我是否需要为每个字段重写case语句？

Question

两列的大小写条件是相同的。在下面的语句中，我两次使用了此条件，但对于不同的列，是否还有其他方法不重复两次条件？

case [CPHIL_AWD_CD]
                     when ' ' then 'Not Applicable/ Not a Doctoral Student'
                     when 'X' then 'Not Applicable/ Not a Doctoral Student'
                     when 'N' then 'NO'
                     when 'Y' then 'YES'
                end as CPHIL_AWD_CD

              ,case [FINL_ORAL_REQ_CD] 
                     when ' ' then 'Not Applicable/ Not a Doctoral Student'
                     when 'X' then 'Not Applicable/ Not a Doctoral Student'
                     when 'N' then 'NO'
                     when 'Y' then 'YES'
                end as FINL_ORAL_REQ_CD

Answer 1

thepirat000答案的变体：

-- Sample data.
declare @Samples as Table (
  Frisbee Int Identity Primary Key, Code1 Char(1), Code2 Char(2) );
insert into @Samples values ( 'Y', 'N' ), ( ' ', 'Y' ), ( 'N', 'X' );
select * from @Samples;

-- Handle the lookup.
with Lookup as (
  select * from ( values
    ( ' ', 'Not Applicable/ Not a Doctoral Student' ),
    ( 'X', 'Not Applicable/ Not a Doctoral Student' ),
    ( 'N', 'No' ),
    ( 'Y', 'Yes' ) ) as TableName( Code, Description ) )
select S.Code1, L1.Description, S.Code2, L2.Description
    from @Samples as S inner join
      Lookup as L1 on L1.Code = S.Code1 inner join
      Lookup as L2 on L2.Code = S.Code2;

查找表是在CTE中创建的，并根据需要为多列进行引用。

更新： 由于某些莫名其妙的原因，表变量现在被赋予了主键。如果有人可以真正解释一下它将如何提高性能，那么我很想听听它。从执行计划来看并不明显。