Question

在我的产品数据库中，我有一个价格和数量的列。我想要做的是将每行的价格和数量相乘，然后添加所有值，这样我就能得到我数据库中所有产品的总价格，这是我的代码：

产品型号：

public function getTotalAmountProducts()
{
   $this->db->select('sum(price*quantity) as stockvalue', FALSE);
    $query = $this->db->get('products');
   return $query->result();
}

控制器：

$this->data['totalamount'] = $this->products_model->getTotalAmountProducts();

它不起作用。请帮忙

Answer 1

应该是

public function getTotalAmountProducts()
{
  $this->db->select('price*quantity as stockvalue', FALSE);
  $query = $this->db->get('products');
  return $query->row()->stockvalue;
}

Answer 2

试试这个

library(plm)

#sample data
data("Wages", package = "plm")
#plm.data has been deprecated so instead use pdata.frame
Wag <- pdata.frame(Wages, index=595)

plm_model <- plm(lwage ~ black + ed + exp, data = Wag, index = c("id","time"), model="within")
summary(plm_model)

如何在sum函数中乘以2列

2 个答案: