Error reporting when upgrading PHP version 5.6 to 7. X under WordPress (resolved)

Cause of event:

When using WordPress, the theme needs to be upgraded. The PHP version required for viewing the theme is 7.1+

When the website is not backed up, the PHP version is changed to 7.2, which directly leads to the website error

Fatal error: Uncaught Error: Call to undefined function mysql_ connect()

Check many online tutorials, which are MySQL in wp-db.php_Change connect() to mysqli_Connect(), no result

At first, I thought that the database reported an error, checked the database in detail, wrote checkdb.php, locally connected to the database, and checked that the database server was running well

Solution:

Set define ('wp_use_ext_mysql ', true) in wp-config.php delete

error explanation:

define('WP_USE_EXT_MYSQL',true);

define(‘WP_USE_EXT_MYSQL’, true); Force WP to use MySQL by default instead of MySQL Li
so please delete this line and the problem should be solved.

Otherwise, you can check nd in the PHP 7 configuration_Mysqli extension, and disable mysqli extension – > Select the PHP version.