how to optimize?

[yuan]

//Calculate.php

class Calculate {
	var $student = array();

function Calculate($date) {
	global $sql;

	$data = $sql->query("SELECT `fund`.`student_ID`, `fund`.`student_name` FROM `fund`, `student` WHERE `fund`.`fund_date` <= '{$date}' AND `fund`.`student_ID` = `student`.`student_ID` GROUP BY `fund`.`student_ID` ORDER BY `fund`.`student_ID` ASC");
	if($sql->numrows($data) < 1)
		return;

	while($result = $sql->fetcharray($data)) {
		$id = $result['student_ID'];
		//get current date fund value			
		$data2 = $sql->query("SELECT SUM(`fund_value`) FROM `fund` WHERE `fund_date`='{$date}' AND `student_ID`='{$id}'");
		$cur = $sql->onedata($data2);

		//get previous date fund value;			
		$data3 = $sql->query("SELECT SUM(`fund_value`) FROM `fund` WHERE `fund_date`<'{$date}' AND `student_ID`='{$id}'");
		$prev = $sql->onedata($data3);

		$this->student[$id] = new Student($id, $result['student_name'], $cur, $prev);
	}
}
}

//Student.php
class Student {
	var $id, $name;
	var $cur = 0, $prev = 0;

function Student($id, $name, $cur, $prev) {
	$this->id = $id;
	$this->name = $name;
	$this->cur = $cur;
	$this->prev = $prev;
}
}

//BaseClass.php

class BaseClass extends Calculate {
	function BaseClass($date) {
		parent::Calculate($date);
		echo count($this->student);
		//print_r($this->student);
	}
}

//index.php

include_once('Student.php');
include_once('Calculate.php');
include_once('BaseClass.php');

$myBase = new BaseClass('2006-09-10');

Here are my learning class files. It can running successfully, but if my mysql results was too large. And it will waste a lot time to execute and print_r result cannot be show. Any expert can give me a guide??

my mysql table was like these

student table:
student_ID, student_name

fund table:
fund_ID, student_ID, fund_value, fund_date