What is the best way to generate Id or Code column(primary key) in a table in SQL Server? My requirement is a big table which stores more than 1000000 rows.
So generally we create auto identity column of a table but is it the best way? For example, I have an employee_master table and there are three columns like
emp_id auto increment
Emp_code varchar(20)
and also default like Rowno of a table.
So in this scenario, it has 3 unique columns of a table. Is it the best way?
Or what is the best way to generate id/code column both master and transaction table.
Also is there any way which we generate financial year wise auto-generate column.(any function)
The following SQL statement defines the "ID" column to be an auto-increment primary key field in the "Persons" table
CREATE TABLE Persons (
ID int NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
PRIMARY KEY (ID)
);
I think this will work..
I need to design a table in SQL Server having some columns, one of these columns (ID column and use sequential uniqueidentifier) should automatically populate its data when inserting other column data.
The values of the ID column should be generated automatically when insertion happens.
Please help me to do this, any help is appreciated.
NB: I am new to this step by step approach will be more helpful
Just create a table with a column ID of datatype uniqueidentifier and set it's default value to newsequentialid():
Then, when you go insert rows into that table, just omit the ID column from the list of columns you're inserted values into:
INSERT INTO dbo.YourTable(ColA, ColB, ....., ColX)
VALUES(.., .. ,. ...)
If you don't explicitly insert a value into ID, the default specification (newsequentialid()) will be used .
As per Marc_s's comment, you should use NEWSEQUENTIALID()
CREATE TABLE myTable (ColumnA uniqueidentifier DEFAULT NEWSEQUENTIALID());
See NEWSEQUENTIALID (Transact-SQL)
I am having a column named no. If I insert the no in database same no should not insert, if it is stored in that table. please help me.
Thank you
Make the required column unique using UNIQUE constraint.
Your create table statement should be like:
CREATE TABLE table_name ( col_1 datatype UNIQUE, col_2 datatype, .....)
This makes col_1 unique.
set it as Unique column and auto-increment.
A look on Google returns Sql learning Basics and this
You can set your column auto increment property to on it will enable the column to add a unique incremental value for each new record other way to is add a primary key or unique key constraint to that particular column
Thanks
I've got a table that collects forms submitted from our website, but for some reason, when they created the table, they didn't put a timestamp in the table. I want it to enter the exact date and time that the record was entered.
I know it's in there somewhere, but I can't seem to find how to set the default value (like in Access, you use getNow() or Now()) but I don't know where to put it.
For modifying an existing column in an existing table:
ALTER TABLE YourTable ADD CONSTRAINT DF_YourTable DEFAULT GETDATE() FOR YourColumn
This can also be done through the SSMS GUI.
Put your table in design view (Right click on table in object explorer->Design)
Add a column to the table (or click on the column you want to update if it already exists)
In Column Properties, enter (getdate()) in Default Value or
Binding field as pictured below
In that table in SQL Server, specify the default value of that column to be CURRENT_TIMESTAMP.
The datatype of that column may be datetime or datetime2.
e.g.
Create Table Student
(
Name varchar(50),
DateOfAddmission datetime default CURRENT_TIMESTAMP
);
While the marked answer is correct with:
ALTER TABLE YourTable ADD CONSTRAINT DF_YourTable DEFAULT GETDATE() FOR YourColumn
You should always be aware of timezones when adding default datetime values in to a column.
Say for example, this datetime value is designed to indicate when a member joined a website and you want it to be displayed back to the user, GETDATE() will give you the server time so could show discrepancies if the user is in a different locale to the server.
If you expect to deal with international users, it is better in some cases to use GETUTCDATE(), which:
Returns the current database system timestamp as a datetime value. The database time zone offset is not included. This value represents the current UTC time (Coordinated Universal Time). This value is derived from the operating system of the computer on which the instance of SQL Server is running.
ALTER TABLE YourTable ADD CONSTRAINT DF_YourTable DEFAULT GETUTCDATE() FOR YourColumn
When retrieving the values, the front end application/website should transform this value from UTC time to the locale/culture of the user requesting it.
Disallow Nulls on the column and set a default on the column of getdate()
/*Deal with any existing NULLs*/
UPDATE YourTable SET created_date=GETDATE() /*Or some sentinel value
'19000101' maybe?*/
WHERE created_date IS NULL
/*Disallow NULLs*/
ALTER TABLE YourTable ALTER COLUMN created_date DATE NOT NULL
/*Add default constraint*/
ALTER TABLE YourTable ADD CONSTRAINT
DF_YourTable_created_date DEFAULT GETDATE() FOR created_date
The syntax for this when creating a new table is:
CREATE TABLE MyTable
(
MYTableID INT IDENTITY(1,1),
CreateDate DATETIME NOT NULL CONSTRAINT DF_MyTable_CreateDate_GETDATE DEFAULT GETDATE()
)
This works for me...
ALTER TABLE [accounts]
ADD [user_registered] DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ;
This also works:
CREATE TABLE Example(
...
created datetime default GETDATE()
);
Or:
ALTER TABLE EXAMPLE ADD created datetime default GETDATE();
This worked for me. I am using SQL Developer with Oracle DB:
ALTER TABLE YOUR_TABLE
ADD Date_Created TIMESTAMP DEFAULT CURRENT_TIMESTAMP NOT NULL;
Let's say you create a database table for a registration system.
IF OBJECT_ID('dbo.registration_demo', 'U') IS NOT NULL
DROP TABLE dbo.registration_demo;
CREATE TABLE dbo.registration_demo (
id INT IDENTITY PRIMARY KEY,
name NVARCHAR(8)
);
Now a couple people register.
INSERT INTO dbo.registration_demo (name) VALUES
('John'),('Jane'),('Jeff');
Then you realize you need a timestamp for when they registered.
If this app is limited to a geographically localized region, then you can use the local server time with GETDATE(). Otherwise you should heed Tanner's consideration for the global audience with GETUTCDATE() for the default value.
Add the column with a default value in one statement like this answer.
ALTER TABLE dbo.registration_demo
ADD time_registered DATETIME DEFAULT GETUTCDATE();
Let's get another registrant and see what the data looks like.
INSERT INTO dbo.registration_demo (name) VALUES
('Julia');
SELECT * FROM dbo.registration_demo;
id name time_registered
1 John NULL
2 Jane NULL
3 Jeff NULL
4 Julia 2016-06-21 14:32:57.767
To make it simpler to follow, I will summarize the above answers:
Let`s say the table is called Customer
it has 4 columns/less or more...
you want to add a new column to the table where every time when there is insert... then that column keeps a record of the time the event happened.
Solution:
add a new column, let`s say timepurchase is the new column, to the table with data type datetime.
Then run the following alter:
ALTER TABLE Customer ADD CONSTRAINT DF_Customer DEFAULT GETDATE() FOR timePurchase
In SQLPlus while creating a table it is be like as
SQL> create table Test
( Test_ID number not null,
Test_Date date default sysdate not null );
SQL> insert into Test(id) values (1);
Test_ID Test_Date
1 08-MAR-19
I want to have a unique constraint on a column which I am going to populate with GUIDs. However, my data contains null values for this columns. How do I create the constraint that allows multiple null values?
Here's an example scenario. Consider this schema:
CREATE TABLE People (
Id INT CONSTRAINT PK_MyTable PRIMARY KEY IDENTITY,
Name NVARCHAR(250) NOT NULL,
LibraryCardId UNIQUEIDENTIFIER NULL,
CONSTRAINT UQ_People_LibraryCardId UNIQUE (LibraryCardId)
)
Then see this code for what I'm trying to achieve:
-- This works fine:
INSERT INTO People (Name, LibraryCardId)
VALUES ('John Doe', 'AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA');
-- This also works fine, obviously:
INSERT INTO People (Name, LibraryCardId)
VALUES ('Marie Doe', 'BBBBBBBB-BBBB-BBBB-BBBB-BBBBBBBBBBBB');
-- This would *correctly* fail:
--INSERT INTO People (Name, LibraryCardId)
--VALUES ('John Doe the Second', 'AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA');
-- This works fine this one first time:
INSERT INTO People (Name, LibraryCardId)
VALUES ('Richard Roe', NULL);
-- THE PROBLEM: This fails even though I'd like to be able to do this:
INSERT INTO People (Name, LibraryCardId)
VALUES ('Marcus Roe', NULL);
The final statement fails with a message:
Violation of UNIQUE KEY constraint 'UQ_People_LibraryCardId'. Cannot insert duplicate key in object 'dbo.People'.
How can I change my schema and/or uniqueness constraint so that it allows multiple NULL values, while still checking for uniqueness on actual data?
What you're looking for is indeed part of the ANSI standards SQL:92, SQL:1999 and SQL:2003, ie a UNIQUE constraint must disallow duplicate non-NULL values but accept multiple NULL values.
In the Microsoft world of SQL Server however, a single NULL is allowed but multiple NULLs are not...
In SQL Server 2008, you can define a unique filtered index based on a predicate that excludes NULLs:
CREATE UNIQUE NONCLUSTERED INDEX idx_yourcolumn_notnull
ON YourTable(yourcolumn)
WHERE yourcolumn IS NOT NULL;
In earlier versions, you can resort to VIEWS with a NOT NULL predicate to enforce the constraint.
SQL Server 2008 +
You can create a unique index that accept multiple NULLs with a WHERE clause. See the answer below.
Prior to SQL Server 2008
You cannot create a UNIQUE constraint and allow NULLs. You need set a default value of NEWID().
Update the existing values to NEWID() where NULL before creating the UNIQUE constraint.
SQL Server 2008 And Up
Just filter a unique index:
CREATE UNIQUE NONCLUSTERED INDEX UQ_Party_SamAccountName
ON dbo.Party(SamAccountName)
WHERE SamAccountName IS NOT NULL;
In Lower Versions, A Materialized View Is Still Not Required
For SQL Server 2005 and earlier, you can do it without a view. I just added a unique constraint like you're asking for to one of my tables. Given that I want uniqueness in column SamAccountName, but I want to allow multiple NULLs, I used a materialized column rather than a materialized view:
ALTER TABLE dbo.Party ADD SamAccountNameUnique
AS (Coalesce(SamAccountName, Convert(varchar(11), PartyID)))
ALTER TABLE dbo.Party ADD CONSTRAINT UQ_Party_SamAccountName
UNIQUE (SamAccountNameUnique)
You simply have to put something in the computed column that will be guaranteed unique across the whole table when the actual desired unique column is NULL. In this case, PartyID is an identity column and being numeric will never match any SamAccountName, so it worked for me. You can try your own method—be sure you understand the domain of your data so that there is no possibility of intersection with real data. That could be as simple as prepending a differentiator character like this:
Coalesce('n' + SamAccountName, 'p' + Convert(varchar(11), PartyID))
Even if PartyID became non-numeric someday and could coincide with a SamAccountName, now it won't matter.
Note that the presence of an index including the computed column implicitly causes each expression result to be saved to disk with the other data in the table, which DOES take additional disk space.
Note that if you don't want an index, you can still save CPU by making the expression be precalculated to disk by adding the keyword PERSISTED to the end of the column expression definition.
In SQL Server 2008 and up, definitely use the filtered solution instead if you possibly can!
Controversy
Please note that some database professionals will see this as a case of "surrogate NULLs", which definitely have problems (mostly due to issues around trying to determine when something is a real value or a surrogate value for missing data; there can also be issues with the number of non-NULL surrogate values multiplying like crazy).
However, I believe this case is different. The computed column I'm adding will never be used to determine anything. It has no meaning of itself, and encodes no information that isn't already found separately in other, properly defined columns. It should never be selected or used.
So, my story is that this is not a surrogate NULL, and I'm sticking to it! Since we don't actually want the non-NULL value for any purpose other than to trick the UNIQUE index to ignore NULLs, our use case has none of the problems that arise with normal surrogate NULL creation.
All that said, I have no problem with using an indexed view instead—but it brings some issues with it such as the requirement of using SCHEMABINDING. Have fun adding a new column to your base table (you'll at minimum have to drop the index, and then drop the view or alter the view to not be schema bound). See the full (long) list of requirements for creating an indexed view in SQL Server (2005) (also later versions), (2000).
Update
If your column is numeric, there may be the challenge of ensuring that the unique constraint using Coalesce does not result in collisions. In that case, there are some options. One might be to use a negative number, to put the "surrogate NULLs" only in the negative range, and the "real values" only in the positive range. Alternately, the following pattern could be used. In table Issue (where IssueID is the PRIMARY KEY), there may or may not be a TicketID, but if there is one, it must be unique.
ALTER TABLE dbo.Issue ADD TicketUnique
AS (CASE WHEN TicketID IS NULL THEN IssueID END);
ALTER TABLE dbo.Issue ADD CONSTRAINT UQ_Issue_Ticket_AllowNull
UNIQUE (TicketID, TicketUnique);
If IssueID 1 has ticket 123, the UNIQUE constraint will be on values (123, NULL). If IssueID 2 has no ticket, it will be on (NULL, 2). Some thought will show that this constraint cannot be duplicated for any row in the table, and still allows multiple NULLs.
For people who are using Microsoft SQL Server Manager and want to create a Unique but Nullable index you can create your unique index as you normally would then in your Index Properties for your new index, select "Filter" from the left hand panel, then enter your filter (which is your where clause). It should read something like this:
([YourColumnName] IS NOT NULL)
This works with MSSQL 2012
When I applied the unique index below:
CREATE UNIQUE NONCLUSTERED INDEX idx_badgeid_notnull
ON employee(badgeid)
WHERE badgeid IS NOT NULL;
every non null update and insert failed with the error below:
UPDATE failed because the following SET options have incorrect settings: 'ARITHABORT'.
I found this on MSDN
SET ARITHABORT must be ON when you are creating or changing indexes on computed columns or indexed views. If SET ARITHABORT is OFF, CREATE, UPDATE, INSERT, and DELETE statements on tables with indexes on computed columns or indexed views will fail.
So to get this to work correctly I did this
Right click [Database]-->Properties-->Options-->Other
Options-->Misscellaneous-->Arithmetic Abort Enabled -->true
I believe it is possible to set this option in code using
ALTER DATABASE "DBNAME" SET ARITHABORT ON
but i have not tested this
It can be done in the designer as well
Right click on the Index > Properties to get this window
Create a view that selects only non-NULL columns and create the UNIQUE INDEX on the view:
CREATE VIEW myview
AS
SELECT *
FROM mytable
WHERE mycolumn IS NOT NULL
CREATE UNIQUE INDEX ux_myview_mycolumn ON myview (mycolumn)
Note that you'll need to perform INSERT's and UPDATE's on the view instead of table.
You may do it with an INSTEAD OF trigger:
CREATE TRIGGER trg_mytable_insert ON mytable
INSTEAD OF INSERT
AS
BEGIN
INSERT
INTO myview
SELECT *
FROM inserted
END
It is possible to create a unique constraint on a Clustered Indexed View
You can create the View like this:
CREATE VIEW dbo.VIEW_OfYourTable WITH SCHEMABINDING AS
SELECT YourUniqueColumnWithNullValues FROM dbo.YourTable
WHERE YourUniqueColumnWithNullValues IS NOT NULL;
and the unique constraint like this:
CREATE UNIQUE CLUSTERED INDEX UIX_VIEW_OFYOURTABLE
ON dbo.VIEW_OfYourTable(YourUniqueColumnWithNullValues)
In my experience - if you're thinking a column needs to allow NULLs but also needs to be UNIQUE for values where they exist, you may be modelling the data incorrectly. This often suggests you're creating a separate sub-entity within the same table as a different entity. It probably makes more sense to have this entity in a second table.
In the provided example, I would put LibraryCardId in a separate LibraryCards table with a unique not-null foreign key to the People table:
CREATE TABLE People (
Id INT CONSTRAINT PK_MyTable PRIMARY KEY IDENTITY,
Name NVARCHAR(250) NOT NULL,
)
CREATE TABLE LibraryCards (
LibraryCardId UNIQUEIDENTIFIER CONSTRAINT PK_LibraryCards PRIMARY KEY,
PersonId INT NOT NULL
CONSTRAINT UQ_LibraryCardId_PersonId UNIQUE (PersonId),
FOREIGN KEY (PersonId) REFERENCES People(id)
)
This way you don't need to bother with a column being both unique and nullable. If a person doesn't have a library card, they just won't have a record in the library cards table. Also, if there are additional attributes about the library card (perhaps Expiration Date or something), you now have a logical place to put those fields.
Maybe consider an "INSTEAD OF" trigger and do the check yourself? With a non-clustered (non-unique) index on the column to enable the lookup.
As stated before, SQL Server doesn't implement the ANSI standard when it comes to UNIQUE CONSTRAINT. There is a ticket on Microsoft Connect for this since 2007. As suggested there and here the best options as of today are to use a filtered index as stated in another answer or a computed column, e.g.:
CREATE TABLE [Orders] (
[OrderId] INT IDENTITY(1,1) NOT NULL,
[TrackingId] varchar(11) NULL,
...
[ComputedUniqueTrackingId] AS (
CASE WHEN [TrackingId] IS NULL
THEN '#' + cast([OrderId] as varchar(12))
ELSE [TrackingId_Unique] END
),
CONSTRAINT [UQ_TrackingId] UNIQUE ([ComputedUniqueTrackingId])
)
You can create an INSTEAD OF trigger to check for specific conditions and error if they are met. Creating an index can be costly on larger tables.
Here's an example:
CREATE TRIGGER PONY.trg_pony_unique_name ON PONY.tbl_pony
INSTEAD OF INSERT, UPDATE
AS
BEGIN
IF EXISTS(
SELECT TOP (1) 1
FROM inserted i
GROUP BY i.pony_name
HAVING COUNT(1) > 1
)
OR EXISTS(
SELECT TOP (1) 1
FROM PONY.tbl_pony t
INNER JOIN inserted i
ON i.pony_name = t.pony_name
)
THROW 911911, 'A pony must have a name as unique as s/he is. --PAS', 16;
ELSE
INSERT INTO PONY.tbl_pony (pony_name, stable_id, pet_human_id)
SELECT pony_name, stable_id, pet_human_id
FROM inserted
END
You can't do this with a UNIQUE constraint, but you can do this in a trigger.
CREATE TRIGGER [dbo].[OnInsertMyTableTrigger]
ON [dbo].[MyTable]
INSTEAD OF INSERT
AS
BEGIN
SET NOCOUNT ON;
DECLARE #Column1 INT;
DECLARE #Column2 INT; -- allow nulls on this column
SELECT #Column1=Column1, #Column2=Column2 FROM inserted;
-- Check if an existing record already exists, if not allow the insert.
IF NOT EXISTS(SELECT * FROM dbo.MyTable WHERE Column1=#Column1 AND Column2=#Column2 #Column2 IS NOT NULL)
BEGIN
INSERT INTO dbo.MyTable (Column1, Column2)
SELECT #Column2, #Column2;
END
ELSE
BEGIN
RAISERROR('The unique constraint applies on Column1 %d, AND Column2 %d, unless Column2 is NULL.', 16, 1, #Column1, #Column2);
ROLLBACK TRANSACTION;
END
END
CREATE UNIQUE NONCLUSTERED INDEX [UIX_COLUMN_NAME]
ON [dbo].[Employee]([Username] ASC) WHERE ([Username] IS NOT NULL)
WITH (ALLOW_PAGE_LOCKS = ON, ALLOW_ROW_LOCKS = ON, PAD_INDEX = OFF, SORT_IN_TEMPDB = OFF,
DROP_EXISTING = OFF, IGNORE_DUP_KEY = OFF, STATISTICS_NORECOMPUTE = OFF, ONLINE = OFF,
MAXDOP = 0) ON [PRIMARY];
this code if u make a register form with textBox and use insert and ur textBox is empty and u click on submit button .
CREATE UNIQUE NONCLUSTERED INDEX [IX_tableName_Column]
ON [dbo].[tableName]([columnName] ASC) WHERE [columnName] !=`''`;