Re: Detecting repeated phrase in a string - Mailing list pgsql-general

On 2021-12-09 12:38:15 +0000, Shaozhong SHI wrote:
> Does anyone know how to detect repeated phrase in a string?

Use regular expressions with backreferences:

bayes=> select regexp_match('foo wikiwiki bar', '(.+)\1');
╔══════════════╗
║ regexp_match ║
╟──────────────╢
║ {o}          ║
╚══════════════╝
(1 row)

"o" is repeated in "foo".

bayes=> select regexp_match('fo wikiwiki bar', '(.+)\1');
╔══════════════╗
║ regexp_match ║
╟──────────────╢
║ {wiki}       ║
╚══════════════╝
(1 row)

"wiki" is repeated in "wikiwiki".

bayes=> select regexp_match('fo wikiwi bar', '(.+)\1');
╔══════════════╗
║ regexp_match ║
╟──────────────╢
║ (∅)          ║
╚══════════════╝
(1 row)

nothing is repeated.

Adjust the expression within parentheses if you want to match somethig
more specific than any sequence of one or more characters.

        hp

--
   _  | Peter J. Holzer    | Story must make more sense than reality.
|_|_) |                    |
| |   | hjp@hjp.at         |    -- Charles Stross, "Creative writing
__/   | http://www.hjp.at/ |       challenge!"