What potential issues can arise when updating from MySQL 5.2 to 5.3 in PHP applications?

When updating from MySQL 5.2 to 5.3 in PHP applications, one potential issue that can arise is the deprecation of the `mysql_` functions in favor of `mysqli_` functions. To solve this issue, all instances of `mysql_` functions in the codebase need to be replaced with their `mysqli_` counterparts.

// Before updating
$result = mysql_query($query);

// After updating
$connection = mysqli_connect($host, $username, $password, $database);
$result = mysqli_query($connection, $query);