'?': match exactly zero or one repetition

SQL> --'?': match exactly zero or one repetition
SQL>
SQL> SELECT REGEXP_SUBSTR('Yababa dababa do','a.?a') FROM dual;

REG
---
aba

SQL>

1.	'.' matches anything
2.	REGEXP_INSTR(description,'F.')
3.	REGEXP_INSTR(description,'e.e'): Find a letter and then whatever until there was another of the same letter
4.	REGEXP_INSTR(description,'i.i'): 'i' followed by any one character, followed by another 'i'
5.	REGEXP_SUBSTR('Yababa dababa do','a.a')
6.	REGEXP_SUBSTR('abbbb','ab+')
7.	REGEXP_SUBSTR('a','ab+')
8.	REGEXP_SUBSTR('abbbb','ab*') (2)
9.	To see the difference between '*' and '+'
10.	'+': match one or more repetitions
11.	'*' (match zero or more repetitions)
12.	REGEXP_INSTR(description, 'e.+e'): An 'e' followed by any number of other characters and then another 'e'
13.	REGEXP_SUBSTR(description,'e.*e')
14.	Use the non-greedy '?'

'?': match exactly zero or one repetition : Wild Card « Regular Expressions « Oracle PL / SQL