查询中变量列名的php语法

Question

I am trying to pass the name of a column as a variable to a PHP database query.

the hard coded syntax works perfectly and is: select max([257612cr]) as price from Price_TekwaniPrice where customeraccount='DAY001'

When I pass the variable I get error trying to get property ofnon object. my syntax is:

        $query = $this->db->query("
select max(['$product']) as price from Price where customeraccount='$customer'
      ");

I also tried:

        $query = $this->db->query("
select max(".$product.") as price from Price where customeraccount='$customer'
      ");

I have confirmed that the variables are being passed correctly. the syntax for '$customer' works perfectly so just passing the $product variable as a column name is proving cumbersome.

I am using php with codeigniter. any advice welcome.

Thanks as always,

Answer 1

No need to concatenate a php variable when already opened double quotes try this

 $query = $this->db->query("
select max([$product]) as price from Price where customeraccount='$customer'
      ");

or

$query = $this->db->query("
select max($product) as price from Price where customeraccount='$customer'
      ");

While about the error you are getting is due i think your database driver is not loaded first try to load database

$this->load->database('default', TRUE);

The best way to use CI's Active record you can do so

$this->db->select_max($product);
$this->db->where('customeraccount', $customer); 
$query = $this->db->get('Price');

See Active Record