使用INNER JOIN从3个相关表中获取数据

Question

I want to get sum of the prices and items columns which are related to 3 tables.I am trying with INNER JOIN in the following script. It only displays 1 invoice total. And else statement is not displaying 0 When data is 0.

function TotalRecord($total){
global $db;
$date = date("Y-m-d");
     $query = $db->prepare("SELECT sum(a.prices), sum(a.item) FROM items a INNER 
    JOIN invoice_items b ON a.item_id = b.item_id INNER JOIN invoices c ON 
    b.invoiceId = c.invoiceId  WHERE c.invoice_date = :date ");
    $query->bindParam(':date', $date);
    $query->execute();
    for($i=0; 
             $rows = $query->fetch(); 
    $i++){
         $totalPrice = $rows['sum(a.prices)'];
         $totalitems = $rows['sum(a.item)'];
         $array = array('total' => $totalPrice , 'items' => $totalitems );

        if(count($array) > 0)
        {
            echo $array[$total];
        }
        else
        {
            echo "0";
        }

    }
}

Answer 1

If you have multiple SUM function, you should probably use the GROUP BY instruction. See below https://www.w3schools.com/sql/sql_groupby.asp
https://www.w3resource.com/sql/aggregate-functions/sum-with-group-by.php

Answer 2

try this

 SELECT sum(a.prices), sum(a.item) FROM (items a INNER 
JOIN invoice_items b ON a.item_id = b.item_id INNER JOIN invoices c ON 
b.invoiceId = c.invoiceId )  group by  b.item_id,b.invoiceid WHERE c.invoice_date = :date