MySQL, conditionally adding columns - mysql

Question

I have two tables, the first holds data about patients, it looks like this.
id patient sex impact
------------------------------------------
1 Bill Jones male .1
2 Sarah Smith female .4
The second holds "multipliers". These multipliers will be used to multiply the impact in the table above.
id type type_value multiplier
-----------------------------------------------
1 patient Bill Jones .5
2 sex male .3
3 sex male .8
4 sex female .7
I am trying to run a query that will return the following:
patient patient_total sex_total new_impact
-------------------------------------------------------------------------------
Bill Jones .5 1.1 .16
Sarah Smith 0 .7 .28
Where the new impact is the (patient_total + sex_total) * impact for each patient.
Here are the create statements:
--
-- Table structure for table `impact`
--
CREATE TABLE IF NOT EXISTS `impact` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`patient` varchar(20) NOT NULL,
`sex` varchar(7) NOT NULL,
`impact` float NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=3 ;
--
-- Dumping data for table `impact`
--
INSERT INTO `impact` (`id`, `patient`, `sex`, `impact`) VALUES
(1, 'Bill Jones', 'male', 0.1),
(2, 'Sarah Smith', 'female', 0.4);
--
-- Table structure for table `multipliers`
--
CREATE TABLE IF NOT EXISTS `multipliers` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`type` varchar(20) NOT NULL,
`type_value` varchar(60) NOT NULL,
`multiplier` float NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=14 ;
--
-- Dumping data for table `multipliers`
--
INSERT INTO `multipliers` (`id`, `type`, `type_value`, `multiplier`) VALUES
(1, 'patient', 'Bill Jones', 0.5),
(2, 'sex', 'male', 0.3),
(3, 'sex', 'male', 0.8),
(13, 'sex', 'female', 0.7);
I have tried several iterations of the following query, but can't get it to work :/
Updated quer - working for sex_total column, not for patient_total column :/
select p.patient, ifnull(sum(ipatient.multiplier), 0) as patient_total, ifnull(sum(isex.multiplier), 0) as sex_total, (ifnull(sum(ipatient.multiplier), 0) + ifnull(sum(isex.multiplier), 0) * p.impact) as new_impact
from impact p
left outer join multipliers ipatient
on ipatient.type = 'patient' and ipatient.type_value = p.patient
left outer join multipliers isex
on isex.type = 'sex' and isex.type_value = p.sex
group by p.patient
Could someone please help?
Thanks

Answer 1

You just need to join in the impact rows and then aggregate the results. The following does two joins, one for each type of impact:
select p.patient, sum(ipatient.multiplier) as patient_total,
sum(isex.multiplier) as sex_total,
(sum(ipatient.multiplier) * sum(isex.multiplier) * p.imact
) as new_impact
from impact p left outer join
multipliers ipatient
on ipatient.type = 'patient' and ipatient.type_value = p.patient left outer join
multipliers isex
on isex.type = 'sex' and isex.type_value = p.sex
group by p.patient;
You might need a coalesce() if there might be some rows that have no matches for either the patient name or sex.
EDIT:
Dumb. Dumb. Dumb. The above fails because the isex multiplies the rows, so it affects the sum() of ipatient. This version works:
select p.patient,
sum(case when m.type = 'patient' then m.multiplier else 0 end) as patient_total,
sum(case when m.type = 'sex' then m.multiplier else 0 end) as sex_total,
(sum(m.multiplier)* p.impact
) as new_impact
from impact p left outer join
multipliers m
on m.type = 'patient' and m.type_value = p.patient or
m.type = 'sex' and m.type_value = p.sex
group by p.patient;
You can see it here.
If you don't like all the decimal places from the float, you can switch to a numeric/decimal data type.

Answer 2

This query will give you the columns you need, but you'll have to do the multiplication yourself.
SELECT i.id, i.patient, i.impact,
(SELECT IFNULL(SUM(multiplier), 0) FROM multipliers
WHERE type='patient' AND type_value=i.patient) `patient_total`,
(SELECT IFNULL(SUM(multiplier), 0) FROM multipliers
WHERE type='sex' AND type_value=i.sex) `sex_total`
FROM impact i