Returns the substring that matches a regular expression within a string.
string (required): The string to search
pattern (required): The pattern to extract with.
position (optional): The index of the match to return.
NOTE: When the regular expression you want to use contains a slash, quotation or other special character, you will need to use a slash (/) to escape the special character. Regexp can vary based on the databases. Check the documentation of the database you use to find the correct syntax.