Oracle Regular Expressions Pocket Reference

Name

? (Question Mark) — Matches zero or one

Synopsis

The question mark (?) is very similar to the asterisk (*), except that it matches at most one occurrence of the preceding element. For example, the following returns only the first fruit:

SELECT REGEXP_SUBSTR('apple apple orange wheat',
       '((apple|orange|pear)[[:space:]]*)?')
FROM dual;

apple

Like the *, the ? can surprise you by matching where you don’t expect. In this case, if the string doesn’t begin with a fruit name, the ? will match on the empty string. See * (Asterisk) for an example of this kind of behavior.