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Question and Answer

Chris Saxon

Thanks for the question, Rahul.

Asked: March 20, 2019 - 12:57 pm UTC

Last updated: December 11, 2020 - 5:50 pm UTC

Version: 11g

Viewed 1000+ times

You Asked

Why is this statement returning value - 

select * from (
  SELECT 'AAaaanders4n' name
  FROM dual
)
WHERE REGEXP_LIKE (name, '^[A]{1}');


I have given {1} in regexp_like, still this statement returns 'AAaaanders4n'

and Chris said...

Because you're asking it to return rows where name has one uppercase A at the start. Which AAaaanders4n does.

What exactly are you trying to do here?

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Comments

Regexp_like Updates

Rahul K R, March 21, 2019 - 5:35 am UTC

I wanted to fetch only those which has only 1 A in the start.

For Ex:
select * from (SELECT 'AAaaaanders4n' name
FROM dual)
WHERE REGEXP_LIKE (name, 'a{1,3}');

This returns AAaaaanders4n where as it has more than 3a's. I assume {1,3} means it will search for pattern 'a' atleast once upto 3 times but I have 4 a's.

Am I missing something here?
Chris Saxon
March 21, 2019 - 9:34 am UTC

Then search for strings starting with A, followed by a character that's not A:

select * from (
  SELECT 'AAaaaanders4n' name
  FROM dual
  union all
  SELECT 'Alexander' name
  FROM dual
)
WHERE REGEXP_LIKE (name, '^A[^A]');

NAME        
Alexander

regexp_like dobuts

Sunny, December 11, 2020 - 9:49 am UTC

I have doubt how and when to use "[]" and "()".
can you show me easy way to understand or best example?
I refer oracle doc but not understand this.
Chris Saxon
December 11, 2020 - 5:50 pm UTC

The square brackets supply a set of characters to match. This could be a character class (such as :upper: - all uppercase letters) or a range of values (0-9 - the digits between zero and nine).

Regular parentheses mark a group. You have to have an exact match for the characters in the group.

So

[a-z] => any (lowercase) letter from a to z
(a-z) => match the exact string "a-z" (a hyphen z)

select * from (
  SELECT 'AAaaanders4n' name
  FROM dual
)
where regexp_like (name, '[a-z]{1}');

NAME           
AAaaanders4n  

select * from (
  SELECT 'AAaaanders4n' name
  FROM dual
)
where regexp_like (name, '(a-z){1}');

no rows selected

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