case when语句后的表达式

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

CASE od.ObjectType
    WHEN 1 THEN(SELECT TOP 1 StructureName FROM TBL_StationStructure WHERE StructureType=2)
    WHEN 2 THEN (SELECT TOP 1 StructureName FROM TBL_StationStructure WHERE StructureId=od.ObjectId)
END