Why do we need the line require_once(ABSPATH. 'wp-admin/includes/upgrade.php'); when updating wordpress sql table?

Question

WordPress

Hi
Why is this line in a piece of code
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function update_table( ) {
global $wpdb;

require_once(ABSPATH . 'wp-admin/includes/upgrade.php');

$table_name = $wpdb->get_blog_prefix() . 'test_table';
$charset_collate = "DEFAULT CHARACTER SET {$wpdb->charset} COLLATE {$wpdb->collate}";

$sql = "CREATE TABLE {$table_name} (
id bigint(20) unsigned NOT NULL auto_increment,
address varchar(255) NOT NULL default '',
alert varchar(20) NOT NULL default '',
meta longtext NOT NULL default '' ,
new_meta longtext NOT NULL default '',
PRIMARY KEY (id),
{$charset_collate};";

dbDelta($sql);
}

update_table();