Fetch Max Value - sql

Question

TABLE Laptop_Shift_Departments
id Laptop_ID Curr_department Pre_Department
-----|----------|-----------------|----------------
9 71 4 3
10 68 4 3
11 71 5 4
12 68 5 4
User only search PO Number and against this PO_Num there are 2 laptops (Laptop_ID)
Above is my table now i want to get MAX value Against this laptop_ID ID
I have tried this:
SELECT LD.ID AS Laptop_ID,ld.GulfITBarcode,po.ID as PO_ID,PO.PO_Number as PO_Number,D.Department,
D.ID as Crr_DepID1,d2.Department,D2.ID as Pre_DepID2
FROM PO_PURCHASEORDER PO
INNER JOIN PO_Laptop_Master LM
ON LM.PO_ID = PO.ID
INNER JOIN PO_LaptopDetail LD
ON LD.LapTop_Master_ID = LM.ID
INNER JOIN Laptop_Shift_Departments DP
ON DP.Laptop_Detail_ID = LD.ID
inner join Laptop_Departments d
on d.ID = DP.Current_Dep_ID
inner join Laptop_Departments d2
on d2.ID = DP.Previous_Dep_ID
WHERE PO_NUMBER = '5258'
AND
LD.ID IN (select Max(cSh.id) from Laptop_Shift_Departments cSh)
But it is not working
MY output should be like this:
id Laptop_ID Curr_department Pre_Department
-----|----------|-----------------|----------------
11 71 5 4
12 68 5 4

Answer 1

You'll want to use the 'Group By' function at the end of the fields you want to group by and the 'Max' function in the Select on the columns you want the 'Max' (or 'Min' or 'Avg'). Should look something like this:
SELECT
LD.ID AS Laptop_ID
,ld.GulfITBarcode
,po.ID as PO_ID
,PO.PO_Number as PO_Number
,D.Department
,MAX(D.ID) as Crr_DepID1
,d2.Department
,MAX(D2.ID) as Pre_DepID2
FROM PO_PURCHASEORDER PO
INNER JOIN PO_Laptop_Master LM
ON LM.PO_ID = PO.ID
INNER JOIN PO_LaptopDetail LD
ON LD.LapTop_Master_ID = LM.ID
INNER JOIN Laptop_Shift_Departments DP
ON DP.Laptop_Detail_ID = LD.ID
inner join Laptop_Departments d
on d.ID = DP.Current_Dep_ID
inner join Laptop_Departments d2
on d2.ID = DP.Previous_Dep_ID
WHERE PO_NUMBER = '5258'
AND LD.ID IN (select Max(cSh.id) from Laptop_Shift_Departments cSh)
AND DP.Current_Dep_ID = 5
GROUP BY
LD.ID
,ld.GulfITBarcode
,po.ID
,PO.PO_Number
,D.Department
,d2.Department
(Having not seen the table structure I'm not sure as to the rest of the query. Hope this helps.)