SELECT CASE WHEN THEN (SELECT)

Question

I am trying to select a different set of results for a product depending on a product type. So if my product should be a book I want it to look up the UPC and Artist for a n

Answer 1

You Could try the other format for the case statement

CASE WHEN Product.type_id = 10
THEN
(
  Select Statement
)
ELSE
(
  Other select statement

)  
END
FROM Product 
WHERE Product.product_id = $pid

See http://msdn.microsoft.com/en-us/library/ms181765.aspx for more information.

Answer 2

For a start the first select has 6 columns and the second has 4 columns. Perhaps make both have the same number of columns (adding nulls?).

Answer 3

I ended up leaving the common properties from the SELECT queries and making a second SELECT query later on in the page. I used a php IF command to call for different scripts depending on the first SELECT query, the scripts contained the second SELECT query.

Answer 4

You should avoid using nested selects and I would go as far to say you should never use them in the actual select part of your statement. You will be running that select for each row that is returned. This is a really expensive operation. Rather use joins. It is much more readable and the performance is much better.

In your case the query below should help. Note the cases statement is still there, but now it is a simple compare operation.

select
    p.product_id,
    p.type_id,
    p.product_name,
    p.type,
    case p.type_id when 10 then (CONCAT_WS(' ' , first_name, middle_name, last_name )) else (null) end artistC
from
    Product p

    inner join Product_Type pt on
        pt.type_id = p.type_id

    left join Product_ArtistAuthor paa on
        paa.artist_id = p.artist_id
where
    p.product_id = $pid

I used a left join since I don't know the business logic.