Unable To Create Unique Constraint On A NULL Column
Apr 5, 2004
Hi all,
I am trying to add a unique index/constraint on a column that allows NULL values. The column does have NULL values and when I try to create a unique constraint, I get the following error.
CREATE UNIQUE INDEX terminated because a duplicate key was found for index ID 9. Most significant primary key is '<NULL>'.
Are'nt you allowed to create a UNIQUE constraint on a NULL column? Books Online says that you are allowed to create a unique constraint on NULL columns, then why am I getting this error.
Can I create a unique constraint on a column that can contain null values? I need the control of the non null values (must be unique)...null is Ok if there's more than one. I tried creating a unique constraint but i'm getting the error (duplicate keys <null>)
After adding a Unique constraint to a database I cannot add more than one record with a null value for the constrained field. I've tried both adding the constraint to an empty table as well as a table with multiple null values already in the subject field; both efforts have failed.
According to BOL SQL-7 allows Unique Constraints on fields with Null values. Am I missing a step? I do need to allow nulls in the field yet ensure that when there is a non-null value it is unique.
The SQL statement I've used is: ALTER TABLE tbl_MasterUIC ADD CONSTRAINT uniquesamplenbr UNIQUE NONCLUSTERED (samplenbr)
I am attempting to create a unique constraint on an nvarchar field named theology (it is not the primary key field) that allows nulls. The table contains multiple rows with the value of null for field theology. The documentation says one can create a unique constraint on a field with all unique value except for null. Here is the error message:
'testtable1' table - Unable to create index 'IX_testtable1'. ODBC error: [Microsoft][ODBC SQL Server Driver][SQL Server]CREATE UNIQUE INDEX terminated because a duplicate key was found. Most significant primary key is ''. [Microsoft][ODBC SQL Server Driver][SQL Server]Could not create constraint. See previous errors.
Any ideas? I am creating a unique constraint and not a unique index. Is there some other database option to set to allow this?
why it is not possible to create a Foreign key to a Unique constraint?
Table A has column 1 holding a Primay key and two columns (2 and 3) holding a Unique combination (and some more columns).He created an Unique constraint on column 2 and 3 together.
He wanted to use this Unique combination to point to table B (instead of the table 1's PK) so he tried to create a foreign key on a column in table B but an error popped up prompting;
The columns in table 'TABLE_A' do not match an existing primary key or UNIQUE constraint.
Ok - these two columns ar no PK but the hold an Unique constraint......
I have a producer table with a nullable column that stores SSN's. In some cases producers inherit SSN's from other producers. These records will have a null producer.ssn and a record stored in a child table to track the inheritance. Anyway, I've found two techniques to enforce uniqueness on a nullable column and wanted to get opinions as to which was better. First, write a trigger. Second, create a computed column that has a unique constraint on it. The computed column would use the SSN if not NULL Else use the PK identity value of the record. EXAMPLE DML:CREATE TABLE test ( ssn CHAR(9) NULL, testId INT identity(1,1) NOT NULL, ComputedConstraint AS CASE WHEN ssn IS NULL THEN CAST(testId AS CHAR(9)) ELSE ssn END, UNIQUE (ComputedConstraint)) Any comments would be greatly appreciated.
I don't immediately find if this is possible but hope someone can give me an answer: is it possible to make a unique constraint over 2 columns but only when 1 column has a specific value ?
Example: table (tableid, instancetype, instancename, ..) instancetype can be A or B if it is A then instancename must be unique but for B instancename is not unique as these are copies from A
only solution I can think of is to make a trigger on an insert to check what the instancetype is and do a select to see if the name already exists in the table or not..
are there other solutions to make a constraint like this ?
Is it possible to create a unique constraint to a column from anothertable? For example:tb_current:current_names--------------aaabbbtb_new:new_name--------cccNow I want to create a constraint on tb_new.new_name to be unique withrespect to tb_current.current_names. However, tb_new.new_name shouldnot be unique to itself. So I should not be able to insert 'aaa' totb_new.new_name. But I should be able to insert 'ccc' totb_new.new_name.Here's the script to reproduce this example:create table tb_current(current_names varchar(10))create table tb_new(new_name varchar(10))insert tb_current values ('aaa')insert tb_current values ('bbb')insert tb_new values ('ccc')select * from tb_currentselect * from tb_newinsert tb_new values ('aaa') -- this should NOT be allowedinsert tb_new values ('ccc') -- this should be allowed
I have a table with one of its column VARBINARY(MAX).
I want to make sure that the values in this VARBINARY(MAX) column is unique. SQL Server doesn;t allow to create Unique Constraint over VARBINARY fields - whats the best workaround for ensuring uniqueness on VARBINARY columns.
We have a database where many tables have a field that has to be lengthened. In some cases this is a primary key or part of a primary key. The table in question is:-
/****** Object: Table [dbo].[DTb_HWSQueueMonthEnd] Script Date: 09/25/2014 14:05:09 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO SET ANSI_PADDING ON GO CREATE TABLE [dbo].[DTb_HWSQueueMonthEnd](
[Code] ....
The script I am using is
DECLARE@Column varchar(100)--The name of the column to change DECLARE@size varchar(5)--The new size of the column DECLARE @TSQL varchar(255)--Contains the code to be executed DECLARE @Object varchar(50)--Holds the name of the table DECLARE @dropc varchar(255)-- Drop constraint script
[Code] ....
When I the the script I get the error message Could not create constraint. See previous errors.
Looking at the strings I build
ALTER TABLE [dbo].[DTb_HWSQueueMonthEnd] DROP CONSTRAINT PK_DTb_HWSQueueMonthEnd ALTER TABLE [dbo].[DTb_HWSQueueMonthEnd] Alter Column [Patient System Number] varchar(10) ALTER TABLE [dbo].[DTb_HWSQueueMonthEnd] ADD CONSTRAINT PK_DTb_HWSQueueMonthEnd PRIMARY KEY NONCLUSTERED ([Patient System Number] ASC,[Episode Number] ASC,[CensusDate] ASC) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
They all seem fine except the last one which returns the error
Msg 8111, Level 16, State 1, Line 1 Cannot define PRIMARY KEY constraint on nullable column in table 'DTb_HWSQueueMonthEnd'. Msg 1750, Level 16, State 0, Line 1 Could not create constraint. See previous errors.
None of the fields I try to create the key on are nullable.
I want to enforce a unique constraint on a column which must be encrypted in MSSQL 2005 using Cell Level Encyption (CLE).
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'itsaSECRET!!!3£3£3£!!!' CREATE CERTIFICATE ERCERT WITH SUBJECT = 'A cert for use by procs' CREATE SYMMETRIC KEY ERKEY WITH ALGORITHM = AES_256 ENCRYPTION BY CERTIFICATE ERCERT
[Code] ....
The output makes it obvious why the constraint has 'not' been enforced.
I am having problems with unique contraint, say I have a table called customer create table customer ( id int identity(1,1) not null, name nvarchar(50) not null, id_card_no nvarchar(20) unique, ); so when I do mutilple null inserts insert into customer(name, id_card_no) values("Customer 1", NULL); insert into customer(name, id_card_no) values("Customer 2", NULL); I get an error duplicated keys on the unique column.
In Oracle DB, unique columns are behaved a little different where multiple nulls are allowed in a unique column.
I know there are some tircks that you can do to allow multiple nulls in unique column in sql server(well, pretend to be) like creating a computed column, create a view and an index...
Are there any ways to archieve that in sql sever compact?
I am having problems with unique contraint, say I have a table called customer create table customer ( id int identity(1,1) not null, name nvarchar(50) not null, id_card_no nvarchar(20) unique, ); so when I do mutilple null inserts insert into customer(name, id_card_no) values("Customer 1", NULL); insert into customer(name, id_card_no) values("Customer 2", NULL);
I get an error duplicated keys on the unique column. In Oracle DB, unique columns are behaved a little different where multiple nulls are allowed in a unique column.
I know there are some tircks that you can do to allow multiple nulls in unique column in sql server(well, pretend to be) like creating a computed column, create a view and an index...
Are there any ways to archieve that in sql sever compact?
Cannot find an answer to this in previous posting, though there are similar topics.
My primary key "ID" requires a value (is not nullable), and not explictly providing it with one when I update a new record gives the following error:
Cannot insert the value NULL into column 'ID', table 'AdClub.mediaq.News'; column does not allow nulls. INSERT fails. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Data.SqlClient.SqlException: Cannot insert the value NULL into column 'ID', table 'AdClub.mediaq.News'; column does not allow nulls. INSERT fails.
However, trying to stuff that field with a recordCount+1 value (or any value), I get this error:
Violation of PRIMARY KEY constraint 'Primary Key'. Cannot insert duplicate key in object 'News'. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Data.SqlClient.SqlException: Violation of PRIMARY KEY constraint 'Primary Key'. Cannot insert duplicate key in object 'News'.
Cannot figure this one out. The value I'm providing for that field is known to be unique, but the SQL Server spits it out each time.
Is there a way to have the ID primary field automatically update with a new value when a new record is generated? This is how I used to do it in Access, but cannot find a similar feature in SQL Server. I'm sure I'm missing something simple, but right now I'm stuck in this "Catch-22" situation.
To create a unique constraint on a multiple nullable column, we need to create a view with not null column and and then create a unique index on that view.
Hi, can anyone guide me on how to create a unique field with SqlExpress and VC#.net?
I know how to create primary key with identity, however I need to create another unique column for "email". I have search high and low for a solution but found none, the closest i got is unique constraint which I've not idea what's that.
Please help, else I have to always do a duplication check before inserting new records.
A UNIQUE INDEX must inherently impose a unique constraint and a UNIQUE CONSTRAINT is most likely implemented via a UNIQUE INDEX. So what is the difference? When you create in Enterprise Manager you must select one or the other.
What's the difference in the effect of the followings: CREATE UNIQUE NONCLUSTERED INDEX and ALTER TABLE dbo.titles ADD CONSTRAINT titleind UNIQUE NONCLUSTERED
I found there're two settings in Indexs/Keys dialog box of the management studio, Is Unique, and Type. The DDL statements above are generated by setting Is Unique to yes plus Type to Index, and just Type to Unique Key, respectively. What's the difference between them?
I'm a newby to SQL and looking for how-to-help. I have an existing DB and within a certain table, I have created a new Column via Studio manager, but need help with the following:
Need to make the new Col "Unique, and Indexed" but cannot see anywhere in studio manager interface to do it.
I am trying to create table with following SQL script:
Code Snippet
create table Projects( ID smallint identity (0, 1) constraint PK_Projects primary key, Name nvarchar (255) constraint NN_Prj_Name not null, Creator nvarchar (255), CreateDate datetime );
When I execute this script I get following error message:
Error source: SQL Server Compact ADO.NET Data Provider Error message: Named Constraint is not supported for this type of constraint. [ Constraint Name = NN_Prj_Name ]
I looked in the SQL Server Books Online and saw following:
CREATE TABLE (SQL Server Compact) ... < column_constraint > ::= [ CONSTRAINT constraint_name ] { [ NULL | NOT NULL ] | [ PRIMARY KEY | UNIQUE ] | REFERENCES ref_table [ ( ref_column ) ] [ ON DELETE { CASCADE | NO ACTION } ] [ ON UPDATE { CASCADE | NO ACTION } ]
As I understand according to documentation named constraints should be supported, however error message says opposite. I can rephrase SQL script by removing named constraint.
Code Snippet
create table Projects( ID smallint identity (0, 1) constraint PK_Projects primary key, Name nvarchar (255) not null, Creator nvarchar (255), CreateDate datetime ); This script executes correctly, however I want named constraints and this does not satisfy me.
We are using SQL CE 3.5 on tablet PCs, that synchs with our host SQL 2005 Server using Microsoft Synchronization Services. On the tablets, when inserting a record, we get the following error: A duplicate value cannot be inserted into a unique index. [ Table name = refRegTitle,Constraint name = PK_refRegTitle But the only PK on this table is RegTitleID.
The table structure is: [RegTitleID] [int] IDENTITY(1,1) NOT NULL, [RegTitleNumber] [int] NOT NULL, [RegTitleDescription] [varchar](200) NOT NULL, [FacilityTypeID] [int] NOT NULL, [Active] [bit] NOT NULL,
The problem occurs when a Title Number is inserted and a record with that number already exists. There is no unique constraint on Title Number. Has anyone else experienced this?
Hi everyone, I need urgent help to resolve this issue... As far as the performance goes which one is better.. Unique Index(col1, col2) OR Unique constraint(col1, col2) ? Unique constraint automatically adds a unique index and unique index takes care of uniqueness then whats the use of unique constraint ?
BOL says a unique constraint is preferred over a unique index. It also states that a unique constraint creates a unique index. What then is the difference between the two, and why is a constraint preferred over the index?
We have a vendor created database with 9000+ tables, one of which has about 6 billion rows. The vendor redesigned the database recently and ever since we've had terrible performance.
What the vendor did was increase any and all varchar columns (tens of thousands of columns) to 256.
Before the upgrade we had no problems creating an index on the 6billion row table, it would take 2 hours.
Now after the upgrade we've let the index creation command run for 5 days and killed it because it was consuming terabytes of logspace.
The previous design had combined column width of 1049 to what is now over 4000. The primary key itself is 1283 characters (SQL limit is 900).
There is no additional data, just wider columns. Why we are unable to create the index?
What is happening inside SQL Server? Does SQL make "room" in memory for the index for the entire width of the potential max row length?
