Creating conditional column in SQL - tsql

Question

I am trying to create a conditional column in T-SQL like an if statement but rather than printing a string I would like it to pull through data from another column in the data set.
SELECT
CASE
WHEN NameDay = 'Sunday'
THEN [sales]
ELSE [SunAdj]
END AS AdjustedDays
FROM
Table
Basically I want it to pull data from the [sales] column if the day in the NameDay column is 'Sunday' otherwise pull it from [SunAdj]. I can get it to work populating a string but not data from other columns. Is this possible? If so how? Any help would be much appreciated.
Product category Sales SunAdj NameDay
--------------------------------------------------
Meat 1000 3500 Sunday
Fish 1000 3500 Wednesday
Bakery 1000 3500 Friday
I would want another column called AdjustedDays showing 1000 for the first row and 3500 for the others.

Answer 1

This is a quick CTE setup of the data in the question:
; with sourceData (Product, Category, Sales, SunAdj, NameDay)
as
(
select 'Meat', null, 1000, 3500, 'Sunday'
union select 'Fish', null, 1000, 3500, 'Wednesday'
union select 'Bakery', null, 1000, 3500, 'Friday'
)
...
and we can use it to show that your statement is already correct:
; with sourceData (Product, Category, Sales, SunAdj, NameDay)
as
(
select 'Meat', null, 1000, 3500, 'Sunday'
union select 'Fish', null, 1000, 3500, 'Wednesday'
union select 'Bakery', null, 1000, 3500, 'Friday'
)
select
Product, Category, Sales, SunAdj, NameDay,
CASE when NameDay = 'Sunday' then [sales]
else [SunAdj] end as AdjustedDays
from sourceData
Just to add a little value to my answer, you can achieve the same thing with the IIF function:
; with sourceData (Product, Category, Sales, SunAdj, NameDay)
as
(
select 'Meat', null, 1000, 3500, 'Sunday'
union select 'Fish', null, 1000, 3500, 'Wednesday'
union select 'Bakery', null, 1000, 3500, 'Friday'
)
select
Product, Category, Sales, SunAdj, NameDay, iif(NameDay='Sunday', SunAdj, Sales) AdjustedDays
from sourceData
Both queries give the same result:
Product Category Sales SunAdj NameDay AdjustedDays
------- ----------- ----------- ----------- --------- ------------
Bakery NULL 1000 3500 Friday 1000
Fish NULL 1000 3500 Wednesday 1000
Meat NULL 1000 3500 Sunday 3500