Use Count function inside conditional part of Case Expression - sql

Question

I have two tables with the following sample records in oracle database
1. staffs
inst_name name sid
ABC John 1
PQR Sam 2
ABC Tom 3
ABC Amit 4
PQR Jack 5
2. staffaccounts
sid account_no
1 4587
1 4588
2 4589
3 4581
3 4582
5 4583
5 4585
4 4586
Where I want the result like
inst_name account_type total
PQR SINGLE 1
ABC SINGLE 1
PQR DOUBLE 1
ABC DOUBLE 2
This can be achieved by a outer query, but I want to write a query where there is no outer query. Want to accomplish it in one single query.
SELECT
A .inst_name,
(
CASE COUNT (b.ac_no)
WHEN 1 THEN
'Single'
WHEN 2 THEN
'Double'
END
) account_type,
COUNT (A . NAME)
FROM
staffs A,
staffaccounts b
WHERE
A . s_id = b.s_id
GROUP BY
A .inst_name
The above query gives error ORA-00907: missing right parenthesis. Can it be done in single query or is outer query the only way out.
Oracle Version is 10g

Answer 1

May be something like this would work.
SELECT
A.inst_name,
CASE COUNT (b.account_no)
WHEN 1 THEN
'Single'
WHEN 2 THEN
'Double'
END account_type,
COUNT (A.name)
FROM
staffs A JOIN
staffaccounts b
ON
A.SID = b.sid
GROUP BY
A.inst_name , a.sid
ORDER BY 3;

Answer 2

You are grouping by inst_name, but this is not what you actually want, because you don't want a result row per inst_name, but per inst_name and account_type.
select
s.inst_name,
sa.account_type,
count(*) as total
from staffs s
join
(
select
sid,
case when count(*) = 1 then 'SINGLE' else 'DOUBLE' end as account_type
from staffaccounts
group by sid
having count(*) <= 2
) sa on sa.sid = s.sid
group by sa.account_type, s.inst_name
order by sa.account_type, s.inst_name;

Answer 3

You should learn how to properly use JOIN syntax. I prefer the explicit comparison syntax for CASE.
This may be what you want:
SELECT s.inst_name,
(CASE WHEN COUNT(sa.ac_no) = 1 THEN 'Single'
WHEN COUNT(sa.ac_no) = 2 THEN 'Double'
END) as account_type,
COUNT(*)
FROM staffs s JOIN
staffaccounts sa
ON s.SID = sa.sid
GROUP BY s.inst_name;
EDIT:
Now I see what you want:
SELECT s.inst_name,
(CASE WHEN cnt = 1 THEN 'Single'
WHEN cnt = 2 THEN 'Double'
END) as account_type,
COUNT(*)
FROM (SELECT s.*, COUNT(*) as cnt
FROM staffs s JOIN
staffaccounts sa
ON s.SID = sa.sid
GROUP BY s.id
) s
GROUP BY s.inst_name,
(CASE WHEN cnt = 1 THEN 'Single'
WHEN cnt = 2 THEN 'Double'
END);

Answer 4

I got only the way by using subquery but is in the easy way (more easier and readable) to achieve your requirement
SELECT inst_name, account_type, count(total) as total
FROM (
SELECT
a.inst_name,
CASE
WHEN COUNT (b.account_no) = 1 THEN 'Single'
WHEN COUNT (b.account_no) = 2 THEN 'Double'
END AS account_type,
COUNT (a.name) AS total
FROM staffs a
INNER JOIN staffaccounts b ON A . SID = b.sid
GROUP BY a.inst_name, a.sid) t GROUP BY inst_name, account_type
OUTPUT:
inst_name account_type total
ABC Double 2
PQR Double 1
ABC Single 1
PQR Single 1