Source

File: wp-includes/class-wp-user-query.php

protected function get_search_sql( $string, $cols, $wild = false ) {
		global $wpdb;

		$searches      = array();
		$leading_wild  = ( 'leading' === $wild || 'both' === $wild ) ? '%' : '';
		$trailing_wild = ( 'trailing' === $wild || 'both' === $wild ) ? '%' : '';
		$like          = $leading_wild . $wpdb->esc_like( $string ) . $trailing_wild;

		foreach ( $cols as $col ) {
			if ( 'ID' === $col ) {
				$searches[] = $wpdb->prepare( "$col = %s", $string );
			} else {
				$searches[] = $wpdb->prepare( "$col LIKE %s", $like );
			}
		}

		return ' AND (' . implode( ' OR ', $searches ) . ')';
	}