更正此 CASE 表达式？

Question

I am receiving a syntax error for the following code.What am I doing wrong?

These are the series of questions.. I am on #4 (all others were executed correctly).

1. The marketing department wants to know if the Road-650 bicycle has more than 10 styles currently available. Using the Product table, create a statement using IF THEN logic to trigger on whether there are more or less than 10 of Road-650 bicycle units available. Submit the statement and the result of the query.

2. The marketing department has decided that it will only feature black colored Road-650 bicycles in the sales promotion. However, the marketing department may want to modify the sale at a later date. Use a DECLARE and SET statement to pre-set a variable color to "Black." Using the variable, run a query to show all the type of bicycles including all fields.

3. Building on the question two activity, add the "Quantity" and "ListPrice." Filter the results to only items in "Finished Goods Storage."

4. Building on the question three activity, the marketing department has decided that any products that currently have more than 100 units in stock will be discounted by 10%. All other products will have a 5% discount as part of the promotion. Create a CASE statement that modifies the "ListPrice" into a new field called "SalesPrice."

DECLARE @color varchar(20)
SET @color = 'black'

SELECT 
    Quantity, ListPrice,
    CASE
       IF Quantity > 100 THEN ListPrice - (ListPrice * .10)
       IF Quantity < 100 THEN ListPrice - (ListPRice * .05)
       ELSE NULL
    END AS SalesPrice
FROM 
    Production.Product
INNER JOIN
    Production.ProductInventory ON Production.ProductInventory.ProductID = Production.Product.ProductID
WHERE 
    color = @color 
    AND LocationID

ERROR:

Incorrect Syntax near the keyword 'IF'
Incorrect Syntax near the keyword 'THEN'
Incorrect syntax near the keyword 'THEN'

Answer 1

Change the IF to WHEN

CASE
WHEN Quantity > 100 THEN ListPrice - (ListPrice * .10)
WHEN Quantity < 100 THEN ListPrice - (ListPRice * .05)
ELSE NULL
END AS SalesPrice

Answer 2

Your case statement should look something like:

CASE
WHEN Quantity > 100 THEN ListPrice - (ListPrice * .10)
ELSE  ListPrice - (ListPRice * .05)
END AS SalesPrice

Keep in mind that your original statement didn't actually have a response for when the Quantity was EQUAL to 100, and would have returned NULL. I don't think that was desired behavior.