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)
Thanks for any and all suggestions
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.
Any help would be appreciated.
Thanks,
Amir
Why we the Unique Constraint doesn't allow the multiple null values in Sql Server?
View 2 Replies View RelatedA 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.
View 8 Replies View RelatedHelloWhat should I use for better perfomance sinceunique constraint always use index ?ThanksKamil
View 5 Replies View RelatedWhat'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?
Hi, all.
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 ?
Which one do one use ?
thanks
sonali
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?
View 2 Replies View RelatedHi,I want to add unique contraint to EXISTING column in EXISTING table.I have ms sql 2005.How to do that?
View 7 Replies View RelatedDoes anyone have any Idea on how I could enforce a unique constrait across multiple tables?
View 1 Replies View RelatedWhat is the simplest way to add a unique constraint on a field of type varchar(7) that can allow any number of <NULL>'s?
I only want to ensure that when this field is updated, it is updated with a value that has not been used.
IF EXISTS (SELECT Project FROM tbProjects WHERE Project = @cProject)
RAISERROR('Project number already used!',16,1)
ELSE
UPDATE tbProjects SET Project = @cProject WHERE ProjectID = @iProjectID
GO
Also, I cannot allow the user to chante the project field value once it is set.
Any suggestions?
Mike B
Anybody knows how to make two columns in a table unique?
View 1 Replies View Relatedi'm just creating a table, no data as yet.
i have a varchar(15) fld with Nulls NOT allowed
i want to create a constraint that this field named ipkey be UNIQUE.
I'm having trouble with the syntax for the constraint expression.
i've typed in the SQL Server Managment Studio Express Expression field:
UNIQUE(ipkey)
and
@unq_ipkey UNIQUE(ipkey)
SQL Server Managment Studio Express complains:
"Error validating constrating, do you want to edit expression"
So - what am i doing wrong?
And thanks for taking the time to help.
Hi,
I have a table with two column, c1 and c2. c1 is set as primary key. I want c2 to be set with unique constraint.
I choose this talbe in object explorer, right click and select modify. Then I choose "index/key" from "table designer" menu.
The problem is that in the "index/key" dialog, the "Columns" item (under General) is always c1. if I click the "..." button to popup "index column", I could only choose either "c1" or <None> under "column name" dropdownlist.
How could I choose c2 and set unique constraint on it?
Thx
Tao
Hi,
I need to define a constraint , to prevent some fields of a table to be duplicated, How can i define this constraint ?
Here is the table I created:
create table Test (
[recId] [int] identity(1, 1) not null,
[code] [varchar](50) not null,
[prime] [bit] not null constraint [DF_Test_prime] default (cast(0 as bit)),
constraint [PK_Test] primary key clustered
(
[recId]
) with fillfactor = 90 on [primary]
) on [primary]
go
insert into Test (code, prime) values ('AVA', cast(1 as bit))
insert into Test (code, prime) values ('BUS', cast(1 as bit))
insert into Test (code, prime) values ('BUS', cast(0 as bit))
insert into Test (code, prime) values ('BUS', cast(0 as bit))
insert into Test (code, prime) values ('CAR', cast(1 as bit))
insert into Test (code, prime) values ('CAR', cast(0 as bit))
insert into Test (code, prime) values ('RLW', cast(1 as bit))
insert into Test (code, prime) values ('RLW', cast(0 as bit))
insert into Test (code, prime) values ('RLW', cast(0 as bit))
select *
from Test
I need to create a constraint on this table that will not allow me to have two rows that are prime for the same code. So the following insert statement should fail:
-- This should fail
insert into Test (code, prime) values ('RLW', cast(1 as bit))
Thanks for you help!
Regards,
Anand
Hi All,
I am trying to catch a specfic unique key constraint in a table.
i my table i have two fields USERID And EMAILID and i set both to unique.
now on registration form i am checking that USERID or EMAIID is already present or not.
by taking ex.number =2627 i am not able to find which unique key constraint is getting violated.
is there any other way to find it.
thanks in advance.
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?
.
when we use Unique constraint over a column it allows null values.
but then null values are duplicating, how is that?
thanks
Hi All:
Is there a way to create a unique constraint with 4 fields combined, such as colA, colB, colC, and colD.
but colD is for all the values but value = 3.
If this does not work out, trigger probably is the last way I would like to approach. and it is slower than constraint with many inserts.
thanks
David
I want to add a unique constraint on 3 fields, to only allow the value in the field ONE time. The value will NEVER be the same for anything else. This is the table structure
Code:
Create Table Employees
(
P_Id int NOT NULL,
InstructorName varchar(255) NOT NULL,
CourseName varchar(100) NOT NULL,
DataTableName varchar(100) NOT NULL
)
I want to create a unique constraint across the fields Instructorname, CourseName, DataTableName as their is ONLY 1 instructor per course per table so those 3 fields will ALWAYS hold unique values. I think the constraint syntax would go like so, but want to check before I go butchering some sql syntax.
constraint syntax:
Code:
Alter Table Employees
Contstraint uniqueEmployee Unique (InstructorName ,CourseName ,DataTableName )
I'm trying to weight the pros and cons of unique constraints and unique indexes. I understand that creating a unique constraint also creates an index. If that is the case, why not just use a unique index? Could someone give me an example of when you would want an unique constraint over an unique indexes
Thanks in advance
What is the difference between unqiue constraint and unique index? What are the pros and cons? Are they interchangable?
------------------------
I think, therefore I am - Rene Descartes
hi
i create a sample table by this code and insert some values to it :
create table test(
c1 int,
c2 int)
insert test select 1,2
insert test select 2,44
insert test select 3,56
now, i want to add new column with unique constraint by this code :
alter table test
add c3 int unique
but the following error has shown me :
Msg 1505, Level 16, State 1, Line 1
CREATE UNIQUE INDEX terminated because a duplicate key was found for object name 'dbo.test' and index name 'UQ__test__2D27B809'. The duplicate key value is (<NULL>).
Msg 1750, Level 16, State 0, Line 1
Could not create constraint. See previous errors.
The statement has been terminated.
where does my problem and how to solve it ?
thaniks
Hello...
I was confused with UNIQUE key. Its easy to create PRIMARY KEY to the Table. Now how to alter the Table to have UNIQUE key...
Thanks
Ganesh
Solutions are easy. Understanding the problem, now, that's the hard part
I like to use the management console to design tables, but have
been unable to figure out how to add a unique column constraint.
I have a primary key defined in col1 and want to make col2, char(10),
unique, but keep col1 as the primary key.
I have tried the Check constraint menu path, but do not know how
to write the expression.
If I go along the Indexes/Key path, I am forced to change the primary
key which I do not want to do.
Can anyone help?
TIA, Joe
I have a table called tblImages with the following columns:
ImageID [int]
UserID [int]
MainImg [bit]
what i need to ensure is that only one MainImage can be = 1 (true) for each userId at any one time.
any idea what i need to do?
alex
I'm trying to clean-up certain Phone Types and I need to update Phone Types system wide, but certain constraints are holding me back...I'm just getting the error:
Violation of UNIQUE KEY constraint 'IX_co_customer_x_phone'. Cannot insert duplicate key in object 'co_customer_x_phone'.
The statement has been terminated. Strange thing is I can add certain statements to my where clause to find an exact customer and change their phone type, but when I want to change the phone type system wide I get this error.
update co_customer_x_phone
set cph_pht_key = '47961833-C53A-4223-8229-4453350934F7'
FROM co_customer_x_phone (NOLOCK)
LEFT JOIN co_phone_type (NOLOCK)
on pht_key = cph_pht_key
JOIN co_customer cst (NOLOCK)
ON cph_cst_key = cst.cst_key
JOIN co_phone (NOLOCK)
ON cph_phn_key=phn_key
where cph_pht_key='2E486DF9-7A16-47F6-83BA-A304746F50DE'
how can i apply unique cosntraint in an existing table's column
i want to do it like this as below
sql server enterprise manager ==> DB==>table (R.click)==>design table
Is it possible to create a unique constraint on two tables?In mssql2000?
View 7 Replies View Related