Question

I can get the results that I need, but I need a fast query.

id      value1      fid
1000    1203        5
1001    1293        1
1002    1203        3
1003    1211        1
1004    1263        1
1005    1223        5
1006    1243        2
1007    123         5
1008    1049        2
1009    1205        3

Here are the results that I need:

fid id      value1      id2     previous_value1
1   1004    1263        1003    1211
2   1008    1049        1006    1243
3   1009    1205        1002    1203
5   1007    123         1005    1223

Any ideas?

---

Edit: I forgot to wrote my query here is my query:

SELECT
t1.fid,
t1.id,
t1.value1,
t2.id AS id2,
t2.value1 AS previous_value1
FROM
(
  SELECT
  MAX(id) AS id
  FROM TABLENAME
  GROUP BY fid
) t3
INNER JOIN TABLENAME t1 ON t1.id = t3.id
INNER JOIN TABLENAME t2 ON t2.id = (SELECT id FROM TABLENAME WHERE id < t1.id AND fid =     t1.fid ORDER BY id DESC LIMIT 1)

Actually I simplified it by removing extra columns.

(There is 2 more columns in WHERE statement but it doesn’t matters.)

The original query takes ~0.04seconds. If I filter the results with the other two columns in where statement, it takes ~0.001 seconds.

Answer 1

Ok, here is a query that returns what you want (at least, what I think you want), but its anything but fast and efficient, so try it first:

SELECT  A.*, 
        (SELECT TOP 1 id FROM YourTable WHERE fid = A.fid AND id < B.MaxId ORDER BY id DESC) Id2,
        (SELECT TOP 1 value1 FROM YourTable WHERE fid = A.fid AND id < B.MaxId ORDER BY id DESC) previous_value1
FROM YourTable A
INNER JOIN (SELECT fid, MAX(id) Maxid
            FROM YourTable 
            GROUP BY fid) B
ON A.id = B.Maxid
ORDER BY A.fid