Question

I have a table with a list of consignments for different users (table name is consignments). This table contains the consignment id (cons_id) as PK, the user_id and the date (and other details).

I have another table which contains the details of these consignments (table name is consignment). It has item_id as PK, cons_id as FK, the weight, tracking numbers and other details of the consignment. There are more than one entry in this table with the same foreign key which relates to a single entry in the first table (consignments).

I want to select all the entries in the first table (consignments) for a specific user, together with details obtained from the 2nd table (i.e. the total weight of all the items for a specific consignment, which are entries in the 2nd table, etc.).

I use the following mysql command:

SELECT a.cons_id, a.user_id, a.date, 
       sum(c.weight) AS weight, sum(c.weight*2) AS amount, 
       count(c.tracking) AS qty 
FROM   `consignments` AS a LEFT JOIN `consignment` AS c 
       ON c.cons_id = a.cons_id WHERE a.user_id = 103

This returns only the first item in the consignments table for that specific user and not the remainder of the entries. Off course, if I do not join it with the 2nd table, all the entries are returned.

I am not sure whether the aggregates like sum is the problem and how to do it correctly.

Any suggestion would be highly appreciated.

Answer 1

Use group by:

Example doing the weight (more sum() terms can be easily added):

SELECT a.cons_id, a.user_id, a.date, sum(c.weight) AS weight
FROM consignment a, consignments c where a.cons_id = c.cons_id 
GROUP BY a.cons_id,a.user_id, a.date;

Proof:

create table consignment ( cons_id integer, user_id integer, date timestamp );
create table consignments ( cons_id integer, item_id integer, weight integer );
insert into consignment values ( 1, 1, now());
insert into consignment values ( 2, 1, now());
insert into consignments values ( 1, 1, 10);
insert into consignments values ( 1, 2, 200);
insert into consignments values ( 2, 1, 12);
insert into consignments values ( 2, 2, 24);

Run the above query

 cons_id | user_id |            date            | weight 
---------+---------+----------------------------+--------
       2 |       1 | 2012-11-05 23:20:34.158361 |     36
       1 |       1 | 2012-11-05 23:20:25.535398 |    210