How to compare different values within the same column - sql

Question

I having two tables emp and type.
create table EMP(ID number(10), effective_date date);
EID Effective_date
--------------------
1 02/14/2023
2 02/15/2023
3 04/30/2023
4 03/24/2023
create table type(ID number(10),contract_type varchar2(2));
TID contract_type
------------------
1 P
1 S
1 P
2 S
2 S
3 P
3 S
4 S
I am looking EID which is having contract type is 'S' in type table. (or emp table with effective date is greater than sysdate and in the type table with only contract_type ='S')
Actual result :
2
4
My query is not giving the correct results.
select emp.EID
from emp,type
where EID = TID
contract_type ='S'
effective_date >= sysdate
group by TID
having count(TID) >= 1;

Answer 1

If you want to keep your idea with COUNT and GROUP BY, you should count other contract types than the 'S' ones and check this is 0:
SELECT e.eid
FROM emp e
JOIN type t ON e.eid = t.tid
WHERE
e.effective_date >= sysdate
GROUP BY e.eid
HAVING COUNT(CASE WHEN t.contract_type <> 'S' THEN 1 END) = 0;
This query will return 2 and 4 for your sample data.
Try out: db<>fiddle
Another option is as already said here using NOT EXISTS.
Take care of following difference to the NOT EXISTS approach: The query in Tim's answer will also fetch id's of table "emp" that don't appear at all in table "type". My query here will not fetch such id's.
It's up to you to decide whether this is possible at all and what to do in this case.
Changing JOIN to LEFT JOIN in above query will eliminate this difference.

Answer 2

I would use exists logic here:
SELECT EID
FROM EMP e
WHERE effective_date >= SYSDATE AND
NOT EXISTS (
SELECT 1
FROM "type" t
WHERE t.TID = e.EID AND
t.contract_type <> 'S'
);

Answer 3

You could use Count() Over() analytic function to check for type 'S' and number of different types per ID.
SELECT DISTINCT ID
FROM ( Select e.EID "ID",
Count(CASE t.CONTRACT_TYPE WHEN 'S' THEN 'S' END) Over(Partition By t.ID Order By t.ID) "NUM_OF_S",
Count(Distinct t.CONTRACT_TYPE) Over(Partition By t.ID) "NUM_OF_TYPES",
TRUNC(e.EFFECTIVE_DATE) - TRUNC(SYSDATE) "DAYS_AFTER_SYSDATE"
From emp_cte e
Inner Join type_cte t ON(t.ID = e.EID) )
WHERE NUM_OF_S > 0 And -- Type 'S' exists for ID AND
NUM_OF_TYPES = 1 And -- It is the only type AND
DAYS_AFTER_SYSDATE > 0 -- EFFECTIVE_DATE is after SYSDATE
With your sample data ...
WITH
emp_cte(EID, EFFECTIVE_DATE) AS
(
Select 1, To_Date('02/14/2023', 'mm/dd/yyyy') From Dual Union All
Select 2, To_Date('02/15/2023', 'mm/dd/yyyy') From Dual Union All
Select 3, To_Date('04/30/2023', 'mm/dd/yyyy') From Dual Union All
Select 4, To_Date('03/24/2023', 'mm/dd/yyyy') From Dual
),
type_cte(ID, CONTRACT_TYPE) AS
(
Select 1, 'P' From Dual Union All
Select 1, 'S' From Dual Union All
Select 1, 'P' From Dual Union All
Select 2, 'S' From Dual Union All
Select 2, 'S' From Dual Union All
Select 3, 'P' From Dual Union All
Select 3, 'S' From Dual Union All
Select 4, 'S' From Dual
)
... result would be ...
-- ID
-- ----------
-- 2
-- 4