Re: Regular Expression For Duplicate Words

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.