This is useful when you need the whole RE to have a greediness attribute

different from what's deduced from its elements. As an example,

suppose that we are trying to separate a string containing some digits

into the digits and the parts before and after them. We might try to

do that like this:

<screen>

SELECT regexp_matches('abc01234xyz', '(.*)(\d+)(.*)');

<lineannotation>Result: </lineannotation><computeroutput>{abc0123,4,xyz}</computeroutput>

</screen>

That didn't work: the first <literal>.*</> is greedy so

it <quote>eats</> as much as it can, leaving the <literal>\d+</> to

match at the last possible place, the last digit. We might try to fix

that by making it non-greedy:

<screen>

SELECT regexp_matches('abc01234xyz', '(.*?)(\d+)(.*)');

<lineannotation>Result: </lineannotation><computeroutput>{abc,0,""}</computeroutput>

</screen>

That didn't work either, because now the RE as a whole is non-greedy

and so it ends the overall match as soon as possible. We can get what

we want by forcing the RE as a whole to be greedy:

<screen>

SELECT regexp_matches('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');

<lineannotation>Result: </lineannotation><computeroutput>{abc,01234,xyz}</computeroutput>

</screen>

Controlling the RE's overall greediness separately from its components'

greediness allows great flexibility in handling variable-length patterns.

When deciding what is a longer or shorter match,

match lengths are measured in characters, not collating elements.