SQL Query for fetching 2 results as single row - sql

Question

I have table like this. I want to get employee records to get their current Designation(whose effectiveto is null) and the date where they FIRST joined as Trainee(min(effectivefrom) where Designation= Trainee)
+----+-------------------+---------------+-------------+
| ID | Designation | EffectiveFrom | EffectiveTo |
+----+-------------------+---------------+-------------+
| 1 | Trainee | 01/01/2000 | 31/12/2000 |
| 1 | Assistant Manager | 01/01/2001 | 31/12/2004 |
| 1 | Suspended | 01/01/2005 | 01/02/2005 |
| 1 | Trainee | 02/03/2005 | 31/03/2005 |
| 1 | Manager | 01/04/2005 | NULL |
| 2 | Trainee | 01/01/2014 | 31/12/2014 |
| 2 | Developer | 01/01/2015 | 31/12/2016 |
| 2 | Architect | 01/01/2017 | NULL |
+----+-------------------+---------------+-------------+
How to get result like this
+----+---------------------+---------------------+
| ID | Current Designation | Date First Employed |
+----+---------------------+---------------------+
| 1 | Manager | 01/01/2000 |
| 2 | Architect | 01/01/2014 |
+----+---------------------+---------------------+

Answer 1

The date of first employment could be located using CROSS APPLY and SELECT TOP(1)
CREATE TABLE #table1(
ID int,
Designation varchar(17),
EffectiveFrom datetime,
EffectiveTo varchar(10));
INSERT INTO #table1
(ID, Designation, EffectiveFrom, EffectiveTo)
VALUES
(1, 'Trainee', '2000-01-01 01:00:00', '31/12/2000'),
(1, 'Assistant Manager', '2001-01-01 01:00:00', '31/12/2004'),
(1, 'Suspended', '2005-01-01 01:00:00', '01/02/2005'),
(1, 'Trainee', '2005-02-03 01:00:00', '31/03/2005'),
(1, 'Manager', '2005-01-04 01:00:00', NULL),
(2, 'Trainee', '2014-01-01 01:00:00', '31/12/2014'),
(2, 'Developer', '2015-01-01 01:00:00', '31/12/2016'),
(2, 'Architect', '2017-01-01 01:00:00', NULL);
select t.ID, t.Designation [Current Designation],
ef.EffectiveFrom [Date First Employed]
from #table1 t
cross apply (select top(1) cast(tt.EffectiveFrom as date) EffectiveFrom
from #table1 tt
where t.ID=tt.ID
and Designation='Trainee'
order by tt.EffectiveFrom) ef
where t.EffectiveTo is null;
ID Current Designation Date First Employed
1 Manager 2000-01-01
2 Architect 2014-01-01

Answer 2

One method is conditional aggregation. It is a bit unclear how you define "current", but assuming this is associated with EffectiveTo being NULL:
select id,
max(case when EffectiveTo is null then designation end) as current_designation,
min(effectivefrom) as start_ate
from t
group by id;

Answer 3

You can try below query:
select id,max(current_designation) current_designation,min(date_first_employee) date_first_employee from
(select id,
max(case when EffectiveTo is null then designation end) over (partition by id) as current_designation,
(case when Designation='Trainee' then EffectiveFrom end) Date_First_Employee
from desig) t
group by id
Output:

Answer 4

This is another possilbe solution
SQL Fiddle
MySQL 5.6 Schema Setup:
CREATE TABLE table1
(`ID` int, `Designation` varchar(17), `EffectiveFrom` datetime, `EffectiveTo` varchar(10))
;
INSERT INTO table1
(`ID`, `Designation`, `EffectiveFrom`, `EffectiveTo`)
VALUES
(1, 'Trainee', '2000-01-01 01:00:00', '31/12/2000'),
(1, 'Assistant Manager', '2001-01-01 01:00:00', '31/12/2004'),
(1, 'Suspended', '2005-01-01 01:00:00', '01/02/2005'),
(1, 'Trainee', '2005-02-03 01:00:00', '31/03/2005'),
(1, 'Manager', '2005-01-04 01:00:00', NULL),
(2, 'Trainee', '2014-01-01 01:00:00', '31/12/2014'),
(2, 'Developer', '2015-01-01 01:00:00', '31/12/2016'),
(2, 'Architect', '2017-01-01 01:00:00', NULL)
;
Query 1:
SELECT
ID,
(SELECT
`Designation`
FROM
table1
WHERE
`EffectiveFrom` = (SELECT
MAX(`EffectiveFrom`)
FROM
table1
WHERE
ID = t1.ID)) AS `Current Designation`
,DATE(MIN(`EffectiveFrom`)) AS `Date First Employed`
FROM
table1 t1
GROUP BY ID
Results:
| ID | Current Designation | Date First Employed |
|----|---------------------|---------------------|
| 1 | Trainee | 2000-01-01 |
| 2 | Architect | 2014-01-01 |

Answer 5

It's actually a rather simple self-join assuming that the EffectiveFrom and EffectiveTo columns are always filled in appropriately (i.e. there's always only one NULL value for EffectiveTo of a given ID). Since it's possible for someone to be a Trainee twice, you also need to use a window function like ROW_NUMBER() to filter out only the earliest Traininee EffectiveFrom date:
WITH CTE_Designations AS
(
SELECT T1.ID, T1.Designation AS CurrentDesignation, ISNULL(T2.EffectiveFrom, T1.EffectiveFrom) AS DateFirstEmployed -- If the join fails below then that means the earliest Designation is in T1 (e.g. that is the 'Trainee' record)
FROM DesignationsTable AS T1
LEFT JOIN DesignationsTable AS T2
ON T1.ID = T2.ID
AND T1.Designation <> T2.Designation
AND T2.Designation = 'Trainee'
WHERE T1.EffectiveTo IS NULL
),
CTE_Designations_FirstEmployedOnly AS
(
SELECT ID, CurrentDesignation, DateFirstEmployed, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY DateFirstEmployed) AS SortId -- Generates a unique ID per DateFirstEmployed row for each Designation.ID sorted by DateFirstEmployed
FROM CTE_Designations
)
SELECT ID, CurrentDesignation, DateFirstEmployed
FROM CTE_Designations_FirstEmployedOnly
WHERE SortId = 1
Results per your example data:
Results if you had an additional person who was still a Trainee:

Answer 6

This returns the result shown for the given data
Solves for "current Designation(whose effectiveto is null) and the date where they FIRST joined". Also handles terminated employees where EffectiveTo is not NULL as well as new employees with a single row. Replace "#t" with your table name.
SELECT a.Id, d.Designation, a.EffectiveFrom
FROM
(SELECT *, ROW_NUMBER() OVER ( PARTITION BY Id ORDER BY EffectiveFrom ASC ) r FROM #t) a
INNER JOIN
(SELECT *, ROW_NUMBER() OVER ( PARTITION BY Id ORDER BY EffectiveFrom DESC ) r FROM #t) d
ON a.Id = d.Id
WHERE a.r = 1 AND d.r = 1
Result:
Id Designation EffectiveFrom
1 Manager 2000-01-01
2 Architect 2014-01-01