SQL Server – Insert Multiple Values with UNIQUE Constraint

constraintinsertsql serversql-server-2012unique-constraint

I have a MS SQL Server 2012 and the following table:

CREATE TABLE dzp.contractid (
id bigint PRIMARY KEY IDENTITY(1,1),
VNR char(18) NOT NULL,
CONSTRAINT UC_VNR UNIQUE (VNR))

For context, VNR represents a unique contract number in string form.

I want to import a csv file with contract information, with possibly multiple rows per contract. To avoid querying over a char(18), I am trying to normalize the data upon loading using the INSERT-Trigger of the staging table.

Flow is:

csv-file --> staging table --> insert trigger --> normalized tables

In my trigger, I am attempting the following:

BEGIN TRY
    INSERT INTO dzp.contractid(VNR)
    SELECT VNR
    FROM dzp.accounts_stage
END TRY

BEGIN CATCH
-- ignore unique constraint violation error, raise otherwise
IF ERROR_NUMBER() <> 2627
    RAISERROR ('blah', 16, 1)
END CATCH

So what I hope to achieve is basically:

Get all the contract numbers from the staging table
Add all these numbers to the normalized table
Ignore the error that gets thrown when the unique constraint is violated
When working correctly, I now have a table with all the unique VNRs

Problem:

The Uniqueness-Constraint seems to be blocking the entire INSERT, not only the values that are actually duplicates.

Is there some way of inserting data row-wise, or tell the constraint to treat it on a row-by-row-basis?

Is this even the right approach? I'm happy to completely change the approach, since I cannot imagine I'm the first to have this issue… For context, this is essentially a reporting database that gets batch-fed once per day, with about 1m rows in total (from the csv-table), and has ~5 users running queries from time to time.

Thanks for your input!

Best Answer

SQL constraint violation affects the entire statement, you cannot ignore individual rows.

What you can do is insert only the rows that don't violate the constraint. There are several ways to do that, for example

INSERT INTO dzp.contractid(vnr)
SELECT DISTINCT vnr FROM dzp.accounts_stage s 
WHERE NOT EXISTS (SELECT 1 FROM dzp.contractid WHERE vnr = s.vnr)

You could also use MERGE:

MERGE dzp.contractid AS t
USING dzp.accounts_stage AS s
ON (t.vnr = s.vnr) 
WHEN NOT MATCHED BY TARGET 
THEN INSERT(vnr) VALUES(s.vnr)

Related Solutions

Sql-server – Unique Constraint with multiple null columns

I think your database is suffering from a bad data model. You might want to rethink it a little, judging from the tables you've mentioned the model isn't well normalized and you're trying to enforce a foreign key reference to a table column which isn't really a key to anything. One way to go is something like this :

CREATE TABLE EMP (ID INT PRIMARY KEY IDENTITY
                 ,EmpName VARCHAR(100) NULL)

CREATE TABLE PCTypes (id INT PRIMARY KEY IDENTITY
                     ,PcTypeName VARCHAR(100) NULL)

CREATE TABLE PC (Id INT PRIMARY KEY IDENTITY
                ,EmpId INT NULL
                ,PCName VARCHAR(100) NULL
                ,HostName VARCHAR(100) NULL
                ,PhysicalLocation VARCHAR(100) NULL
                ,PCType INT NULL)

ALTER TABLE PC ADD CONSTRAINT FK_PC_EmpId FOREIGN KEY (empId) REFERENCES Emp(id)
ALTER TABLE PC ADD CONSTRAINT FK_PC_PCType FOREIGN KEY (PCType) REFERENCES PCTypes(id)

CREATE TABLE PCNetwork (Id INT PRIMARY KEY IDENTITY
                       ,NetworkName VARCHAR(100) NULL
                       ,EmpId INT NULL
                       ,PhysicalLocation VARCHAR(100) NULL)

ALTER TABLE PCNetwork ADD CONSTRAINT FK_PCNetwork_EmpId FOREIGN KEY (empId) REFERENCES Emp(id)

CREATE TABLE PCNetwork_PCs (PCNetworkId INT NOT NULL
                           ,PCId INT NOT NULL
                           ,IPAddr NVARCHAR(20) NULL)

ALTER TABLE PCNetwork_PCs ADD CONSTRAINT FK_PCNetwork_PCs_Network FOREIGN KEY (PCNetworkId) REFERENCES PCNetwork(id)
ALTER TABLE PCNetwork_PCs ADD CONSTRAINT FK_PCNetwork_PCs_PC FOREIGN KEY (PCId) REFERENCES PC(id)
CREATE UNIQUE INDEX uq_pcnetworks ON PCNetwork_PCs(PCNetworkId, PCId)
CREATE UNIQUE INDEX uq_pcnetworks_ip ON PCNetwork_PCs(IPAddr)

Sql-server – Unique constraint on multiple nullable columns Sql Server

There's nothing special that would prevent you from using a standard unique constraint here, unless there's something you aren't telling us.

When a unique constraint is created on a set of nullable columns, NULL is treated (in terms of uniqueness) like any other of the distinct values in the set. (I believe this behaviour varies across RDBMSes.)

So I think the only case you might have to protect against here is the where all three columns contain NULL at the same time. If this is invalid for your business logic, also create a CHECK constraint to disallow this combination.

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