MySQL number of times string contains another string (count char appearance)

count_str.sql

CREATE FUNCTION COUNT_STR(haystack TEXT, needle VARCHAR(32))
  RETURNS INTEGER DETERMINISTIC
  BEGIN
    RETURN ROUND((CHAR_LENGTH(haystack) - CHAR_LENGTH(REPLACE(haystack, needle, ""))) / CHAR_LENGTH(needle));
  END;
  
  # Example: SELECT COUNT_STR('{"a":"test","fdfs":"test","more":"tests","b":"a"}',',"'); returns 3