SQL：如何用两个替换一个？

Question

我有一个表 “第一”：

我想编写一个查询。

If first.type = 'MM' 

    then replace this line in two new lines 

    where first.type = 'HH' and first.type = 'VV'. 

例如：线，其中first.type = 'MM'：

我要替换这一行这样的：

而结果：

有人对此有何看法？

我正在使用MS SQL Server Management Studio Express。

Answer 1

 

select id,freq,parity,line,type,gain,obdim from [first] where type<>'MM' 
union 
select id,freq,parity,line,'HH' as type,gain,obdim from [first] where type='MM' 
union 
select id,freq,parity,line,'VV' as type,gain,obdim from [first] where type='MM' 
 

Answer 2

select id,frequency, 'VV' type --, .. 
from table1 
where type='MM' 
union all 
select id,frequency, 'HH' as type --, .. 
from table1 
where type='MM' 

Answer 3

这种解决方案可能是在这个意义上非常特殊，它意味着type列只能有值HH，MM，或VV。

SELECT 
    f.ID, 
    f.freq, 
    f.parity, 
    f.line, 
    t.type, 
    f.gain, 
    f.obdim 
FROM [first] f 
    INNER JOIN (
    SELECT 'HH' AS type 
    UNION ALL 
    SELECT 'VV' 
) t ON f.type IN (t.type, 'MM')