Automatically delete inactive users after 2 months

I am trying to modify this function:

// automatically delete users after 7 days in wordpress
function wcs_auto_delete_users() {
global $wpdb;
$query = $wpdb->prepare( "SELECT ID FROM $wpdb->users WHERE datediff( now(), user_registered ) > 7" );
if ( $oldUsers = $wpdb->get_results( $query, ARRAY_N ) ) {
    foreach ( $oldUsers as $user_id ) {
        wp_delete_user( $user_id[0] );
    }
}
}
add_action( 'wcs_daily_clean_database', 'wcs_auto_delete_users' );

wp_schedule_event( time(), 'daily', 'wcs_daily_clean_database' );

to work differently instead — I want it automatically delete users who haven’t been active in, say, 2 months. I have a plugin that tracks user activity and stores the data in wp_usermeta. Example:

user_id = 2; meta_key = wp_wp_kc_last_active_time; meta_value = 1422796627

This is the query that I’ve come up with:

SELECT user_id FROM wp_usermeta WHERE meta_key = 'wp_wp_kc_last_active_time' AND TIMESTAMPDIFF( second, now(), TIMESTAMP(SELECT meta_value) ) > 5184000

But it’s not selecting the right IDs. What should I change to make it work?

Your query is wrong because your third argument to TIMESTAMPDIFF is incorrect.

You should be using meta_value instead of SELECT meta_value.

SELECT user_id FROM wp_usermeta WHERE meta_key = 'wp_wp_kc_last_active_time' AND TIMESTAMPDIFF( second, now(), TIMESTAMP(meta_value) ) > 5184000;

Try that and see if the results start looking correct.

I just checked over the mySQL Date Function Docs and you appear to be doing this wrong.

Try the following instead:

SELECT user_id FROM wp_usermeta WHERE meta_key = 'wp_wp_kc_last_active_time' AND TIMESTAMPDIFF( MONTH, NOW(), FROM_UNIXTIME(meta_value) ) > 2;

Or Maybe…

global $wpdb;

$query = <<<SQL
 SELECT user_id 
 FROM {$wpdb->usermeta} 
 WHERE 
    meta_key = 'wp_wp_kc_last_active_time'
    AND DATEDIFF( NOW(), FROM_UNIXTIME( meta_value ) ) > 60
SQL;

$query = $wpdb->prepare( $query );

Which should gather the right users. If not, try it without the datediff statement and see if anything is returned. If not, then something is amiss with the meta_key (e.g. is it really wp_wp_… or just wp_kc_…)