Get last updated value SQL - mysql

Question

I have the following table structure..
emp_id | base_rate | base_sal | effective_on
1001 26.22 1200 2015-10-12
1001 26.00 1100 2015-11-12
1001 26.00 1100 2015-12-12
1002 18 1200 2015-10-12
1002 19 1100 2015-11-12
I need to find get the last updated base_rate with effective_on date for each emp_id
Like output ..
1001 26.00 1100 2015-11-12
1002 19 1100 2015-11-12
See, for 1001 2015-11-12 is selected instead of 2015-12-12 which is latest as the base_rate is same and hence previously effective from 2015-11-12
I have tried.. everything.. not able to find the exact query..

Answer 1

This method is simple and easy to understand.
1) Assign rank for all the effective dates in descending order by partitioning
for each employee.
2) Select all the required fields for the last updated effective date from the
inner query and display the result.
SELECT emp_id,base_rate,base_sal
FROM
(
SELECT *,
ROW_NUMBER() OVER ( PARTITION BY emp_id ORDER BY effective_on DESC ) AS rn
FROM table
)
WHERE rn = 1;

Answer 2

One method is to generate a subset of employees with max effective on and join back to the base set..
In the below we generate set "B" with Emp_ID and ME (max effective) and then we join back to the entire data set in the table and use the columns emp_ID and ME to limit the data in the base set and return all columns we care about.
Put in English:
We generated a data set for all the employess with only their max effective date, and then joined this data set back to the base set to limit the data in the base set to only contain records for employees with their most recent effective_on date.
SELECT A.Emp_ID, A.Base_Rate, A.Base_Sal, min(C.Effective_On)
FROM Table A
INNER JOIN (SELECT emp_ID, Max(Effective_on) ME
FROM Table A
GROUP BY Emp_ID) B
on A.Emp_ID = B.Emp_ID
and A.Effective_ON = B.ME
INNER JOIN TABLE C
on C.Emp_ID = A.Emp_ID
and C.Base_Rate= A.Base_rate
and C.base_Sal = A.Base_Sal
GROUP BY A.Emp_ID, A.Base_Rate, A.Base_Sal
This is more or less database agnostic whereas a row_number and limit would not work on mySQL as it doesn't support window functions.

Answer 3

You can first get the minimum date each base_rate becomes effective on for every employee and then take the max from there. Here is how you can do it using row_number() in oracle:
with temp(emp_id, base_rate, base_sal, effective_on)
as (select 1001, 26.22, 1200, '2015-10-12' from dual union all
select 1001, 26.00, 1100, '2015-11-12' from dual union all
select 1001, 26.00, 1100, '2015-12-12' from dual union all
select 1002, 18, 1200, '2015-10-12' from dual union all
select 1002, 19, 1100, '2015-11-12' from dual
)
SELECT emp_id,base_rate,base_sal,effective_on FROM(
SELECT temp2.*,
row_number() OVER (PARTITION BY EMP_ID ORDER BY effective_on DESC) AS rn2
FROM
(
SELECT temp.*,
row_number() OVER (PARTITION BY EMP_ID, BASE_RATE ORDER BY effective_on) AS rn
FROM temp
) temp2
WHERE rn = 1
)
WHERE rn2 = 1;