Q:

CASE Syntax error when > is used in the WHEN clause

This Query runs fine when I do not have the ">" symbol in the WHEN clause however I need this to work when the ProposalDate is any date later than '2017-04-10 00:00:00.000'. Not sure why I am getting a Syntax error when I add the > into the WHEN clause.
SELECT *,
    CASE ProposalDate WHEN > '2017-04-10 00:00:00.000'
        THEN (OrderTotal - ProposalWholesalePrice) +
             (ProposalWholesalePrice * 1.02)
        ELSE OrderTotal    
    END "New_OrderTotal"
FROM webservices.dbo.DT_Open_Orders_Baseprice
WHERE ProposalSerialNumber = '639036'

A:

SQL CASE expression has two forms:

The simple CASE expression, and
The searched CASE expression.

Simple CASE, i.e. CASE ProposalDate WHEN ... cannot be used with comparison operators; you need a searched CASE instead:
SELECT
    *
,   CASE
        WHEN ProposalDate > '2017-04-10 00:00:00.000'
        THEN (OrderTotal - ProposalWholesalePrice) + (ProposalWholesalePrice * 1.02)
        ELSE OrderTotal
    END "New_OrderTotal"
FROM webservices.dbo.DT_Open_Orders_Baseprice
WHERE ProposalSerialNumber = '639036'

