FR: Allow simple CASE statements

[thefreakquency]

There are two types of SQL CASE statements:

-- Simple CASE expression:
CASE input_expression
     WHEN when_expression THEN result_expression [ ...n ]
     [ ELSE else_result_expression ]
END

-- Searched CASE expression:
CASE
     WHEN Boolean_expression THEN result_expression [ ...n ]
     [ ELSE else_result_expression ]
END

Currently, SWQL only supports the latter.

The simple CASE expression is much more efficient as the server does not need to redo the query every time. Imagine the following:

CASE
    WHEN (SELECT TOP 1 cpa.CurrentValue 
        FROM Orion.NPM.CustomPollerAssignment cpa
        Inner JOIN Orion.Nodes n2
        ON cpa.NodeID = n2.NodeID
        WHERE cpa.CustomPollerName = 'dm2EngineStatus' AND N2.NodeID = n.NodeID ) > 1  THEN 'Down.gif'
    WHEN (SELECT TOP 1 cpa.CurrentValue         
        FROM Orion.NPM.CustomPollerAssignment cpa
        Inner JOIN Orion.Nodes n2
        ON cpa.NodeID = n2.NodeID
        WHERE cpa.CustomPollerName = 'dm2EngineStatus' AND N2.NodeID = n.NodeID ) = 1 THEN 'Warning.gif'
    WHEN (SELECT TOP 1 cpa.CurrentValue 
        FROM Orion.NPM.CustomPollerAssignment cpa
        Inner JOIN Orion.Nodes n2
        ON cpa.NodeID = n2.NodeID
        where cpa.CustomPollerName = 'dm2EngineStatus' AND N2.NodeID = n.NodeID ) = 0 THEN 'up.gif'
    ELSE 'Unknown.gif'
    END AS EngineStatusLED,

could simply be changed by putting the search query as input:

 CASE (SELECT TOP 1 cpa.CurrentValue 
        FROM Orion.NPM.CustomPollerAssignment cpa
        Inner JOIN Orion.Nodes n2
        ON cpa.NodeID = n2.NodeID
        WHERE cpa.CustomPollerName = 'dm2EngineStatus' AND N2.NodeID = n.NodeID )
    WHEN > 1  THEN 'Down.gif'
    WHEN = 1 THEN 'Warning.gif'
    WHEN = 0 THEN 'up.gif'
    ELSE 'Unknown.gif'
    END AS EngineStatusLED,

This is especially bugging me as we also cant use a sub-select value (i.e. SELECT X FROM Y as Z) from the same main query as an input. I have a use case where for a single value, I have 62 CASE possibilities to match (and that's only for a single column)...