如何使用不同的标准两次使用相同的列和sql中的一个公共列

Question

I have a table

ID  P_ID  Cost
1   101   1000
2   101   1050
3   101   1100
4   102   5000
5   102   2000
6   102   6000
7   103   3000
8   103   5000
9   103   4000

I want to use 'Cost' column twice to fetch first and last inserted value in cost corresponding to each P_ID I want output as:

P_ID  First_Cost  Last_Cost
101    1000         1100
102    5000         6000
103    3000         4000

Answer 1

;WITH t AS 
(
  SELECT P_ID, Cost, 
    f = ROW_NUMBER() OVER (PARTITION BY P_ID ORDER BY ID),
    l = ROW_NUMBER() OVER (PARTITION BY P_ID ORDER BY ID DESC)
  FROM dbo.tablename
)
SELECT t.P_ID, t.Cost, t2.Cost
FROM t INNER JOIN t AS t2
ON t.P_ID = t2.P_ID
WHERE t.f = 1 AND t2.l = 1;

In 2012 you will be able to use FIRST_VALUE() :

SELECT DISTINCT
  P_ID, 
  FIRST_VALUE(Cost) OVER (PARTITION BY P_ID ORDER BY ID),
  FIRST_VALUE(Cost) OVER (PARTITION BY P_ID ORDER BY ID DESC)
FROM dbo.tablename;

You get a slightly more favorable plan if you remove the DISTINCT and instead use ROW_NUMBER() with the same partitioning to eliminate multiple rows with the same P_ID :

;WITH t AS
(
  SELECT
   P_ID, 
   f = FIRST_VALUE(Cost) OVER (PARTITION BY P_ID ORDER BY ID),
   l = FIRST_VALUE(Cost) OVER (PARTITION BY P_ID ORDER BY ID DESC),
   r = ROW_NUMBER() OVER (PARTITION BY P_ID ORDER BY ID)
  FROM dbo.tablename
)
SELECT P_ID, f, l FROM t WHERE r = 1;

Why not LAST_VALUE() , you ask? Well, it doesn't work like you might expect. For more details, see the comments under the documentation .

Answer 2

SELECT t.P_ID, 
  SUM(CASE WHEN ID = t.minID THEN Cost ELSE 0 END) as FirstCost,
  SUM(CASE WHEN ID = t.maxID THEN Cost ELSE 0 END) as LastCost
FROM myTable
JOIN (
  SELECT P_ID, MIN(ID) as minID, MAX(ID) as maxID
  FROM myTable
  GROUP BY P_ID) t ON myTable.ID IN (t.minID, t.maxID)
GROUP BY t.P_ID

Admittedly, @AaronBertrand's approach is cleaner here. However, this solution will work on older versions of SQL Server (that don't support CTE's or window functions), or on pretty much any other DBMS.

Answer 3

Do you want first and last in terms of Min and Max, or do you want which one was entered first and which one was entered last? If you want Min and max you can group by.

SELECT P_ID, MIN(Cost), MAX(Cost) FROM table_name GROUP BY P_ID

Answer 4

I believe this does your thing also, just without self joins or subqueries:

SELECT DISTINCT
   P_ID
  ,MIN(Cost) OVER (PARTITION BY P_ID) as FirstCost
  ,MAX(Cost) OVER (PARTITION BY P_ID) as LastCost
FROM Table