[Dbix-class] Join Three Tables With Aggregate Functions

[Trevor Leffler]

Hi Scott,

The cookbook has a section that should help you form subqueries in your 
search:

http://search.cpan.org/dist/DBIx-Class-0.08121/lib/DBIx/Class/Manual/Cookbook.pod#Correlated_subqueries

Note how a subquery can return a column max (or sum in your case) while 
referencing the outer search's table via its 'me' alias, which will get 
you your join.

Cheers,
--Trevor


On 10/05/2012 03:02 AM, scott at simpzoid.com wrote:
> Dear All,
>
> I have bit of SQL (mysql) which joins three tables to get all the records
> form the first table and sums from the 2 remaining tables.  The SQL looks
> like:
>
> select  t1.*, t2_total, t3_total from t1
> left join
> 	(select t1.id as t1_id, sum(t2.total) as t2_total from t1 left join t2 on
> t2.t1_id=t1.id group by t1.id) as t2s on t1.id = t2s.t1_id
> left join
> 	(select t1.id as t1_id, sum(t3.total) as t3_total from t1 left join t3 on
> t3.t1_id=t1.id group by t1.id) as t3s on t1.id = t3s.t1_id
> group by t1.id;
>
> This works fine.
>
> I reckon (obviously wrongly) that this translates to:
>
> my @join = $schema->resultset('T1')->search({
> 	},
> 	{
> 	    +select    =>   ['id' \['SUM(T2.total)'], \['SUM(T3.total)']],
> 	    as           =>   [qw /id t2_total t2_total/ ],
>              join         =>   ['T2', 'T3'],
> 	   group_by   =>   'id',
> });
>
> The search returns a resultset OK but the sums are multiplied by the
> number of permutations, e.g. SUM(T2.total) is a factor of 3 high if there
> 3 results in T3.
>
> I think the question I may be asking is what is the syntax to express a 3
> table join, on T1 to T2 and T1 to T3 type arrangement.
>
> Thanks,
> Scott
>
>
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