From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Shaozhong SHI <shishaozhong(at)gmail(dot)com> |
Cc: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, pgsql-general <pgsql-general(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Can Postgres beat Oracle for regexp_count? |
Date: | 2022-02-03 05:59:36 |
Message-ID: | 205525.1643867976@sss.pgh.pa.us |
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Thread: | |
Lists: | pgsql-general |
Shaozhong SHI <shishaozhong(at)gmail(dot)com> writes:
> The following has been attempted but no luck.
> select regexp_matches('My High Street', '([A-Z][a-z]+[\s]*)+', 'g')
> It is intended to match 'My High Street, but it turned out only 'Street'
> was matched.
You've got the parentheses in the wrong place, ie inside not outside the
"+" quantifier. Per the fine manual [1], the result is determined by the
last match of quantified capturing parens.
You could avoid using any capturing parens, so that the result is
the whole match:
regression=# select regexp_matches('My High Street', '(?:[A-Z][a-z]+[\s]*)+', 'g');
regexp_matches
--------------------
{"My High Street"}
(1 row)
or you could do
regression=# select regexp_matches('My High Street', '(([A-Z][a-z]+[\s]*)+)', 'g');
regexp_matches
---------------------------
{"My High Street",Street}
(1 row)
but then you have two sets of capturing parens and you get results for
both, so you might prefer
regression=# select regexp_matches('My High Street', '((?:[A-Z][a-z]+[\s]*)+)', 'g');
regexp_matches
--------------------
{"My High Street"}
(1 row)
In any case, there's no substitute for reading the manual.
regards, tom lane
[1] https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-POSIX-REGEXP
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