如何在这个特定情况下从2D数组中检索数据？

I have a array with this var_dump value:

$query = $wpdb->get_results("SELECT COUNT(*) FROM `$table` WHERE my mysql conditions"); 

var_dump($query); is this:

array(1) { [0]=> object(stdClass)#414 (1) { ["COUNT(*)"]=> string(3) "494" } } 

How can I get the number 494 inside a variable?

$number = $query[0];

It'd be cleaner if you aliased your count so:

SELECT COUNT(*) AS `count`

then

$number = $query[0]->count;

If you only need to retrieve a single value, use $wpdb->get_var() instead of get_results(). This method exists specifically for situations like yours.

$number = $wpdb->get_var("SELECT COUNT(*) FROM `$table` WHERE my mysql conditions");