CASE WHEN用法

select  
    CASE 'R'
        WHEN 'Y' THEN '等于Y'
        WHEN 'N' THEN '等于N'
        ELSE '不等于Y与N'
    END

select 
    CASE 
        WHEN name > 'A' THEN 'A'
        WHEN name < 'B' THEN 'B'
        WHEN name = 'C' THEN 'C' 
        ELSE '.....' 
    END