Getting a Sum and Count from Different Tables - mysql

Question

I'm guessing this is too local but I can't figure out a way to make it more general (which might be why I'm not able to find my answer on Google).
We have an application that tracks contacts for our business. These contacts (Contact table) are either contacted through the phone (Contact_Phone table) or through email (Contact_Email). If the user is contacted through the phone an agent keeps track of the total number of seconds (Contact_Phone.totalSeconds). Through a piece of business logic that I have no control over email contacts are treated as one second. A user might be contact through just email, just phone, or both.
I'm trying to generate a report on how long we've spent contacting each user but I can't get the results I expect.
Tables:
CREATE TABLE IF NOT EXISTS `Contact` (
`id` INT NOT NULL AUTO_INCREMENT ,
`name` VARCHAR(45) NULL ,
PRIMARY KEY (`id`) )
ENGINE = InnoDB;
CREATE TABLE IF NOT EXISTS `Contact_Email` (
`id` INT NOT NULL AUTO_INCREMENT ,
`ContactId` INT NULL ,
PRIMARY KEY (`id`) ,
INDEX `contact_email_contact_idx` (`ContactId` ASC) ,
CONSTRAINT `contact_email_contact`
FOREIGN KEY (`ContactId` )
REFERENCES `Contact` (`id` )
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
CREATE TABLE IF NOT EXISTS `Contact_Phone` (
`id` INT NOT NULL AUTO_INCREMENT ,
`totalSeconds` INT NULL ,
`ContactId` INT NULL ,
PRIMARY KEY (`id`) ,
INDEX `Contact_Phone_contact_idx` (`ContactId` ASC) ,
CONSTRAINT `Contact_Phone_contact`
FOREIGN KEY (`ContactId` )
REFERENCES `Contact` (`id` )
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
Test Data:
insert into Contact (id, name) values (1, 'Scott');
insert into Contact (id, name) values (2, 'Joe');
insert into Contact_Phone (totalSeconds, ContactId) values (10, 2);
insert into Contact_Phone (totalSeconds, ContactId) values (100, 2);
insert into Contact_Email (ContactId) values (1);
insert into Contact_Email (ContactId) values (1);
insert into Contact_Email (ContactId) values (2);
Query:
select
name,
(select sum(totalSeconds) from Contact_Phone where Contact_Phone.ContactId = Contact.id)
+
(select count(*) from Contact_Email where Contact_Email.ContactId = Contact.id)
from Contact;
Expected Results:
Joe 111
Scott 2
Actual Results:
Joe 111
Scott null
Thanks

Answer 1

How about using summaries and LEFT JOIN operations, like so?
SELECT Contact.name,
COALESCE(p.seconds,0) + COALESCE(e.seconds,0) seconds
FROM Contact.Name
LEFT JOIN (
SELECT ContactID AS id,
SUM(totalSeconds) AS seconds
FROM ContactPhone
GROUP BY ContactID
) p ON Contact.id = p.id
LEFT JOIN (
SELECT ContactID AS id,
COUNT(*) AS seconds
FROM ContactEmail
GROUP BY ContactID
) e ON Contact.id = e.id
The LEFT JOIN operations will preserve your result rows where one or the other of your "seconds" computations is NULL. And, the COALESCE operations will prevent your query from attempting arithmetic on NULL values, which yields NULL.