Making a case statement when a count condition is bigger than 0 - sql

Question

I want to make a pretty complex SQL query, which results in 0/1 or TRUE/FALSE depending on my conditions.
Idea is that I have a customer table, and then I want to make a couple of checks in different tables, and then if either is true, then we return TRUE, and if not, FALSE:
I was thinking to do this with CASE. See example below:
select
case
((select count(*) from boughtleads bl where bl.customerid = cu.id)>0)
then 'TRUE'
else 'FALSE'
end
from customers cu
left join leadagents la on la.customerid = cu.id
where cu.vatnumber = '30218124'
This returns:
Msg 102, Level 15, State 1, Line 3
Incorrect syntax near '>'.
My challenge is then. First of all, the above query fails for some reason, my other problem is I can't use an OR.
My ideal pseudocode would be something like:
select
case
(
((select count(*) from boughtleads bl where bl.customerid = cu.id)>0)
OR
((select count(*) from leadnotifications ln where ln.leadagentid = la.id)>))
then 'TRUE'
else 'FALSE'
end
from customers cu
left join leadagents la on la.customerid = cu.id
where cu.vatnumber = '30218124'
Any ideas on how to attack this?

Answer 1

You are missing when:
select (case when (select count(*) from boughtleads bl where bl.customerid = cu.id) > 0
then 'TRUE'
else 'FALSE'
end)
from customers cu left join
leadagents la
on la.customerid = cu.id
where cu.vatnumber = '30218124';
That said, from a performance perspective it is better to write such conditions using exists:
select (case when exists (select 1 from boughtleads bl where bl.customerid = cu.id)
then 'TRUE'
else 'FALSE'
end)
from customers cu left join
leadagents la
on la.customerid = cu.id
where cu.vatnumber = '30218124'
The count(*) version has to find all matching rows in boughtleads. The exists version can stop at the first match.