Sql-server – Why does this UPDATE fail with a unique key constraint violation

constraintsql serverunique-constraintupdateview

I'm an "accidental" DBA, relatively inexperienced and baffled by this problem.

Running MS SQL Server 2012. The problem is with this UPDATE statement:

UPDATE dbo.tAccts SET
       Ticket               = 'ARP.ExGE'
       , Method             = 'smtp'
       , AcctOwner          = 'r00417819'
       , DisplayName = '~AppLight HBSFax-Inactive'
       , Destination = 'r00417819@mail.ad.ge.com'
       , UpdatedBy          = SYSTEM_USER
       , UpdatedOn          = CAST(GetDate() AS DATE)
FROM dbo.vReclaimable
WHERE OHR_EmpStatus <> 'A'

Which should update only the rows in the tAccts table which are returned by the vReclaimable view.

The vReclaimable view is based on the tAccts table and returns a subset of the rows in tAccts.

When I run it, it fails with a unique key error:

(0 row(s) affected)
Msg 2627, Level 14, State 1, Line 67
Violation of UNIQUE KEY constraint 'UQ__tAccounts_DNIS.Method.Destination.Phones'. Cannot insert duplicate key in object 'dbo.tAccts'. The duplicate key value is (68497, smtp, r00417819@mail.ad.ge.com, 800-905-8793, none).
The statement has been terminated.

Fair enough, the tAccts table does have a unique key constraint:

CONSTRAINT [UQ__tAccounts_DNIS.Method.Destination.Phones] UNIQUE NONCLUSTERED 
(
                [DNIS] ASC,[Method] ASC,[Destination] ASC,[Phone_TF] ASC,[Phone_Local] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON)

But here’s the weird thing. If I run these two queries:

select 'tAccts table', dnis, method, destination, phone_tf, phone_local from tAccts where dnis=68497
select 'vReclaimable view', dnis, method, destination, phone_tf, phone_local, daysidle from vReclaimable where dnis=68497

The first returns two rows (as expected):

(No column name)     dnis   method destination   phone_tf      phone_local
tAccts table  68497  ftp    ftp://faxuser@ap1plm02cige/appliances    800-905-8793  none
tAccts table  68497  unc    \\\\for4as01applge\\cfs_portfolio\\cfs_faxdocs  800-905-8793  none

and the second returns 0 rows (as expected).

If “FROM vReclaimable WHERE OHR_EmpStatus <> ‘A’” returns 0 rows, why is the UPDATE trying to update the row where DNIS=68497?

(I hope I've described this adequately. I've a feeling I'm missing something obvious)

USE [TEST-GEAFax_arley_NEW]
GO

/****** Object:  Table [dbo].[tAccts]    Script Date: 12/9/2015 1:39:41 PM ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[tAccts](
    [Ticket] [varchar](30) NOT NULL,
    [Method] [varchar](15) NOT NULL,
    [AcctOwner] [varchar](15) NOT NULL,
    [DisplayName] [varchar](75) NOT NULL,
    [Destination] [varchar](75) NOT NULL,
    [DNIS] [varchar](20) NOT NULL,
    [DNIS2] [varchar](20) NULL,
    [Phone_TF] [varchar](30) NOT NULL,
    [Phone_Local] [varchar](30) NOT NULL,
    [Phone_PBX] [varchar](255) NOT NULL,
    [UpdatedBy] [varchar](50) NOT NULL,
    [UpdatedOn] [date] NOT NULL,
    [FaxNotes] [varchar](255) NULL,
    [TelcomNotes] [varchar](255) NULL,
    [AcctID] [int] IDENTITY(0,1) NOT NULL,
 CONSTRAINT [PK__tAccounts_AcctID] PRIMARY KEY CLUSTERED 
(
    [AcctID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY],
 CONSTRAINT [UQ__tAccounts_DNIS.Method.Destination.Phones] UNIQUE NONCLUSTERED 
(
    [DNIS] ASC,
    [Method] ASC,
    [Destination] ASC,
    [Phone_TF] ASC,
    [Phone_Local] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

---------------------------------------------------------------------------------

USE [TEST-GEAFax_arley_NEW]
GO

/****** Object:  View [dbo].[vReclaimable]    Script Date: 12/9/2015 1:39:57 PM ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO


/***********************************************************************
* Written By    : N. Arley Dealey (200018252
* Written On    :
* Updated By    :
* Updated On    :
* Description   : Returns data from tAccts, vRxAl, vWLT_AllGE
* Notes         :
***********************************************************************/
CREATE VIEW [dbo].[vReclaimable] AS
SELECT
        a.Ticket
        , a.Method
        , a.AcctOwner
        , a.DisplayName
        , a.Destination
        , a.DNIS
        , a.DNIS2
        , a.Phone_TF
        , a.Phone_Local
        , a.Phone_PBX
        , a.UpdatedBy
        , a.UpdatedOn
        , a.FaxNotes
        , a.TelcomNotes
        , a.AcctID
        , COUNT(jt.JobID) AS 'FaxesRcvd'
        , CAST(MIN(jt.TimeStamp_UTC) AS DATE) AS 'FirstRcvd'
        , CAST(MAX(jt.TimeStamp_UTC) AS DATE) AS 'LastRcvd'
        , DATEDIFF(dd, MAX(jt.TimeStamp_UTC), GETDATE()) AS 'DaysIdle'
        , o.OHR_EmpSSO
        , o.OHR_EmpStatus
        , o.OHR_EmpName
        , o.OHR_EmpTitle
        , o.OHR_BizIndustryGroup
        , o.OHR_BizSegment
        , o.OHR_BizUnit
        , o.OHR_BizDept
        , o.OHR_BizDomain
FROM
    dbo.tAccts AS a
    LEFT OUTER JOIN dbo.tAccts_Retain AS r ON (a.AcctID = r.AcctID)
    LEFT OUTER JOIN dbo.vWLT_AllGE AS o ON (a.AcctOwner = o.OHR_EmpSSO)
    LEFT OUTER JOIN dbo.vRxAll AS jt ON (a.DNIS = jt.DNIS)
    WHERE ( 1                                               -- place holder, has no effect
            AND r.RetainID IS NULL                          -- out of scope: in Retain table
            AND a.Method = 'smtp'                           -- out of scope: ftp, unc, cifs, printers
            AND a.Phone_Local NOT LIKE '216-%'              -- out of scope: NELA numbers
            AND a.AcctOwner <> 'r00417819'                  -- out of scope: reclaimed numbers
            AND a.AcctOwner <> 'r00336832'                  -- out of scope: never assigned numbers
            AND a.AcctOwner <> 'r00971729'                  -- out of scope: invalid numbers
            AND a.Destination NOT LIKE 'g%@mail.ad.ge.com'  -- out of scope: distribution lists
            AND a.Destination NOT LIKE 'r%@mail.ad.ge.com'  -- out of scope: shared mailboxes
        )
    GROUP BY
        a.DNIS
        -- remaining columns are just for syntax reasons
        , a.Ticket, a.Method, a.AcctOwner, a.DisplayName, a.Destination, a.DNIS2, a.Phone_TF, a.Phone_Local, a.Phone_PBX, a.UpdatedBy, a.UpdatedOn, a.FaxNotes, a.TelcomNotes, a.AcctID
        , o.OHR_EmpSSO, o.OHR_EmpStatus, o.OHR_EmpName, o.OHR_EmpTitle
        , o.OHR_BizIndustryGroup, o.OHR_BizSegment, o.OHR_BizUnit, o.OHR_BizDept, o.OHR_BizDomain

GO

Best Answer

It boils down to what UPDATE statement does. It's not entirely obvious but your statement is equivalent to this one:

UPDATE upd SET
         Ticket             = 'ARP.ExGE'
       , Method             = 'smtp'
       , AcctOwner          = 'r00417819'
       , DisplayName = '~AppLight HBSFax-Inactive'
       , Destination = 'r00417819@mail.ad.ge.com'
       , UpdatedBy          = SYSTEM_USER
       , UpdatedOn          = CAST(GetDate() AS DATE)
FROM 
    dbo.tAccts AS upd 
  CROSS JOIN
    dbo.vReclaimable AS v
WHERE OHR_EmpStatus <> 'A' ;

Since there is no mention of the dbo.tAccts table in the FROM and no join or where condition between the table and the view, it results in a CROSS join and an attempt to update all rows of the table (and not just from the view), and probably multiple times as well!

You can add a join (or where) condition with:

UPDATE upd SET
         Ticket             = 'ARP.ExGE'
       , Method             = 'smtp'
       , AcctOwner          = 'r00417819'
       , DisplayName = '~AppLight HBSFax-Inactive'
       , Destination = 'r00417819@mail.ad.ge.com'
       , UpdatedBy          = SYSTEM_USER
       , UpdatedOn          = CAST(GetDate() AS DATE)
FROM 
    dbo.tAccts AS upd 
  JOIN
    dbo.vReclaimable AS v
      ON v.PK = upd.PK              -- whatever the PK column is
WHERE OHR_EmpStatus <> 'A' ;

or (using your version):

UPDATE dbo.tAccts SET
       Ticket               = 'ARP.ExGE'
       , Method             = 'smtp'
       , AcctOwner          = 'r00417819'
       , DisplayName = '~AppLight HBSFax-Inactive'
       , Destination = 'r00417819@mail.ad.ge.com'
       , UpdatedBy          = SYSTEM_USER
       , UpdatedOn          = CAST(GetDate() AS DATE)
FROM dbo.vReclaimable
WHERE OHR_EmpStatus <> 'A'
  AND vReclaimable.PK = tAccts.PK ;

Alternatively, you can (probably) simply update the view. For this to be working, the view has to conform with the limitations about "Updatable Views". See the relevant paragraph at MSDN documentation: CREATE VIEW, Updatable Views:

UPDATE dbo.vReclaimable SET
       Ticket               = 'ARP.ExGE'
       , Method             = 'smtp'
       , AcctOwner          = 'r00417819'
       , DisplayName = '~AppLight HBSFax-Inactive'
       , Destination = 'r00417819@mail.ad.ge.com'
       , UpdatedBy          = SYSTEM_USER
       , UpdatedOn          = CAST(GetDate() AS DATE)

WHERE OHR_EmpStatus <> 'A' ;

Related Solutions

Sql-server – Unexpected Unique Constraint Violation

Why not just collate that column as case-sensitive? I don't think you need to resort to binary. This seems to work fine, just note that it may affect sorting, comparisons, unions etc:

CREATE TABLE [dbo].[Unit]
(
    [id]                SMALLINT       NOT NULL IDENTITY(1,1),
    [name]              VARCHAR(100)   COLLATE Latin1_General_CS_AS NOT NULL ,

    CONSTRAINT [PK_Unit] PRIMARY KEY CLUSTERED ([id]),
    CONSTRAINT [UQ_Unit_Name] UNIQUE ([name])
);
GO

INSERT INTO dbo.Unit (Name) VALUES('e³m³/day') 
INSERT INTO dbo.Unit (Name) VALUES('e3m3/day')

Results:

1 row(s) affected.
1 row(s) affected.

Now, this works for the example in your question, but whether it works for your entire set of requirements, is hard to say. You may have characters that are different to you but aren't treated differently in terms of case-sensitivity, such as:

INSERT INTO dbo.Unit (Name) VALUES('ß')
INSERT INTO dbo.Unit (Name) VALUES('ss')

Results:

1 row(s) affected.

And then:

Msg 2627, Level 14, State 1, Line 2
Violation of UNIQUE KEY constraint 'UQ_Unit_Name'. Cannot insert duplicate key in object 'dbo.Unit'. The duplicate key value is (ss).
The statement has been terminated.

In that case you may need to use binary after all.

Sql-server – UNIQUE index key violation

There is a lot to grasp if you want to fully understand all of the intricacies of locking and isolation levels in SQL Server, and your question is essentially leading you in this direction.

All of the information is available at http://msdn.microsoft.com/en-us/library/ms173763.aspx, although it's not an easy read. An easier read is available at http://databases.about.com/od/sqlserver/a/isolationmodels.htm - pay particular attention to the "phantom reads" section.

For what you are trying to do you would need BOTH transactions running with an isolation level of "SERIALIZABLE". What this basically means is that they will run "as if" one was run after the other - that they were actually serialized.

What is happening is that BOTH the transactions decide that the same record needs to be inserted, and then BOTH try to insert that same record. The lock that is taken by the test logic is separate from the lock that is taken for the insert, which allows this to happen. SERIALIZABLE will stop this from happening with it's "Other transactions cannot insert new rows with key values that would fall in the range of keys read by any statements in the current transaction until the current transaction completes" clause. Another way to think of this is that the read locks from the test need to be held until the whole transaction completes. This can be specified using a HOLDLOCK query hint; but I have to say that I've not personally played with using HOLDLOCK, but just with the "SET TRANSACTION ISOLATION LEVEL SERIALIZABLE" version.

Best Answer

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Sql-server – Unexpected Unique Constraint Violation

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