如何获得不同表中两个字段的总和？

Question

How to get the sum of Purchase_Order.QTY and Purchase_Request.QTY as balance? My problem is there are multiple po_number in Purchase_Order table with has a same counter.

Below is my Tables,

I need to get the total QTY of counter 100001 in purchase_order, so I can get the difference between QTY purchase_order and QTY purchase_request

Table Purchase_Order

counter | qty |

100001  | 10  |
100001  | 10  |
100001  | 10  |
100004  | 30  |

Table Purchase_Request

counter | total_qty |

100001  |     50    |
100002  |     100   |
100003  |     50    |
100004  |     70    |

And this my example OUTPUT

OUTPUT

counter | total_qty | balance |

100001  |     50    |  20     |
100002  |     100   |  100    |  
100003  |     50    |  50     |
100004  |     70    |  40     |

And this is my script,

<?php
$mysqli = new mysqli("localhost", "root", "", "test");

    $result = $mysqli->query("

    ");
    echo'<table id="tfhover" cellspacing="0" class="tablesorter" style="text-transform:uppercase;" border="1px">
        <thead>
        <tr>
        <th></th>
    <th>counter</th>
    <th>QTY</th>
    <th>balance</th>
        </tr>
        </thead>';
        echo'<tbody>';
    $i=1;   
while($row = $result->fetch_assoc()){
    echo'<tr>
            <td>'.$i++.'</td>
            <td>'.$row['counter'].'</td>
            <td>'.$row['total_qty'].'</td>
            <td>'.$row['balance'].'</td>
        </tr>';
       }
    echo "</tbody></table>";

?>

Help ?

Answer 1

SELECT PR.Counter,pr.qty-po.qty as remainingqty FROM Purchase_Request pr LEFT JOIN (Select counter,sum(qty) from Purchase_Order group by counter)po ON pr.Counter=po.Counter

Answer 2

Here is an option for you.

1. Get all records in Table Purchase_Order WHERE counter is = to Purchase_Request.counter
2. Loop through the results of QTY to get a sum
3. Compare the sum to QTY from the main table to determine if your order can be filled.

This is one option. Another suggestion would be to clean up your database. You might also be able to do SQL joins.

Answer 3

try this

select a.counter,a.po_number,a.unit_cost,sum(a.qty)-b.qty as ramaining_order_qty
    from table a
    inner join table b on a.counter=b.counter 
    group by a.counter,a.po_number,a.unit_cost,b.qty

Answer 4

You could join table 1 and 2 on counter number, then use sql to do the calculating

mysql_query("SELECT *, O.QTY - R.QTY AS difference FROM `Purchase_Order AS O LEFT OUTER JOIN Purchase_Request AS R ON O.counter = R.counter");

SELECT 
O.id, 
O.QTY,
COALESCE(O.QTY - (SELECT R.QTY 
                 FROM Purchase_Request AS R
                 WHERE O.counter = R.counter)) AS difference 
FROM Purchase_Order AS O;