The problem

Uncaught Error: Call to undefined function mysql_connect()

why
In PHP 5+, you can use both mysql_connect() and mysqli_conncet() instead of mysqli_conncet().
The solution
In the PHPStudy environment, you can downgrade the PHP version by selecting the PHP5 + version.
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Web site – & gt; Management – & gt; PHP version. (You can choose to replace an older version of PHPStudy.)
If you want to use php7 without changing the code, you can use the admin ->; For PHP extensions, check the box before php_mysql.