Counting the number of occurrences of a substring within a string in PostgreSQL

Question

How can I count the number of occurrences of a substring within a string in PostgreSQL?

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Example:

I have a table

CREATE TABLE test.\"use         


        

Answer 1

Occcurence_Count = LENGTH(REPLACE(string_to_search,string_to_find,'~'))-LENGTH(REPLACE(string_to_search,string_to_find,''))

This solution is a bit cleaner than many that I have seen, especially with no divisor. You can turn this into a function or use within a Select.
No variables required. I use tilde as a replacement character, but any character that is not in the dataset will work.

Answer 2

Other way:

UPDATE test."user" SET result = length(regexp_replace(name, '[^o]', '', 'g'));

Answer 3

A common solution is based on this logic: replace the search string with an empty string and divide the difference between old and new length by the length of the search string

(CHAR_LENGTH(name) - CHAR_LENGTH(REPLACE(name, 'substring', ''))) 
/ CHAR_LENGTH('substring')

Hence:

UPDATE test."user"
SET result = 
    (CHAR_LENGTH(name) - CHAR_LENGTH(REPLACE(name, 'o', ''))) 
    / CHAR_LENGTH('o');

Answer 4

A Postgres'y way of doing this converts the string to an array and counts the length of the array (and then subtracts 1):

select array_length(string_to_array(name, 'o'), 1) - 1

Note that this works with longer substrings as well.

Hence:

update test."user"
    set result = array_length(string_to_array(name, 'o'), 1) - 1;

Answer 5

Return count of character,

 SELECT (LENGTH('1.1.1.1') - LENGTH(REPLACE('1.1.1.1','.',''))) AS count
--RETURN COUNT OF CHARACTER '.'