The '?' says to match zero or one time : Meta characters « Regular Expressions Functions « Oracle PL/SQL Tutorial

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Oracle PL/SQL Tutorial » Regular Expressions Functions » Meta characters

18. 6. 20. The '?' says to match zero or one time


SQL>

SQL> SELECT REGEXP_INSTR('abc','d?') FROM dual;



REGEXP_INSTR('ABC','D?')

------------------------

                       1



SQL>

SQL> --.

SQL>

18. 6. Meta characters
	18. 6. 1.	Meta characters
	18. 6. 2.	The period may be substituted for any letter and still maintain a match
	18. 6. 3.	Use the caret-anchor to insist the matching start at the beginning of the string
	18. 6. 4.	Asking for a match for a capital 'F' followed by any character
	18. 6. 5.	The search string cannot be anchored at the beginning and then searched from some other position
	18. 6. 6.	Negating Carets
	18. 6. 7.	A '^' followed by something else like an 'l' (a lowercase 'L')
	18. 6. 8.	Match a string where 'i' is followed by any one character and followed by another 'i'
	18. 6. 9.	Regexp_Substr
	18. 6. 10.	'*' matches zero or more repetitions
	18. 6. 11.	'+' matches one or more repetitions
	18. 6. 12.	'?' matches exactly zero or one repetition
	18. 6. 13.	Asking to match an 'a' and zero or more 'b's:
	18. 6. 14.	A series of 'b's immediately following the 'a'
	18. 6. 15.	Matching at least one 'b'
	18. 6. 16.	Want an 'e' followed by any number of other characters and then another 'e'
	18. 6. 17.	REGEXP_SUBSTR(value,'e.*e')
	18. 6. 18.	Non-greedy '?'
	18. 6. 19.	Empty Strings and the ? Repetition Character
	18. 6. 20.	The '?' says to match zero or one time

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