case

The case expression goes through conditions and returns a value when the first condition is met (like an if-else statement).

The case expression must contain at least one when...then... expression. Once a when condition is true, it will stop reading and return the result specified in the then clause. If no conditions are true, it returns the value in the else clause. If there is no else part and no conditions are true, it returns NULL. The return type of all conditions in a case expression must be the same.

The case...when... expression can be used in distributed queries.

Syntax

case
    when condition_1 then expression_1
    [when condition_2 then expression_2]
    ...
    [when condition_n then expression_n]
    [else expression_end]
end

Starting from version 2.00.10, the when and then clauses of a CASE expression no longer need to be written on a single line.

Examples

t = table(`st0`st1`st2`st4`st5`st6 as sym, 80 200 150 220 130 190 as vol)
select sym, case 
	when vol < 100 then -1 
	when vol < 200 then 0
	else 1
end as flag
from t


sym	flag
st0	-1
st1	1
st2	0
st4	1
st5	0
st6	0

t = table(2022.01.01 2022.01.01 2022.01.01 2022.01.01 2022.01.01 2022.01.01 as date, `a`a`b`b`a`b as id, 300 290 302 296 304 320 as val)
select date, case when t.id == `a then val end as `GroupA, case when t.id == `b then val end as `GroupB from t


date	GroupA	GroupB
2022.01.01	300
2022.01.01	290
2022.01.01		302
2022.01.01		296
2022.01.01	304
2022.01.01		320

select sum(val) as total from t group by case when t.val < 300 then 0 else 1 end as flag


flag	total
1	1,226
0	586

Use analytic functions in a case expression.

t = table([2023.06M,2023.07M,2023.08M,2023.07M,2023.07M,2023.06M,2023.08M,2023.06M,2023.08M] as month, ["A","A","B","B","C","C","A","B","C"] as flag, [1200,1500,1200,1300,1400,1400,1400,1000,1300] as val)
t


month	flag	val
2023.06M	A	1,200
2023.07M	A	1,500
2023.08M	B	1,200
2023.07M	B	1,300
2023.07M	C	1,400
2023.06M	C	1,400
2023.08M	A	1,400
2023.06M	B	1,000
2023.08M	C	1,300

For flag "A", calculate the value deviation from monthly average. For other flags, calculate the standard deviation of value for the month.

select month,flag,(case when flag = "A"
then (val - avg(val)over(partition by month))
else std(val)over(partition by month) end) as value
from t


month	flag	value
2023.06M	A	0
2023.07M	A	100
2023.08M	B	100
2023.07M	B	100
2023.07M	C	100
2023.06M	C	200
2023.08M	A	100
2023.06M	B	200
2023.08M	C	100