MySQL - Getting summary of multiple grouped rows? - sql

Question

2 tables: owners & cars
An owner can have many cars. A car can be marked as usable_offroad, usable_onroad, or both. The cars table has usable offroad and usable_onroad fields which can be set to 0 or 1 (no or yes)
Consider the following query:
SELECT *
FROM owners
LEFT JOIN cars on cars.owner_id = owners.id
GROUP BY owners.id
ORDER BY owners.last_name
My goal is to return a list of owners, and whether or not each owns a an onroad or offroad vehicle, or both:
Last Name First Name Has Offroad Car Has Onroad Car
----------------------------------------------------------------------
Smith Todd Yes No
Smith Tom Yes Yes
Test Sue No Yes
Thumb Joe No No
White Al Yes No
How do I query this? Was thinking of using ROLLUP, but would prefer if the summary wasn't an appended row but an actual field on the already grouped owner row instead.

Answer 1

Use:
SELECT DISTINCT
o.lastname,
o.firstname,
CASE WHEN COALESCE(y.num_offroad, 0) > 0 THEN 'yes' ELSE 'no' END AS "Has Offroad Car"
CASE WHEN COALESCE(x.num_onroad, 0) > 0 THEN 'yes' ELSE 'no' END AS "Has Onroad Car"
FROM OWNERS o
LEFT JOIN (SELECT c.owner_id,
COUNT(*) AS num_onroad
FROM CARS c
WHERE c.usable_onroad = 1
GROUP BY c.owner_id) x ON x.owner_id = o.id
LEFT JOIN (SELECT c.owner_id,
COUNT(*) AS num_offroad
FROM CARS c
WHERE c.usable_offroad = 1
GROUP BY c.owner_id) y ON y.owner_id = o.id

Answer 2

Try this:
SELECT
T1.lastname,
T1.firstname,
T1.id in (SELECT owner_id FROM cars WHERE usable_offroad) AS `Has Offroad Car`,
T1.id in (SELECT owner_id FROM cars WHERE usable_onroad) AS `Has Onroad Car`
FROM owners T1
ORDER BY T1.lastname, T1.firstname
Results:
'Smith', 'Todd', 1, 0
'Smith', 'Tom', 1, 1
'Test', 'Sue', 0, 1
'Thumb', 'Joe', 0, 0
'White', 'Al', 1, 0
Here's my test data:
CREATE TABLE owners (id INT NOT NULL, firstname NVARCHAR(100) NOT NULL, lastname NVARCHAR(100) NOT NULL);
INSERT INTO owners (id, firstname, lastname) VALUES
(1, 'Todd', 'Smith'),
(2, 'Tom', 'Smith'),
(3, 'Sue', 'Test'),
(4, 'Joe', 'Thumb'),
(5, 'Al', 'White');
CREATE TABLE cars (id INT NOT NULL, owner_id INT NOT NULL, usable_onroad INT NOT NULL, usable_offroad INT NOT NULL);
INSERT INTO cars (id, owner_id, usable_offroad, usable_onroad) VALUES
(1, 1, 1, 0),
(2, 2, 1, 0),
(3, 2, 0, 1),
(4, 3, 0, 1),
(5, 3, 0, 1),
(6, 5, 1, 0);

Answer 3

Using a sub-query to sum all the flags, and then checking if one is > 1 should do the job:
SELECT last_name, first_name,
CASE WHEN usable_offroad_count > 0 THEN 'Yes' ELSE 'No' END has_offroad_car,
CASE WHEN usable_onroad_count > 0 THEN 'Yes' ELSE 'No' END has_onroad_car
FROM (
SELECT owners.last_name, owners.first_name,
SUM( cars.usable_offroad ) usable_offroad_count,
SUM( cars.usable_onroad ) usable_onroad_count
FROM owners
LEFT JOIN cars on cars.owner_id = owners.id
GROUP BY owners.id
)
ORDER BY last_name

Answer 4

SELECT * ,
if ( cars.usable offroad = 1 and usable_onroad= 1 , 'Both'
, if( cars.usable offroad = 1 and usable_onroad= 0 , 'Offroad' , 'Onroad')
) as Status
FROM owners
LEFT JOIN cars on cars.owner_id = owners.id
GROUP BY owners.id
ORDER BY owners.last_name