What's The Difference? Unque Constraint And Unique Index, Etc.?
Jul 23, 2005
All,
What's the difference between a unique contraint and unique?
sementically, if you want a column contain unique values, it is a
contraint. And an index is for searching/sort. The questions are:
1. Does a unique constraint interally use unique index?
2. If Yes to #1, I DO NOT need to create an index for search/sort
purpose, right?
3. If Yes to #2, What's better?
4. Also for Primary Key column, it is actually a special unique
contraint. Not need to create index on PK column for searching/sorting,
correct?
5. Also for FK contraint, no need to create an index for
searching/sorting?
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?
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?
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
When I add a unique key constraint to column in SQL 6.5 why does it alsocreate an index. e.g. In the table subaccounts I added a unique keyconstraint for the column login and SQL creates an index with the nameUQ_SubAccounts_2__19 (UKC).Does this also mean that there is no need to create an index for thiscolumn?thxMansoor
I am creating a new SSIS package where there is a flat file (CSV) I am importing. Well, there will be an end-user using a web UI to initiate the import of the file. However, this flat file is generated from another company and then uploaded to our network.
This flat file has the potential to have duplicate rows that would have already been imported at a previous date. With the constraints in the table, we have guaranteed that there will not be duplicates added, but the SSIS package fails immediately upon attempting to insert a duplicate row - and the bulk update is rolled back.
What I need to be able to do is load all of the rows that are not duplicates into the table. I am guessing that with my current approach, this is not possible. I am using a Data Flow task that converts the data in the flat file and then performs a bulk copy to load the data into the table.
How can I either ignore duplicate rows, or otherwise gracefully handle this data import?
When I create a unique constraint, SQL Server automatically creates an index on this constraint. So when I run the following...
ALTER TABLE PersonsProjects WITH NOCHECK ADD CONSTRAINT NoDupes UNIQUE NONCLUSTERED (PersonID, ProjectID)
...SQL Server will create a composite index on PersonsProjects called NoDupes on PersonIDand ProjectID. Thing is, I need this index to include a third column Status since most queries use this column in conjunction with PersonID and ProjectID. If there was no index on this table, I would have created it as follows:
CREATE UNIQUE INDEX NoDupes ON PersonsProjects (PersonID, ProjectID) INCLUDE (Status) WITH IGNORE_DUP_KEY
But this won't enforce the unique constraint on PersonID and ProjectID when performing inserts and updates. Is there any way of creating a unique constraint with an included column?
I would rather not have two indexes...
NoDupes: PersonID,ProjectID
New Index: PersonID,ProjectID INCLUDE Status
...so I'm trying to determine what other options that might be available...please advise.
I am really puzzled by an apparent difference between table index key column order and its statistics order. I was under understanding that index statistics mirror index definition. However, in my db 2470 index ordinal definitions match statistics definition but 66 do not. I also can reproduce such discrepancy in 2008 R2, 2012 and 2014.
As per definition,
stats_column_id int
1-based ordinal within set of stats columns
This script duplicates this for me.
BEGIN TRAN GO use tempdb GO CREATE TABLE [dbo].[ItemProperties]( [itmID] [int] NOT NULL, [cpID] [smallint] NOT NULL, [ipuID] [tinyint] NOT NULL,
We are on SQL 2014...we have a bunch of views in a database where we are trying to find the views which have more than 16 columns max for unique index/constraint...this is needed so we can convert them to indexed views...
please explain the differences btween this logical & phisicall operations that we can see therir graphical icons in execution plan tab in Management Studio
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?
Msg 2601, Level 14, State 1, Procedure DFP_report_load, Line 161 Cannot insert duplicate key row in object 'dbo.DFP_Reports_History' with unique index 'ix_report_history_creative_id'.
The duplicate key value is (40736326382, 1, 2015-07-03, 67618862, 355324). Msg 3621, Level 0, State 0, Procedure DFP_report_load, Line 161
The statement has been terminated.
Exception in Task: Cannot insert duplicate key row in object 'dbo.DFP_Reports_History' with unique index 'ix_report_history_creative_id'. The duplicate key value is (40736326382, 1, 2015-07-03, 67618862, 355324).
hi team, .Can i create umique constraint with out unique index.when i am creating a unique constraint sql creates a unique index (default) can i have only unique constraint ?
What 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.
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?
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))
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?
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.
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
