MySQL：按两列分组并求和

Question

Building an inventory system. I have lots of products and each product has three different variables. So for stock totals I want to group by the two columns (product & size) and sum quantity to get stock total.

product	Size	Quantity
Widget one	2	275
Widget one	2	100
Widget two	3	150
Widget two	2	150

What I want for output:

product	Size	Quantity
Widget one	2	375
Widget two	3	150
Widget two	2	150

I figured out how to group by one column and sum using the code below:

$query = "SELECT product, SUM(Quantity) FROM inventory GROUP BY product";  
$result = mysql_query($query) or die(mysql_error());
// Print out result
while($row = mysql_fetch_array($result)){
    echo "Total ". $row['product']. " = ". $row['SUM(Quantity)'];
    echo "<br />";
}
?>

I am just stuck on grouping by both columns. Is it possible? or should I just create three different products for the of the three sizes and eliminate that column? Thanks.

Answer 1

Based on your example table, it appears you want to be grouping on product rather than id . You merely need to add the Size column to both the SELECT list and the GROUP BY

$query = "SELECT 
            product,
            Size, 
            SUM(Quantity) AS TotalQuantity 
          FROM inventory
          GROUP BY product, Size";

Note that I have added a column alias TotalQuantity , which will allow you to more easily retrieve the column from the fetched row via the more sensible $row['TotalQuantity'] , rather than $row['SUM(Quantity)']