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PostgreSQL REGEXP_REPLACE

PostgreSQL REGEXP_REPLACE

Introduction to PostgreSQL REGEXP_REPLACE

The regular expression is a sequence of characters which is the short name for the list of strings. If any string is matching with any of the string which is the part of a list of the strings which are defined by the regular expression. PostgreSQL supports the regular expression and the function provided by PostgreSQL is used to replace substrings with a new substring that matches a POSIX regular expression. The PostgreSQL REGEXP_REPLACE() function is using a POSIX regular expression pattern.

Syntax:

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REGEXP_REPLACE(input_string, regex_pattern, replace_string,[, flags])

Explanation:

  1. input_string: This defines the input string which replacement should be taken place for a specified pattern which is a POSIX regular expression.
  2. regex_pattern: This defines the POSIX regular expression to match the string.
  3. flags: This flag is used to control the behavior of the REGEXP_REPLACE() function, This can have the value of one or more characters.
  4. Replace_string: This string defines a string that replaces the substring which matches the POSIX regular expression pattern.

Examples of PostgreSQL REGEXP_REPLACE

Here are the following examples to implement the PostgreSQL REGEXP_REPLACE function

Example #1 – Example to arrange the name

Consider the following name format like the first name and then last name:

‘Jacob David’

Now suppose we want to re-arrange the last name and the first name for some of the purposes like the last name and then the first name. So, we can use the PostgreSQL REGEXP_REPLACE() function to do this as follows:

SELECT REGEXP_REPLACE('Jacob David',
'(.*) (.*)',
'\2, \1');

Illustrate the result of the above statement by using the following snapshot.

PostgreSQL REGEXP_REPLACE 1

Example #2

Example to remove the string, consider we have a string in following as follows:

“xyz54321ABC”

Now, we will remove all alphabets characters from the above string by using the following statement:

SELECT REGEXP_REPLACE('xyz54321ABC',
'[[:alpha:]]',
'',
'g');

Illustrate the result of the above statement by using the following snapshot.

PostgreSQL REGEXP_REPLACE 2

Now, we will remove all digits from the above string by using the following statement:

SELECT REGEXP_REPLACE('xyz54321ABC',
'[[:digit:]]',
'',
'g');

Illustrate the result of the above statement by using the following snapshot.

PostgreSQL REGEXP_REPLACE 3

In the above examples, we have used the following regular expressions.

'[[:alpha:]]'

and

'[[:digit:]]'

Also, we have used the replacement string as ‘’ and the flag ‘g’ we have used to instruct the PostgreSQL REGEXP_REPLACE function to replace all of the occurrences of the matched string and not the just first occurrence.

Example #3

Remove multiple occurrences of the spaces. Consider the following example which removes more than one space that occurred in a string. Consider the following statement to do the same. 

SELECT REGEXP_REPLACE('PostgreSQL  is    awesome   database',
'( ){2,}',
' ',
'g');

Illustrate the result of the above statement by using the following snapshot.

Output 4

Example #4

We will create a table named ‘student’ by using the CREATE TABLE statement as follows:

create table student
(
stud_id serial PRIMARY KEY,
stud_fname VARCHAR(80) NOT NULL,
stud_lname VARCHAR(80) NOT NULL
);

Now, we will insert some data into the student table by using the INSERT INTO statement as follows

INSERT INTO student(stud_fname,stud_lname)
VALUES
('Smith','Johnson'),
('Williams','Jones'),
('Brown','Davis');

Illustrate the result of the above INSERT statement by using the following SQL statement and snapshot.

select * from student;

Output 5

Consider the following SQL statement where we are checking whether the stud_lname is having ‘Jo’ substring and if it exists then we are replacing it with ‘K’

SELECT REGEXP_REPLACE(stud_lname , 'Jo', 'K') AS "New Name"
FROM student;

Illustrate the result of the above SQL statement by using the following snapshot.

Output 6

Also, consider the other example,

Consider the following SQL statement where we are checking whether the stud_lname is having ‘s’ substring and if it exists then we are replacing it with ‘K’

SELECT REGEXP_REPLACE(stud_lname , 's', 'K') AS "New Name"
FROM student;

Illustrate the result of the above SQL statement by using the following snapshot.

 Output 7

Advantages of using PostgreSQL REGEXP_REPLACE () function

1. The PostgreSQL REGEXP_REPLACE () function supports various flags,

Consider examples like:

  • flag ‘i’ : match case-insensitively
  • flag ‘g’: search globally for each occurrence.

2. The PostgreSQL REGEXP_REPLACE() replaces all occurrences of the substring by the new string.

3. We can use The PostgreSQL REGEXP_REPLACE() function the substring in variable length or dynamic strings.

Conclusion

We hope from the above article you have understood how to use the PostgreSQL REGEXP_REPLACE() function and how the PostgreSQL REGEXP_REPLACE() function works. Also, we have added several examples of the PostgreSQL REGEXP_REPLACE() function to understand it in detail.

Recommended articles

This is a guide to PostgreSQL REGEXP_REPLACE. Here we discuss the examples to implement the PostgreSQL REGEXP_REPLACE function along with the Advantages. You may also look at the following articles to learn more –

  1. SQL Administration
  2. PostgreSQL List Users
  3. MySQL Constraints
  4. MySQL Self Join
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