I have since switched over to using native mysql stored functions for this

drop function if exists `urldecode`;

DELIMITER $$

CREATE FUNCTION urldecode(encoded_url VARBINARY(255))
RETURNS VARCHAR(255)
DETERMINISTIC
BEGIN
    DECLARE decoded_url VARBINARY(255);
    DECLARE char_code INT;
    DECLARE i INT;
    DECLARE encoded_char CHAR(3);

    SET decoded_url = REPLACE(encoded_url, '+', ' ');
    SET i = LOCATE('%', decoded_url);

    WHILE i > 0 DO
        SET encoded_char = SUBSTRING(decoded_url, i + 1, 2);
        SET char_code = CONV(encoded_char, 16, 10);
        SET decoded_url = INSERT(decoded_url, i, 3, CHAR(char_code));
        SET i = LOCATE('%', decoded_url, i + 1);
    END WHILE;

    RETURN convert(decoded_url using utf8mb4);
END$$

DELIMITER ;

select urldecode('cgo+uint32+to+pointer'),
urldecode('Na%C3%AFvet%C3%A9');

drop function if exists `get_url_param`;

DELIMITER $$

CREATE FUNCTION get_url_param(url_string TEXT, param_name VARCHAR(255))
RETURNS VARCHAR(255)
DETERMINISTIC
BEGIN
    DECLARE start_index INT;
    DECLARE end_index INT;
    DECLARE param_value VARCHAR(255);

    SET url_string = SUBSTRING(url_string, LOCATE('?', url_string) + 1);
    SET param_name = CONCAT(param_name, '=');
    SET start_index = LOCATE(param_name, url_string);

    IF start_index = 0 THEN
        RETURN NULL;
    END IF;

    SET start_index = start_index + CHAR_LENGTH(param_name);
    SET end_index = LOCATE('&', url_string, start_index);

    IF end_index = 0 THEN
        SET end_index = CHAR_LENGTH(url_string) + 1;
    END IF;

    SET param_value = SUBSTRING(url_string, start_index, end_index - start_index);
    RETURN `urldecode`(param_value);
END$$

DELIMITER ;

select
`get_url_param`('https://www.youtube.com/watch?v=KDszSrddGBc','v'),-- "KDszSrddGBc"
`get_url_param`('watch?v=KDszSrddGBc','v'),-- "KDszSrddGBc"
`get_url_param`('watch?v=KDszSrddGBc','x'),-- null
`get_url_param`('https://www.google.com/search?q=cgo+uint32+to+pointer&rlz=1C1CHBF_enUS767US767&oq=cgo+uint32+to+pointer&aqs=chrome..69i57.12106j0j7&sourceid=chrome&ie=UTF-8','q'),-- "cgo uint32 to pointer"
`get_url_param`('/search?q=Na%C3%AFvet%C3%A9&oq=Na%C3%AFvet%C3%A9','q')-- "Naïveté"

---

MySQL get_url_param

This is the first MySQL UDF I've seen that can actually user arguments and that is written in Go. So besides this UDF's specific task of parsing URL parameters, this will make an excellent example for making new UDF's with Go in the future.

Go is exceptionally powerful and fairly simple language to understand and write in, with a good community behind it and a strong built in library. It also can be used directly with C programs, which it made it sound perfect for creating MySQL UDF's with way more ease than using pure C.

I mean here I am, a lowley PHP dev, and now my MySQL instances have the power to extract URL parameters with perfection.

Installation instructions

These are the Linux instructions, so but I'm sure the standard, say Windows, instructions can be adapted to work with the Go steps of compiling and installing the plugin.

1. make sure libmysqlclient-dev is installed apt install libmysqlclient-dev
2. Find your MySQL plugins dir, which is likely "/usr/lib/mysql/plugin" (or you can find it by running select @@plugin_dir; on your MySQL server)
3. Navigate to the folder where you cloned this repository to, and run the following (replacing the plugin path with your own) go build -buildmode=c-shared -o get_url_param.so && cp get_url_param.so /usr/lib/mysql/plugin/get_url_param.so
4. Then on your MySQL server, run this to declare the function in your current schema create function`get_url_param`returns string soname'get_url_param.so';

Usage

string get_url_param ( string url , string parameter )

Parameters

url - The URL containing the query string (URL doesn't need to be complete, e.g. can start with "http://...", or "/...", etc.) parameter - The name of the parameter to have its value returned

Return values

This function will always return a string if the parameter exists, even its value is empty. Otherwise, if the parameter does not exist, this function will return null.

If a string is returned, it is URL decoded, including plus signs (+), so %20 and + in a parameter both will be converted to . This also fully supports UTF8 (and likely many other character sets, considering it's using the built-in Go URL parser).

Examples

select`get_url_param`('https://www.youtube.com/watch?v=KDszSrddGBc','v');
-- "KDszSrddGBc"

select`get_url_param`('watch?v=KDszSrddGBc','v');
-- "KDszSrddGBc"

select`get_url_param`('watch?v=KDszSrddGBc','x');
-- null

select`get_url_param`('https://www.google.com/search?q=cgo+uint32+to+pointer&rlz=1C1CHBF_enUS767US767&oq=cgo+uint32+to+pointer&aqs=chrome..69i57.12106j0j7&sourceid=chrome&ie=UTF-8','q');
-- "cgo uint32 to pointer"

select`get_url_param`('/search?q=Na%C3%AFvet%C3%A9&oq=Na%C3%AFvet%C3%A9','q');
-- "Naïveté"