MYSQL: JOIN makes SUM double

This should be really easy. Believe me,开发者_如何转开发 I've been researching this for hours. My query:

SELECT not_piece.pid, part.name AS 'Part Name', SUM(qty_left) AS 'In Stock'
FROM not_piece 
JOIN part ON not_piece.pid = part.pid 
GROUP BY part.name;

Only two tables, not_piece and part.

select qty_left 
from not_piece 
where pid='M-MP-007r8'; 

returns 5.

Since the part.name appears twice in the parts table (that's fine), the sum is 10, not 5.

How do I make this join without doubling the sum?

Thanks.

SELECT t.pid, p.name AS 'Part Name', t.InStock AS 'In Stock'
    FROM (SELECT pid, SUM(qty_left) AS InStock
              FROM not_piece
              GROUP BY pid) t
        INNER JOIN part p
            ON t.pid = p.pid

With your GROUP BY, try grouping by your primary key, pid:

SELECT not_piece.pid, part.name AS 'Part Name', SUM(qty_left) AS 'In Stock'
FROM not_piece 
JOIN part ON not_piece.pid = part.pid 
GROUP BY part.pid;