Oracle regular expressions: search by pattern exact match

Here you can learn about finding the exact regular expression match using SQL query in Oracle. Article is made upon examples so you will be on the right track in no time.


Usually when we want to search Oracle database users table via regular expressions by email domain filter, it's easy:

SELECT * FROM users
WHERE regexp_like(mail, '@gmail\.com');

But lets say that we want to be more specific and we want to search the database for users whose name is John and last name is starting with "B". For this example, lets assume that some users email address format is "firstname.lastname@gmail.com".

If we use this statement:

SELECT * FROM users
WHERE regexp_like(mail, 'john\.b[a-zA-Z]*@gmail\.com');

The solution to this problem i very simple. We must add two special characters. One, ^ (caret), at the beginning and the other, $ (dollar), at the end of our regular expression.

Quick explanation:
^ (caret) - means that the string starts with regular expression pattern.
$ (dollar) - means that the string ends with regular expression pattern.

Knowing this correct statement should look like this:

SELECT * FROM users
WHERE regexp_like(mail, '^john\.b[a-zA-Z]*@gmail\.com$');

Using regular expressions in Oracle SQL queries, pt. I

This is an article on Oracle and using of regular expressions. Oracle has several regexp functions. Each will be described with an example below.

First things first

If you have access to existing Oracle database you can skip to the next paragraph.
If you don’t have Oracle database installed already, please follow these steps:

• register at oracle.com
• download and install latest possible Oracle Database*

Using regular expressions in Oracle

There are five regexp methods implemented in Oracle:

• REGEXP_LIKE
• REGEXP_SUBSTR
• REGEXP_REPLACE
• REGEXP_INSTR
• REGEXP_COUNT

Basically they work in exactly same way as other Oracle methods.

REGEXP functions parameters:

source - source string.

regexp - regular expression.

position - position of the character in the source string at which the match should start.

occurrence - specifies witch match to get from source string.

replacement - in REGEXP_REPLACE specifies what is the replacement for matched regexp in source string. If omitted, matching regexp value will be deleted.

return_option - in REGEXP_INSTR: set to 0 to get position of first character in match, set to 1 to get position of first character after the match.

mode - is a string of up to three (from four: i, c, n, m) characters.

• i: turns off case sensitive matching.
• c: turns on case sensitive matching.
• n: '.' match any character, including newlines. DEFAULT: any character except newlines.
• m: '^' and '$' match at the start and end of each line. DEFAULT: the match at the very start and the very end of the string.

REGEXP_LIKE(source, regexp, modes*)

SELECT 'true' FROM dual 
WHERE REGEXP_LIKE('Hello world', 'l{1,2}');

REGEXP_SUBSTR(source, regexp, position*, occurrence*, modes*)

SELECT REGEXP_SUBSTR('Hello World!', 'W([a-z]+)') FROM dual;

REGEXP_REPLACE(source, regexp, replacement*, position*, occurrence*, modes*)

SELECT REGEXP_REPLACE('Hello World!', 'W([a-z]+)') FROM dual;

REGEXP_INSTR(source, regexp, position*, occurrence*, return_option*, modes*)

SELECT REGEXP_INSTR('Hello World!', '([A-Z])', 1, 2, 0, 'c') FROM dual;

REGEXP_COUNT(source, regexp, position*, mode*) **

* optional parameter
** not available in Oracle 10g Express Edition

Thanks for all your comments.

Using regular expressions in Oracle SQL queries, pt. II

This is a second part of an article on regular expressions usage in Oracle. This part contains SQL examples only, for more details about functions and their parameters see first part of this article.

Regular expressions used in examples are very simple as this is no publication about regular expressions itself.

Using regular expressions in Oracle on actual tables

Let's say we have this simple table (users):

REGEXP_LIKE(source, regexp, modes*)

SELECT 
  name
FROM 
  users 
WHERE
  REGEXP_LIKE( city , 'M.+' );

Result:

name
----
Ivan Ivanovich
Juan Nadie

REGEXP_SUBSTR(source, regexp, position*, occurrence*, modes*)

SELECT
  DISTINCT REGEXP_SUBSTR ( email , '@([a-z]+)' ) 
FROM 
  users;

Result:

@abcxyz
@qwerty
@nadie

REGEXP_REPLACE(source, regexp, replacement*, position*, occurrence*, modes*)

SELECT
  REGEXP_REPLACE ( email , '@' , ' at ' ) 
FROM
  users;

j.doe at abcxyz.com
ivan at qwerty.ru
jane at abcxyz.com
juan at nadie.biz

REGEXP_INSTR(source, regexp, position*, occurrence*, return_option*, modes*)

SELECT
  id, login, name, city, email 
FROM
  users
WHERE
  REGEXP_INSTR ( email , '.' ) < REGEXP_INSTR ( email , '@' );

Result:

id	login	name	city			email
--	-----		--------	----------		----------------
1	jd		John Doe	Washington	j.doe@abcxyz.com

REGEXP_COUNT(source, regexp, position*, mode*)

SELECT
  login,
  REGEXP_COUNT( login , '[0-9]' ) AS num_count
FROM
  users;

Result:

login	num_count
-----		----
jd		0
ivan		0
jane84	2
jn2501	4