Question

I have the table of DeviceMaster and DeviceStatus.
where in DeviceMaster is the master for devices and the DeviceStatus is the status of the device.Now i want to get the record of the latest DeviceStatus of each device with only one row using the DeviceMasterId and according to the last one first(descending order).

eg.

 DeviceName       RecordCreatedDate        Status
ElectronicRod     14/11/2011 12:00:00       On
ElectronicRod     14/11/2011 11:30:00       Off

even though the there is multiple record in DeviceStatus.

here is the table structure

DeviceMaster

[Id] [int],
[ROId] [int] ,
[ClientId] [int] ,
[DeviceTypeId] [int] ,
[Label] [varchar](50) ,
[ClientCommChannelId] [int] ,
[ServerCommChannelId] [bigint] ,
[DeviceName] [varchar](50) ,
[Address] [varchar](50) ,
[Attribute1] [varchar](50) ,
[Attribute2] [varchar](50) ,
[Attribute3] [varchar](50) ,
[IsDeleted] [bit] ,
[RecordCreatedDate] [datetime] ,
[RecordUpdatedDate] [datetime] ,
[RecordCreatedBy] [int] ,
[RecordUpdatedBy] [int] ,
[IsTransfered] [bit]

DeviceStatus

[Id] [bigint],
[ROId] [int],
[ClientId] [int],
[ServerDeviceId] [bigint] , --It is the foreign key reference of Device Id
[ClientDeviceId] [int] ,
[Status] [bit] ,
[TimeStamp] [datetime] ,
[Attribute1] [varchar](50) ,
[Attribute2] [varchar](50) ,
[Attribute3] [varchar](50) ,
[RecordCreatedDate] [datetime] ,
[RecordUpdatedDate] [datetime] ,
[RecordCreatedBy] [int] ,
[RecordUpdatedBy] [int] ,
[IsTransfered] [bit]

DeviceStatus have the multiple line entry for single device.I need the latest DeviceStatus for each and every device.

Thank you in advance

Answer 1

You can use a CTE (Common Table Expression) with the ROW_NUMBER function:

;WITH LastPerDevice AS
(
   SELECT 
       dm.DeviceName, ds.RecordCreatedDate, ds.Status,
       ROW_NUMBER() OVER(PARTITION BY dm.DeviceMasterId 
                         ORDER BY ds.RecordCreatedDate DESC) AS 'RowNum'
   FROM dbo.DeviceMaster dm
   INNER JOIN dbo.DeviceStatus ds ON ds.DeviceMasterId = dm.DeviceMasterId 
)
SELECT 
   DeviceName, RecordCreatedDate, Status
FROM LastPerDevice
WHERE RowNum = 1

This CTE “partitions” your data by DeviceMasterId, and for each partition, the ROW_NUMBER function hands out sequential numbers, starting at 1 and ordered by RecordCreatedDate DESC – so the most recent row gets RowNum = 1 (for each DeviceMasterId) which is what I select from the CTE in the SELECT statement after it.