How to mysql query `$wpdb->get_var` `bp_groups` in buddypress?

I know that:

$wpdb->get_var("SELECT COUNT(*) FROM $wpdb->users;");

Can select wordpress user by mysql, but when I call a buddypress group, it failed, nothing returns

$wpdb->get_var("SELECT COUNT(*) FROM $wpdb->bp_groups;");

How do I fix this?

Solution

$wpdb only stores information on the Wordpress tables. Buddypress is going to be elsewhere.

The following page has a database map, with the default table names. Since the 'wp_' portion isn't certain you'll want to use $wpdb->prefix

So either of the following should work fine

$table = $wpdb->prefix."bp_groups";
$wpdb->get_var("SELECT COUNT(*) FROM $table;");

or inline

$wpdb->get_var("SELECT COUNT(*) FROM {$wpdb->prefix}bp_groups;");

You can use that schema map as a guide to getting more information, like how many users are in certain groups, etc...

Good luck :)