Adding a Custom table in WordPress using a WordPress plugin.

gistfile1.php

<?php

function wpct_create_db_table() {

global $wpdb;
	
	/* create the table name using the wordpress table prefix for this site */
	$wpct_tablename = $wpdb->prefix . "wpct";
	
	/* setup the structure of the table creating these as a variable */
	$wpct_sql = "CREATE TABLE IF NOT EXISTS $wpct_tablename (
		wpct_id int(11) NOT NULL AUTO_INCREMENT,
		wpct_post_id varchar(100) NOT NULL,
		wpct_user_id varchar(100) NOT NULL,
		wpct_username varchar(100) NOT NULL,
		wpct_date datetime,
		wpct_ip varchar(100) NOT NULL,
		PRIMARY KEY  (wpct_id)
	);";
	
	/* include dbdelta stuff */
	require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
	
	/* build the table using the variables above */
	dbDelta( $wpct_sql );

}

/* run the table creation function only on plugin activation */
register_activation_hook( __FILE__, 'wpct_create_db_table' );

?>