MYSQL查询将列名匹配到另一个表中的行

Question

I have two tables in MYSQL, one contain a list of options a customer can pick from and the other has the cost of the options. I would like a view that returns the cost of each customers option set. For my example I'll use the analogy of buying a new car.

Customers table

customer - sunroof - mag_wheels - spoiler 
--------------------------------------------------
John     - true    - true       - false 
Steve    - false   - true       - false
Lucy     - false   - false      - false

Options table

option      - price
-----------------
sunroof     - 100
mag_wheels  - 150
spoiler     -  75

Desired results

customer   - cost
-----------------
John       - 250
Steve      - 150
Lucy       - 0

or this would do, as I good easily multiply selected by price and then group by customer

customer   - option     - selected - price
------------------------------------------
John       - sunroof    - true     - 100
John       - mag_wheels - true     - 150
John       - spoiler    - false    -  75
Steve      - sunroof    - false    - 100
Steve      - mag_wheels - true     - 150
Steve      - spoiler    - false    -  75
Lucy       - sunroof    - false    - 100
Lucy       - mag_wheels - false    - 150
Lucy       - spoiler    - false    -  75

I've been puzzling over this for hours now and I can't even figure out where to start, a join seems out of the question as there are no common elements to match. I wonder if using UNION is the answer but I can't figure out how to combine row values with column headings.

If anyone could point me in the right direction I'd be ever so grateful, double points if you come up with a solution that dynamically picks up the different options so I could add more in the future without rewriting the query.

Many thanks in advance.

The reason I wanted to have all the options as a single row is I was hoping to use Access to make a form for picking the options and I couldn't figure out how a single form could create multiple rows.

Answer 1

This is a horrible data layout. You should have an association table, with one row per customer and option.

But, you can do it:

select c.customer, sum(o.cost) as cost
from customers c left outer join
     options o
     on (c.sunroof = true and o.option = 'sunroof' or
         c.mag_wheels = true and o.option = 'mag_wheels' or
         c.spoiler = true and o.option = 'spoiler'
        )
group by c.customer;

EDIT:

You do not want all options in a single record. Instead, you need an association table:

create table customer_options (
    customer_optionid unsigned auto_increment,
    customer varchar(255) references customer(name),
    option varchar(255) references option(option)
);

Actually you should really have integer primary keys for all the tables, and use them for the foreign key references. If you need data in the output in the question, then just write a query to return it in that format.

Answer 2

Looking at the table structure, even I think it will not be possible to write joins because as you mentioned, the table structure doesn't have a relation between them.

I am assume you have just started the project, so it's time you first re-visit your DB structure and correct it.

Ideally, you should have a customer table with a customer id. Then you should have products table with product id. One table which will have data on what products customers have purchased - something like customer_products. This will be a one to many relation. So customer 1 can have product 1,3 and 5. Which would means in customer_product there will be three entries.

And then when you want to do a sum total, you can first join the table customer, product based on customer_product and then do a sum of the price also to get the total amount for individual customer.

Answer 3

Bad design. You must a have a customers table like this:

custumer_id
customer_name
other fileds...

On the other hand you should have an accesories table, where you usually describe each item-

accesory_id
accesory_name
supplier_id
country_of_origin
other stuff

Also an accesory_price table, where prices are added due the fact that prices change.

accesory_id
price
active_price
date_price_added

An finally you should relate all in a customer_accesory table:

customer_id
accesory_id

By having this, you can join tables and select both customer basket size and customer preferences of accesories. Basket size, or the amount purchased by each customer can be summarized SUM , AVG , COUNT or you can pivot data using GROUP_CONCAT in order to generate high quality reports.