MSSQL-只能选择一行中具有不同值的列

Question

Imagine, I have an audit table that contains the following columns:

id   schedule   weekday   weekday_old   weekend   weekend_old
1    week1      m,t,w     th,f          sa,su     sa,su
1    week2      m,t,w     m,t,w         sa,su     sa,su
1    week3      m,t,w     w,th,f        sa,su     sa
1    week4      m,t,w     m,t,w         sa,su     sa,su
1    week5      m,t,w     m,t,w         sa,su     sa,su
1    week6      m,t,w     m,t,w         sa        su    
1    week7      m,t,w     m,t,w         sa        su  

Is there a sql command(s) that will allow me to select only the rows where data in the weekday/weekday_old is different, or weekend/weekend_old is different, or (when weekday/weekday_old and weekend/weekend_old) is different and replace the values in columns that are same with null?

So, using the above table, I would like the following to be returned

week1      m,t,w     th,f          null     null
week3      m,t,w     w,th,f        sa,su    sa
week6      null      null          sa        su    
week7      null      null          sa        su  

This probably sounds crazy, but we try to do what we're asked with the tools we have. Looking forward to any help. Thank you.

**I removed week4 from results table. It was typo.

Answer 1

What you described doesn't match your sample (why would week4 selected and is not null). Assuming it was a typo:

SELECT schedule, 
NULLIF(weekday,weekday_old) AS weekday,
NULLIF(weekday_old,weekday) AS weekday_old,
NULLIF(weekend,weekend_old) AS weekend,
NULLIF(weekend_old,weekend) AS weekend_old
 FROM dbo.mytable 
 WHERE NULLIF(weekday,weekday_old) IS NOT NULL or NULLIF(weekend,weekend_old) IS NOT NULL;

Answer 2

您可能可以使用CASE表达式，例如

CASE WHEN weekday =  weekday_old THEN NULL ELSE weekday END AS weekday