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Implement regexp_match(), a simplified alternative to regexp_matches().

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regexp_match() is like regexp_matches(), but it disallows the 'g' flag
and in consequence does not need to return a set.  Instead, it returns
a simple text array value, or NULL if there's no match.  Previously people
usually got that behavior with a sub-select, but this way is considerably
more efficient.

Documentation adjusted so that regexp_match() is presented first and then
regexp_matches() is introduced as a more complicated version.  This is
a bit historically revisionist but seems pedagogically better.

Still TODO: extend contrib/citext to support this function.

Emre Hasegeli, reviewed by David Johnston

Discussion: <CAE2gYzy42sna2ME_e3y1KLQ-4UBrB-eVF0SWn8QG39sQSeVhEw@mail.gmail.com>
This commit is contained in:
Tom Lane
2016-08-17 18:32:56 -04:00
parent 2d7e591007
commit cf9b0fea5f
9 changed files with 253 additions and 94 deletions
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7
src/test/regress/sql/regex.sql
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@ -25,6 +25,13 @@ select substring('asd TO foo' from ' TO (([a-z0-9._]+|"([^"]+|"")+")+)');
select substring('a' from '((a))+');
select substring('a' from '((a)+)');
-- Test regexp_match()
select regexp_match('abc', '');
select regexp_match('abc', 'bc');
select regexp_match('abc', 'd') is null;
select regexp_match('abc', '(B)(c)', 'i');
select regexp_match('abc', 'Bd', 'ig'); -- error
-- Test lookahead constraints
select regexp_matches('ab', 'a(?=b)b*');
select regexp_matches('a', 'a(?=b)b*');