从数据库问题中提取2个十进制数

Question

$total_cost and $amount_paid value is 2028.36 as shown in the bottom right screenshot 
// values are from database. both are type decimal 15,2

$balance = ($total_cost - $amount_paid);

the result is 2.2737367544323E-13

结果应为0.我尝试将两者都转换为浮点数。仍然没有工作

查看下面的截图。我试着打印这个值，结果显示在右下角。

解决

我在数据库级别进行了计算。

$this->db->select('(SUM(ItemCost * OrderQty) - OrderAmountPaid) - Discount as Balance');