19:48, Peter J. Holzer <hjp-pgsql@xxxxxx> wrote:
On 2022-02-02 08:00:00 +0000, Shaozhong SHI wrote:
> regex - Regular _expression_ For Duplicate Words - Stack Overflow
>
> Is there any example in Postgres?
It's pretty much the same as with other regexp dialects: User word
boundaries and a word character class to match any word and then use a
backreference to match a duplicate word. All the building blocks are
described on
https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-POSIX-REGEXP
and except for [[:<:]] and [[:>:]] for the word boundaries, they are
also pretty standard.
So
[[:<:]] start of word
([[:alpha:]]+) one or more alphabetic characters in a capturing group
[[:>:]] end of word
\W+ one or more non-word characters
[[:<:]] start of word
\1 the content of the first (and only) capturing group
[[:>:]] end of word
All together:
select * from t where t ~ '[[:<:]]([[:alpha:]]+)[[:>:]]\W[[:<:]]\1[[:>:]]';
Give a good example if you can.
Regards,
David
