Query of attributes of mobile phone models, using several UNIONs to find distinct values I'd like to know if there's any room to improve the following query which is to find distinct values from multiple tables when someone searches for a model name. Two of the tables are storing phones' series attributes and model attributes. The model attr table is there to deal with special cases, like a series generally use black cases, but it also has released a special edition that uses golden cases.

Here's the query that I have come up. Basically I'm using UNION to unpivot table cpu and find distinct values across cpu,model_attr and series_attr Is there any need for improvement?

Here's a fiddle example.

Query:

SELECT attr_name,attr_val
FROM
(SELECT 'CPU_country' attr_name, c.country attr_val
 FROM cpu c INNER JOIN 
 series s ON s.cpu_id = c.cpu_id
 INNER JOIN model m ON m.series_id = s.series_id
 WHERE m.model_name RLIKE 'C79'
 UNION 

 SELECT 'CPU_hours' attr_name, c.hours attr_val
 FROM cpu c INNER JOIN 
 series s ON s.cpu_id = c.cpu_id
 INNER JOIN model m ON m.series_id = s.series_id
 WHERE m.model_name RLIKE 'C79'
UNION

SELECT a.attr_name attr_name,a.attr_value attr_val
FROM model m INNER JOIN
     series s
     on m.series_id = s.series_id LEFT JOIN
     series_attr sa
     ON sa.series_id = s.series_id LEFT JOIN
     attr saa
     on saa.attr_id = sa.attr_id LEFT JOIN
     model_attr ma
     ON ma.model_id = m.model_id LEFT JOIN
     attr a
     ON a.attr_id = ma.attr_id
     WHERE m.model_name RLIKE 'C79' AND a.attr_value IS NOT NULL
UNION 

SELECT saa.attr_name attr_name,saa.attr_value attr_val
FROM model m INNER JOIN
     series s
     on m.series_id = s.series_id LEFT JOIN
     series_attr sa
     ON sa.series_id = s.series_id LEFT JOIN
     attr saa
     on saa.attr_id = sa.attr_id LEFT JOIN
     model_attr ma
     ON ma.model_id = m.model_id LEFT JOIN
     attr a
     ON a.attr_id = ma.attr_id
     WHERE m.model_name RLIKE 'C79' AND saa.attr_value IS NOT NULL
 )k
GROUP BY attr_name,attr_val
ORDER BY attr_name


Table Schema (InnoDB):

CREATE TABLE series
    (`series_id` int, `series_name` varchar(20),`cpu_id` INT ,`ram`int)
;

INSERT INTO series
    (`series_id`,`series_name`,`cpu_id`,`ram`)
VALUES
    (1,'Nokia Series',1,512),
    (2,'Sony Series',2,1024)

;

CREATE TABLE model
    (`model_id` int, `model_name` varchar(20),`series_id` int)
;

INSERT INTO model
    (`model_id`,`model_name`,`series_id`)
VALUES
    (1,'A6578',1),
    (2, 'B2345',1),
    (3, 'C7906',2),
    (4, 'D3544',2)
;


CREATE TABLE attr
    (`attr_id` int, `attr_name` varchar(20),`attr_value` varchar(20))
;

INSERT INTO attr
    (`attr_id`,`attr_name`,`attr_value`)
VALUES
    (1, 'material','Gold'),
    (2, 'material','Plastic'),
    (3, 'color','Grey'),
    (4, 'color','Black'),
    (5, 'color','Green'),
    (6, 'color','White')

;

CREATE TABLE series_attr
    (`series_id` int, `attr_id` int )
;
INSERT INTO series_attr
    (`series_id`,`attr_id`)
VALUES
    (1,2),
    (1,5),
    (2,2),
    (2,3)
;



CREATE TABLE model_attr
    (`model_id` int, `attr_id` int)
;
INSERT INTO model_attr
    (`model_id`,`attr_id`)
VALUES
    (2,1),
    (2,4),
    (4,6)
;

CREATE TABLE cpu
    (`cpu_id` int,`cpu_name` varchar(20), `country` varchar(20),`hours`int,`frequency` int)
;
INSERT INTO cpu
    (`cpu_id`,`cpu_name`,`country`,`hours`,`frequency`)
VALUES
    (1,'CPU A','China',40,24000),
    (2,'CPU B','US',80,30000),
    (3,'CPU C','Japan',100,35000)
;
This is a pet peeve of mine, and others have disagreed with me about it, so please take it with a grain of salt. I really just can't stand single letter aliases. I mean, is cpu really so long that you can't just use the table name? Do you really need to shorten it to c? 

It's lazy and it's the worst kind of lazy. It's the kind of lazy that creates more work. Now, instead of plainly seeing series_attr.attr_name, I have to keep in my mind that saa means "series attribute attribute", and ma means "just plain model attribute" and a is a "model attribute attribute" and... Do you see where this is going? Imagine you're brand new to this code base. Would you be able to easily map the alias names to useful meanings? No. You wouldn't, but you shouldn't have to because alias names should be meaningful. 

That said, I do like that you've consistently formatted your code. I especially like that you put some whitespace around your UNION statements. However, I really prefer to see subqueries indented one level. It just makes it easier to follow the logic. 

You've also hardcoded C79 into your query. What if I want to find info on D82? I have to change the query in at least 4 places. You should be using a variable for this. Better yet, wrap the query in a stored procedure and use a parameter.