Compiled PHP 7 missing mysql extension in WordPress

PHP 7 has removed mysql_* completely.

You need to use PDO or mysqli. Wordpress seems not to support this.

mysql_* functions got deleted in PHP 7.0 update your code to mysqli or PDO

Also take a look at prepared statements if you are handling user input. To reduce the chance of SQL injections

An example of mysqli connection string:

<?php
$mysqli = new mysqli("localhost", "user", "password", "database");
if ($mysqli->connect_errno) {
    echo "Failed to connect to MySQL: (" . $mysqli->connect_errno . ") " . $mysqli->connect_error;
}
?>

An example of pdo connection string:

<?php
    $dbh = new PDO('mysql:host=localhost;dbname=test', $user, $pass);
?> 

Note:

That mysqli example handles a connection error