How to insert data into temp table using Case statement in SQL - sql

Question

I am trying to insert the data into temp table using Case statement below is my code, and with this I am getting this error
Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.
I'm not able to figure out what I am doing wrong. Is this the correct way of inserting the data into a temp table based on certain condition provided in Case statement?
DECLARE #temp_idCol TABLE
(
uid int IDENTITY(1, 1),
id nvarchar(20)
)
DECLARE #_ThresholdOperator nvarchar(20) = '=',
#_Threshold_Val nvarchar(20) = '0.4'
INSERT INTO #temp_idCol (id)
SELECT
CASE
WHEN #_ThresholdOperator = '='
THEN (SELECT q.id
FROM [dbo].[Summit_Twitter_HashtagDetails] q
WHERE q.Ticket_ID IS NULL
AND q.SentimentAnalyis_Score = #_Threshold_Val
OR q.IsProcessedOrNot = 0)
WHEN #_ThresholdOperator = '>'
THEN (SELECT q.id
FROM [dbo].[Summit_Twitter_HashtagDetails] q
WHERE q.Ticket_ID IS NULL
AND q.SentimentAnalyis_Score > #_Threshold_Val
OR q.IsProcessedOrNot = 0)
WHEN #_ThresholdOperator = '<'
THEN (SELECT q.id
FROM [dbo].[Summit_Twitter_HashtagDetails] q
WHERE q.Ticket_ID IS NULL
AND q.SentimentAnalyis_Score < #_Threshold_Val
OR q.IsProcessedOrNot = 0)
END AS id
FROM
[dbo].[Summit_Twitter_HashtagDetails]

Answer 1

A CASE expression can only return 1 value.
But you can use IF and ELSE
Simplified example:
create table test (id int identity primary key, col decimal(9,1));
insert into test (col) values (0.1),(0.2),(0.3),(0.4),(0.5);
declare #ids table (id int);
declare #_ThresholdOperator varchar(2) = '>',
#_Threshold_Val nvarchar(20) = '0.3';
IF #_ThresholdOperator = '='
insert into #ids (id)
select id from test where col = #_Threshold_Val;
ELSE IF #_ThresholdOperator = '<'
insert into #ids (id)
select id from test where col < #_Threshold_Val;
ELSE IF #_ThresholdOperator = '>'
insert into #ids (id)
select id from test where col > #_Threshold_Val;
ELSE BEGIN
insert into #ids (id) values (0);
update #ids set id = id + 42;
END;
select * from #ids;
id
4
5
db<>fiddle here
Extra
A CASE could still be used in the WHERE clause.
As long it only returns 1 value.
It's just not sargable.
insert into #ids (id)
select id from test
where case #_ThresholdOperator
when '=' then iif(col=#_Threshold_Val,1,0)
when '<' then iif(col<#_Threshold_Val,1,0)
when '>' then iif(col>#_Threshold_Val,1,0)
end = 1;