How do I tell the query to only use distinct on only one field [duplicate] - sql

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This question already has answers here:
How do I select the first row per group in an SQL Query?
(8 answers)
Closed 12 months ago.
I'm attempting to pull a report from this table:
CREATE TABLE [Miscellaneous].[BackupStatus](
[BackupStatusId] [int] IDENTITY(1,1) NOT NULL,
[CompanyCode] [varchar](3) NOT NULL,
[ComputerName] [varchar](50) NOT NULL,
[DateTimeOfBackup] [datetime] NOT NULL,
[Description] [varchar](50) NOT NULL,
[IsSuccess] [bit] NOT NULL,
[Message] [nvarchar](max) NOT NULL,
[Exception] [nvarchar](max) NULL,
[ProgramDate] [datetime] NULL,
CONSTRAINT [PK_BackupStatus] PRIMARY KEY CLUSTERED
(
[BackupStatusId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
ALTER TABLE [Miscellaneous].[BackupStatus] ADD CONSTRAINT [DF_BackupStatus_IsSuccess] DEFAULT ((0)) FOR [IsSuccess]
GO
I need to get a list of most recent backup by CompanyCode. I only want the most recent record for each company (ie CompanyCode). I believe that I need to sort the table decending and distinct but I cannot figure it out.
SELECT Distinct CompanyCode, ComputerName, DateTimeOfBackup,
[Description], IsSuccess, [Message],
[Exception], ProgramDate, BackupStatusId
FROM Miscellaneous.BackupStatus
ORDER BY DateTimeOfBackup DESC
I'm getting back all records still. How do I tell the query to use distinct on only one field?
UPDATE
I hope to add some clarity to what I need.
In this case, it should only return records 4262 and 4266, since they are the most recent unique for that CompanyCode.

Answer 1

DISTINCT won't help here. You can use a windowed ROW_NUMBER() function to assign ordinals and then filter by ordinal = 1.
Something like:
SELECT CompanyCode, ComputerName, DateTimeOfBackup,
[Description], IsSuccess, [Message],
[Exception], ProgramDate, BackupStatusId
FROM (
SELECT
*,
ordinal = ROW_NUMBER() OVER(PARTITION BY CompanyCode ORDER BY DateTimeOfBackup DESC)
FROM Miscellaneous.BackupStatus
) A
WHERE A.Ordinal = 1 -- Just the latest
ORDER BY CompanyCode
This can also be coded using a CTE (common table expression):
WITH A AS (
SELECT
*,
ordinal = ROW_NUMBER() OVER(PARTITION BY CompanyCode ORDER BY DateTimeOfBackup DESC)
FROM Miscellaneous.BackupStatus
)
SELECT CompanyCode, ComputerName, DateTimeOfBackup,
[Description], IsSuccess, [Message],
[Exception], ProgramDate, BackupStatusId
FROM A
WHERE A.Ordinal = 1 -- Just the latest
ORDER BY CompanyCode