How do I use "date" function with case statement in snowflake - snowflake-cloud-data-platform

Question

I have this case statement attached to a code. But it's not working as it should. It is bringing "false" in the (Treaty Column) instead of the respected Treaties assigned. My thought is, it's not recognizing the dates as "Date". Can anyone tell me what I am doing wrong or how to apply the "Date" function to the case statement? Thank you!
set Reference_Org_Var = 'HII_STM';
set Load_Date_Var = current_date();
set Treaty_Var = ' ';
insert into PREMIUM_DB(Plan_Name, Member_ID,
"3x2_Term", Member_Policy_Effective_Date,
Reference_Org, Treaty, LoadDt)
select Plan_Name, Member_ID, '3x2_Term',
Member_Policy_Effective_Date,
FileRecdDate, $Reference_Org_Var,
case
when Member_Policy_Effective_Date <= '2017-02-28'
then $Treaty_Var = '2016 Treaty'
when Member_Policy_Effective_Date between '2017-03-01' and '2018-02-28'
then $Treaty_Var = '2017 Treaty'
when Member_Policy_Effective_Date between '2018-03-01' and '2018-09-30'
then $Treaty_Var = '2018a Treaty'
when Member_Policy_Effective_Date between '2018-10-01' and '2018-10-31'
then $Treaty_Var = '2018b Treaty'
else $Treaty_Var = ' '
end,
$Load_Date_Var
from HII_STM_PREM;

Answer 1

You are setting the value of your Treaty column to the result of an equality check, but you seem to actually just want the value on the right hand side which you can achieve by changing your query to use THEN statements to THEN '2017 Treaty' etc (instead of THEN $Treaty_Var = '2017 Treaty')
set Treaty_Var = ' ';
WITH HII_STM_PREM as (select $1 Member_Policy_Effective_Date from VALUES ('2017-02-20'),
('2018-02-28'),
('2017-03-01'),
('2018-03-01'),
('2018-09-30'),
('2018-10-01'),
('2018-10-31'))
select
case
when Member_Policy_Effective_Date <= '2017-02-28'
then $Treaty_Var = '2016 Treaty'
when Member_Policy_Effective_Date between '2017-03-01' and '2018-02-28'
then $Treaty_Var = '2017 Treaty'
when Member_Policy_Effective_Date between '2018-03-01' and '2018-09-30'
then $Treaty_Var = '2018a Treaty'
when Member_Policy_Effective_Date between '2018-10-01' and '2018-10-31'
then $Treaty_Var = '2018b Treaty'
else $Treaty_Var = ' '
end current_val,
case
when Member_Policy_Effective_Date <= '2017-02-28'
then '2016 Treaty'
when Member_Policy_Effective_Date between '2017-03-01' and '2018-02-28'
then '2017 Treaty'
when Member_Policy_Effective_Date between '2018-03-01' and '2018-09-30'
then '2018a Treaty'
when Member_Policy_Effective_Date between '2018-10-01' and '2018-10-31'
then '2018b Treaty'
else ' '
end expected_val
from HII_STM_PREM;
CURRENT_VAL EXPECTED_VAL
FALSE 2016 Treaty
FALSE 2017 Treaty
FALSE 2017 Treaty
FALSE 2018a Treaty
FALSE 2018a Treaty
FALSE 2018b Treaty
FALSE 2018b Treaty