1. 
PHP: mysql_free_result – Manual
www.php.net/manual/en/function.mysql-free-result.php
2.
5.4.26 mysql_free_result() – MySQL :: Developer Zone
dev.mysql.com/doc/c-api/8.0/en/mysql-free-result.html
3.
mysql_free_result – MariaDB Knowledge Base
mariadb.com/kb/en/mysql_free_result/
4.
PHP mysqli_free_result() Function – W3Schools
www.w3schools.com/PHP/func_mysqli_free_result.asp
5.
MySQL :: MySQL PHP API :: 6.5.25 mysql_free_result
dev.mysql.com/doc/apis-php/en/apis-php-function.mysql-free-result.html
6.
PHP mysql_free_result() Function – SinSiXX
w3schools.sinsixx.com/php/func_mysql_free_result.asp.htm
7.
c++ – when to call mysql_free_result (Resuing mysql_store …
stackoverflow.com/questions/16806704/when-to-call-mysql-free-result-resuing-mysql-store-result-mysql-res
8.
PHP: mysqli_result::free – Manual
www.php.net/manual/en/mysqli-result.free.php
9.
PHP mysql_free_result() 函数 – w3school
www.w3school.com.cn/php/func_mysql_free_result.asp
10.
wasted potential » How to fix Warning: mysql_free_result …
wastedpotential.com/how-to-fix-warning-mysql_free_result-supplied-argument-is-not-a-valid-mysql-result-resource/
11.
PHP mysqli_free_result() Function – Tutorialspoint
www.tutorialspoint.com/php/php_function_mysqli_free_result.htm
Conclusion
Guide above should be useful for Mysql_free_result.