Getiing multiple rows as output using case statement in sql - sql

Question

I have a table,
id category column1 column2 column3
1 1 val1a val1b val1c
2 2 val2a val2b val2c
3 3 val3a val3b val3c
from which I need to select columns based on multiple conditions something like below.
SELECT id, category, column1, column2, column3
FROM table
WHERE id = #id
AND category IN (
select case when (#input1='Yes' AND #input2='Yes') then (select category from table where category in ('1','2'))
when (#input1='Yes' AND #input2='No') then (select category from table where category ='1')
when (#input1='No' AND #input2='Yes') then (select category from table where category ='2')
else ''
end as category)
END
Input values #input1 and #input2 are grabbed from another table, need to select and output rows with category in ('1','2') according to above condition.
What I need -
if input1=Yes and input2=Yes output rows with category in ('1','2')
if input1=Yes and input2=No output rows with category in ('1')
if input1=No and input2=Yes output rows with category in ('2')
if input1=No and input2=No output rows with category in ('')
Does case statement output multiple values? Need help.

Answer 1

check out the code below, you don't need to use CASE WHEN, just use where condition combinations will do the trick.
create table [Test] ( id int, category nvarchar(10));
insert [Test] values(1,'1');
insert [Test] values(2,'2');
insert [Test] values(3,'1');
insert [Test] values(4,'2');
declare #input1 varchar(10) = 'Yes'
declare #input2 varchar(10) = 'No'
SELECT id, category
FROM [Test]
WHERE
(
( #input1 = 'Yes' and category ='1')
or
( #input2 = 'Yes' and category ='2')
)

Answer 2

If you wanted to use in, you could use:
where id = #id and
category in ( (case when #input1 = 'Yes' then 1 end),
(case when #input2 = 'Yes' then 2 end)
)
The default value for the case is NULL and that will fail any comparison.
Also, note that I removed the single quotes around '1' and '2'. These look like numbers, so I assume that category is a number. Quotes should only be used around string and date constants.

Answer 3

Maybe this:
SELECT id, category, column1, column2, column3
FROM table
WHERE id = #id
AND category IN
(
select category
from table
where
(
category = '1'
AND
#input1='Yes'
)
OR
(
category = '2'
AND
#input1='Yes'
)
)
or this:
SELECT id, category, column1, column2, column3
FROM table
WHERE id = #id
AND
(
(
#input1='Yes' AND #input2='Yes' AND category IN (select category from table where category in ('1','2')
)
OR
(
#input1='Yes' AND #input2='No' AND category IN (select category from table where category ='1')
)
OR
(
#input1='No' AND #input2='Yes' AND category IN (select category from table where category ='2')
)
)

Answer 4

I would suggest you to form a mapping table and leverage it in the SELECT query. It will result in simplified code and more clear approach.
;WITH CTE_MappingTable AS
(
SELECT *
FROM
(
values
('Yes','Yes',1),
('Yes','Yes',2),
('Yes','No',1),
('No','Yes',2)
) as t(input1,input2,category)
)
SELECT id, category, column1, column2, column3
FROM table as t
INNER JOIN CTE_MappingTable as c
ON c.Category = t.Category
WHERE id = #id AND c.input1 = #input1 AND c.input2 = #input2