Sub-query producing multiple rows error - Need multiple rows to be selected - SQL

Question

I have a scenario. Below are my 3 tables:

create table #cdes(client_id int,identifier int)

insert #cdes values(9908,789654123)

---

create table #temp1
(
     client_id int, 
     identifier int, 
     pp_id int,
     ch_id int,
     code varchar(20),
     program varchar(20),
     startdate date,
     enddate date, 
     ssc varchar(50)
)

insert into #temp1
values (9908,789654123,1567,1566,'OP','xASMT','1/1/2019','1/4/2019','A201901044F010134NNN01D               151 143 093 ')
-------------------------------------------
create table #temp2
(
     client_id int, 
     identifier int, 
     pp_id int,
     ch_id int,
     code varchar(20), 
     program varchar(20),
     startdate date,
     enddate date, 
     ssc varchar(20)
)

insert into #temp2
values(9908,789654123,1574,1573,'OP','SU1','1/1/2019','1/4/2019',NULL)

I have a case condition in my final select query as my query revolves around multiple conditions.Most case conditions throw only one row as output however, I want to report multiple lines for a specific scenario.

My desired output:

My query:

select 
d.client_id,
case when d.client_id = 9908
then
(
select CONCAT(t1.code,t1.startdate,t1.enddate,t1.ssc)
from #temp1 t1
left join #temp2 t2 on t1.client_id = t2.client_id and t1.identifier = t2.identifier
union all
select CONCAT(t2.code,t2.startdate,t2.enddate,t2.ssc)
from #temp1 t1
left join #temp2 t2 on t1.client_id = t2.client_id and t1.identifier = t2.identifier)
end

from #cdes d
left join #temp1 t1 on d.client_id = t1.client_id
left join #temp2 t2 on d.client_id = t2.client_id 

The problem is Unionall is producing myltiple rows that I am finding difficult to accommodate in my select statement. Any help?!

This case condition is fake. I have included for just a sample.

Answer 1

Don't put a UNION ALL query in your subquery. make your entire query a UNION ALL query.

Instead of:

SELECT ColA, ColB, (
  SELECT CalculationX FROM MyTable 
  UNION ALL 
  SELECT CalculationY FROM MyTable
) AS ColC
FROM MyTable

You need something like this:

SELECT ColA, ColB, CalculationX AS ColC FROM MyTable
UNION ALL
SELECT ColA, ColB, CalculationY AS ColC FROM MyTable

Answer 2

You already have the subquery so just add the condition after where :

select t.* from (
select t1.client_id client_id, t1.identifier identifier, CONCAT(t1.code,t1.startdate,t1.enddate,t1.ssc) ssc_concatenated
from #temp1 t1
union all
select t2.client_id client_id, t2.identifier identifier, CONCAT(t2.code,t2.startdate,t2.enddate,t2.ssc) ssc_concatenated
from #temp2 t2) t
where t.client_id in (select client_id from #cdes)

or

where t.client_id = 9908

Or you can add the condition directly in each part of the subquery:

select t.* from (
select t1.client_id client_id, t1.identifier identifier, CONCAT(t1.code,t1.startdate,t1.enddate,t1.ssc) ssc_concatenated
from #temp1 t1
where t1.client_id = 9908
union all
select t2.client_id client_id, t2.identifier identifier, CONCAT(t2.code,t2.startdate,t2.enddate,t2.ssc) ssc_concatenated
from #temp2 t2
where t2.client_id = 9908