The $wpdb Object

Remarks#

There are two ways to reference the $wpdb object. The first is to use the PHP keyword global in order to act on the global instance of the object.

global $wpdb;
echo $wpdb->prefix;
// Outputs the prefix for the database

The second way to use the $wpdb object is to reference PHP’s $GLOBALS super global variable.

echo $GLOBALS['wpdb']->prefix;
// This will also output the prefix for the database

The second way is discouraged as it may not be considered the best practice.

Selecting a variable

In the most basic form, it is possible to select a single variable from a table by calling the object’s get_var method passing in an SQL query.

global $wpdb;
$user = $wpdb->get_var( "SELECT ID FROM $wpdb->users WHERE user_email='foo@bar.com'" );

It is very important to note that any untrusted values used in queries must be escaped in order to protect against attacks. This can be done using the object’s prepare method.

global $wpdb;
$email = $_POST['email'];
$user = $wpdb->get_var(
    $wpdb->prepare( "SELECT ID FROM $wpdb->users WHERE user_email=%s", $email )
);
if( !is_null( $user ){
    echo $user; 
} else {
    echo 'User not found';
}

Selecting multiple rows

You can use get_results to get multiple rows from database.

global $wpdb;
$userTable =$wpdb->prefix."users";

$selectUser = $wpdb->get_results("SELECT * FROM $userTable"); 

This will show all users list in array.