mysql查询语法，从不同表中获取数据

Question

I got this bookshop website, and I'm trying to generate some statistics about sales. I've got two tables; books and sales_item . They look like this:

books

id  title
1   Cats
2   Dogs
3   Frogs

and sales_item

book_id  qty
1        2
2        2
3        4
3        1
2        1
and so on for hundreds of rows

So what I'm after is a sql query and a html table that tells me that we've sold 2 Cats, 3 Dogs and 5 Frogs. I want to match id from one table with book_id from the other and then add all the qty for each title . I have a feeling that this involves sql JOIN but I'm still not very comfortable with the syntax. Any help would be much appreciated.

Answer 1

select b.id, b.title, sum(s.qty) as NumSold 
from books b 
left outer join sales_item s on b.id = s.book_id 
group by b.id, b.title 
order by b.title

SQL Fiddle Example

Answer 2

select sum(qty), title
from sales_item s
left join books b on s.book_id = b.id
group by s.book_id

SQL Fiddle example

Answer 3

You can do this:

$query = ("select sum(qty) as 'Quantity', title from books b left join sales_item s on b.id = s.bookid' group by book_id");

$result = mysql_query($query);

//and this would be the code to print the html table

echo "<table border='1'>
<tr>
<th>Quantity</th>
<th>Pet</th>
</tr>";

while($row = mysql_fetch_array($result))
  {
  echo "<tr>";
  echo "<td>" . $row['Quantity'] . "</td>";
  echo "<td>" . $row['tittle'] . "</td>";
  echo "</tr>";
  }
echo "</table>";

Got help from a w3school example .