LAG of MIN in SQL Analytic - sql-server

Question

I have a table containing employees id, year id, client id, and the number of sales. For example:
--------------------------------------
id_emp | id_year | sales | client id
--------------------------------------
4 | 1 | 14 | 1
4 | 1 | 10 | 2
4 | 2 | 11 | 1
4 | 2 | 17 | 2
For a employee, I want to obtain rows with the minimum sales per year and the minimum sales of the previous year.
One of the queries I tried is the following:
select distinct
id_emp,
id_year,
MIN(sales) OVER(partition by id_emp, id_year) AS min_sales,
LAG(min(sales), 1) OVER(PARTITION BY id_emp, id_year
ORDER BY id_emp, id_year) AS previous
from facts
where id_emp = 4
group by id_emp, id_year, sales;
I get the result:
-------------------------------------
id_emp | id_year | sales | previous
-------------------------------------
4 | 1 | 10 | (null)
4 | 1 | 10 | 10
4 | 2 | 11 | (null)
but I expect to get:
-------------------------------------
id_emp | id_year | sales | previous
-------------------------------------
4 | 1 | 10 | (null)
4 | 2 | 11 | 10

Answer 1

SQL Fiddle
Oracle 11g R2 Schema Setup:
CREATE TABLE EMPLOYEE_SALES ( id_emp, id_year, sales, client_id ) AS
SELECT 4, 1, 14, 1 FROM DUAL
UNION ALL SELECT 4, 1, 10, 2 FROM DUAL
UNION ALL SELECT 4, 2, 11, 1 FROM DUAL
UNION ALL SELECT 4, 2, 17, 2 FROM DUAL;
Query 1:
SELECT ID_EMP,
ID_YEAR,
SALES AS SALES,
LAG( SALES ) OVER ( PARTITION BY ID_EMP ORDER BY ID_YEAR ) AS PREVIOUS
FROM (
SELECT e.*,
ROW_NUMBER() OVER ( PARTITION BY id_emp, id_year ORDER BY sales ) AS RN
FROM EMPLOYEE_SALES e
)
WHERE rn = 1
Query 2:
SELECT ID_EMP,
ID_YEAR,
MIN( SALES ) AS SALES,
LAG( MIN( SALES ) ) OVER ( PARTITION BY ID_EMP ORDER BY ID_YEAR ) AS PREVIOUS
FROM EMPLOYEE_SALES
GROUP BY ID_EMP, ID_YEAR
Results - Both give the same output:
| ID_EMP | ID_YEAR | SALES | PREVIOUS |
|--------|---------|-------|----------|
| 4 | 1 | 10 | (null) |
| 4 | 2 | 11 | 10 |

Answer 2

You mean like this?
select id_emp, id_year, min(sales) as min_sales,
lag(min(sales)) over (partition by id_emp order by id_year) as prev_year_min_sales
from facts
where id_emp = 4
group by id_emp, id_year;

Answer 3

I believe it is because you are using sales column in your group by statement.
Try to remove it and just use
GROUP BY id_emp,id_year

Answer 4

You could get your desired output using ROW_NUMBER() and LAG() analytic functions.
For example,
Table
SQL> SELECT * FROM t;
ID_EMP ID_YEAR SALES CLIENT_ID
---------- ---------- ---------- ----------
4 1 14 1
4 1 10 2
4 2 11 1
4 2 17 2
Query
SQL> WITH DATA AS
2 (SELECT t.*,
3 row_number() OVER(PARTITION BY id_emp, id_year ORDER BY sales) rn
4 FROM t
5 )
6 SELECT id_emp,
7 id_year ,
8 sales ,
9 lag(sales) over(order by sales) previous
10 FROM DATA
11 WHERE rn =1;
ID_EMP ID_YEAR SALES PREVIOUS
---------- ---------- ---------- ----------
4 1 10
4 2 11 10