I have a table, in which I have a column to store user name. I was stroring it as varchar of format user1,user2,user3(its not inserted by user,automatically it should get generated) So for this I need to get the max int value of users and then increment it by 1 and append it with string user and store it to the next row.
If you insist on saving the user prefix to the number, you can add an identity column, and create that user column as a computed column:
CREATE TABLE tblUsers
(
UserId int Identity(1,1) PRIMARY KEY,
UserName As 'User'+ CAST(UserId as varchar),
-- Other columns
)
This way whenever you select the UserName column it's value will be calculated.
You can also specify it as PERSISTED, meaning it's value will be saved in the database and only change if the value of one of it's components will change.
The big benefit here is that the database will handle all the hard work for you, plus uniqueness is guaranteed since it's based on the value of the primary key of the table.
Add an auto-incremented field,
CREATE TABLE Users
(
ID int NOT NULL AUTO_INCREMENT=1,
LastName varchar(255) ... ,
FirstName varchar(255) ... ,
... ,
SeqToken varchar(255)
)
Than create a trigger on insert:
The trigger will auto-generate the SeqToken field:
CREATE TRIGGER trig_insert_user
ON [Users]
AFTER INSERT
AS
UPDATE [Users]
SET SeqToken='User'+CAST(ID AS VARCHAR)
WHERE ID=INSERTED.ID
Related
This is my first question on this platform. I am working on a database project. I want to use autoincrement for my primary key for id, but also want to add an alphabet before it. Are there other ways to do it apart from using 2 columns declaring one as identity and casting the other? I have worked with stored procedures and triggers.
Thank you
PS: I want to do it using one column if possible
You won't be able to do this with just one column.
The best solution is to use
an ID INT IDENTITY(1,1) column to get SQL Server to handle the automatic increment of your numeric value
a computed, persisted column to convert that numeric value to the value you need
So try this:
CREATE TABLE dbo.tblCompany
(
ID INT IDENTITY(1,1) NOT NULL PRIMARY KEY CLUSTERED,
CompanyID AS 'CMP-' + RIGHT('00000' + CAST(ID AS VARCHAR(5)), 5) PERSISTED,
.... your other columns here....
)
Now, every time you insert a row into tblCompany without specifying values for ID or CompanyID:
INSERT INTO dbo.tblCompany(Col1, Col2, ..., ColN)
VALUES (Val1, Val2, ....., ValN)
then SQL Server will increase your ID value, and CompanyID will contain values like CMP-00001, CMP-00002,...... and so on - automatically. The CompanyID column will be fill automatically, by SQL Server, upon inserting a new row - so there's no need for triggers or stored procedures or anything else - just this declaration in your table definition.
UPDATE: if you're using SQL Server 2012 or newer, you can do it with just one column - if you also create a SEQUENCE - like this:
CREATE SEQUENCE SEQ_CompanyID
AS INT
START WITH 1000
INCREMENT BY 1;
CREATE TABLE dbo.Company
(
CompanyID VARCHAR(20) NOT NULL
CONSTRAINT DF_CompanyID
DEFAULT('CMP-' + CAST(NEXT VALUE FOR dbo.SEQ_CompanyID AS VARCHAR(10))),
CompanyName VARCHAR(100) NOT NULL,
----- other columns here
)
Now if you make sure to insert with omitting the CompanyID column in the insert statement, like this:
INSERT INTO dbo.Company (CompanyName)
VALUES ('Company #1'), ('Company ABC'), ('Company Three');
then you get CMP-1001', 'CMP-1002 etc. as your CompanyID, again, automatically handled by SQL Server upon inserting a new row.
In SQL Server, I have created a Table with an ID column that I have made an IDENTITY COLUMN,
EmployeeID int NOT NULL IDENTITY(100,10) PRIMARY KEY
It is my understanding, when I use the IDENTITY feature, it auto increments the EmployeeID. What I don't know/not sure is:
Is that IDENTITY number created, unique?
Does SQL search the entire column in the table to confirm the number created does not already exist?
Can I override that auto increment number manually?
If I did manually override that number, would the number I enter be checked to make sure it is not a duplicate/existing ID number?
Thanks for any help provided.
Is that IDENTITY number created, unique?
Yes, Identity property is unique
Does SQL search the entire column in the table to confirm the number created does not already exist? \
It need not, what this property does is, just incrementing the old value
Can I override that auto increment number manually?
Yes, you can. You have to use SET IDENTITY_INSERT TABLENAME ON
If I did manually override that number, would the number I enter be checked to make sure it is not a duplicate/existing ID number?
No, that won't be taken care by SQL Server, you will have to ensure you have constraints to take care of this
Below is a simple demo to prove that
create table #temp
(
id int identity(1,1)
)
insert into #temp
default values
go 3
select * from #temp--now id column has 3
set identity_insert #temp on
insert into #temp (id)
values(4)
set identity_insert #temp off
select * from #temp--now id column has 4
insert into #temp
default values
go
select * from #temp--now id column has 5,next value from the last highest
Updating info from comments:
Identity column will allow gaps once you reseed them,also you can't update them
CREATE TABLE Persons
(
P_Id varchar(6) NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
PRIMARY KEY (P_Id)
)
in this table P_Id is the primary key. We want to generate autoincrement of P_Id with default value (PN00) in the start while inserting only LastName and FirstName .eg :-PN001 for first entry ,PN002 for second,PN003 for third and so on .
The only viable solution is to use
an ID INT IDENTITY(1,1) column to get SQL Server to handle the automatic increment of your numeric value
a computed, persisted column to convert that numeric value to the value you need
So try this:
CREATE TABLE dbo.Persons
(ID INT IDENTITY(1,1) NOT NULL PRIMARY KEY CLUSTERED,
P_ID AS 'PN' + RIGHT('00000' + CAST(ID AS VARCHAR(5)), 5) PERSISTED,
.... your other columns here....
)
Now, every time you insert a row into Persons without specifying values for ID or P_ID:
INSERT INTO dbo.Persons(Col1, Col2, ..., ColN)
VALUES (Val1, Val2, ....., ValN)
then SQL Server will automatically and safely increase your ID value, and P_Id will contain values like PN00001, PN00002,...... and so on - automatically, safely, reliably, no duplicates.
There are different ways to address your issue.
You could use a Trigger.Triggers are activated on some events. You could create a trigger for 'Instead of Insert On Persons' event. When the event is triggered, then generate a new P_Id. Insert this new P_Id alongwith all the values as the new record for your table.
This approach wont have coupling with the table's schema.
Refer this link for more information on Triggers :
https://msdn.microsoft.com/en-IN/library/ms189799.aspx
Refer this link to emulate 'before insert trigger' in SQL Server:
How to emulate a BEFORE INSERT trigger in T-SQL / SQL Server for super/subtype (Inheritence) entities?
You could also use a Procedure like :
create procedure Persons_insert(#lastname varchar(255), #firstname varchar(255))
as
begin
--write code to generate the ID as you like
insert into Persons(p_id,lastname,firstname)values(generated_id,lastname,firstname);
end
Within the context of SQLite.
I have an existing table which is currently populated with numerous rows of data.
I am trying to add a new primary key column to this table whilst persisting the original data.
As demonstrated below, I have tried the following
Add a new column to the existing table (Id INTEGER).
Change the name of the existing table.
Create a new table which includes the new primary key (Id INTEGER PRIMARY KEY).
Insert all data from the renamed table into the newly created table.
Drop the renamed table.
The reason I thought this would work is because according to SQlite documentation,
A column declared INTEGER PRIMARY KEY will autoincrement.
However I am receiving the following error.
ErrorCode : 19
Message : constraint failed
UNIQUE constraint failed: Person.Id
Result : Constraint
Here is my code.
--Add a new column to the existing table(Id INT).
ALTER TABLE [Person]
ADD Id INTEGER;
--Change the name of the existing table.
ALTER TABLE [Person] RENAME TO Person_temp;
--Create a new table which includes the new PK.
CREATE TABLE Person(
Id INTEGER PRIMARY KEY,
FirstName nvarchar(100) NULL,
LastName nvarchar(100) NULL
);
--Insert all data from the renamed table into the new table.
INSERT INTO Person SELECT * FROM Person_temp;
--Drop the renamed table.
DROP TABLE Person_temp;
Could anyone be kind enough to shed some light?
Since you do not declare column names in your insert query, the column order depends on the order in witch they where created / added. Try to specify the column names. This is usually a good practice anyway
--Insert all data from the renamed table into the new table.
INSERT INTO Person(Id, FirstName, LastName) SELECT Id, FirstName, LastName FROM Person_temp;
By the way, you probably don't need to add the Id column in the first table :
--Insert all data from the renamed table into the new table.
INSERT INTO Person(FirstName, LastName) SELECT FirstName, LastName FROM Person_temp;
the implicit null value for Id will be replaced by the autoincrement
It sure seems like your Id column does not contain unique value in each row. Since you just added the column, each row will have the same value.
The auto increment is there to help when you insert new rows. (You don't have to select max(id), and insert the new row with id = max+1). It won't auto-populate an existing table of data.
SQLite already has a column that could work for what you want. It's called ROWID. Try using that instead of duplicating it with your Id column.
I have the below table.
create table mytable(
physical_id int auto_increment,
logical_id int,
data varchar(20),
version_start_date datetime,
version_end_date datetime,
primary key(physical_id),
unique key(logical_id,version_start_date, version_end_date)
);
The idea behind the schema is, I want to keep track of modification to
every row and find the valid row on any particular date by checking the
version_start_date and version_end_date. I want my logical id to be
auto_increment, but mysql allows only one id to be auto_increment.
So, I want to set logical_id to physical_id, when creating a new row. I
am able to do it using the trigger.
delimiter $$
create trigger myTrigger before insert on mytable for each row begin set
new.logical_id = (select auto_increment from information_schema.tables
where table_schema = database() and table_name = 'mytable') ; end$$
delimiter ;
Few other options I checked out are, http://feedblog.org/2007/06/20/portable-sequence-generation-with-mysql/ and http://www.redhat.com/docs/en-US/JBoss_Hibernate/3.2.4.sp01.cp03/html/Reference_Guide/Native_SQL-Custom_SQL_for_create_update_and_delete.html
The problem with these approaches is, I have to create a new sequence table and keep inserting a record into that table.
Is there a better alternative?
Thank you
Bala
-- Update
I am not sure why #tpdi, why I need parent, when I can just emulate this with below table.
create table logical_id_seq (
logical_id int auto_increment,
primary key(logical_id)
);
create table mytable (
physical_id int auto_increment,
logical_id int not null references parent(logical_id),
data varchar(20),
version_start_date datetime not null,
version_end_date datetime not null,
primary key(physical_id),
foreign key (logical_id) references logical_id_seq(logical_id),
unique key (logical_id,version_start_date,version_end_date)
);
This is why I prefer Oracle/PostgreSQL sequences to MySQL's auto_increment and SQL Server's IDENTITY - you'd be able to define multiple sequences for this.
Creating a separate table solely for a column in order to use auto_increment for an additional auto_increment is the best solution I can think of, accessed via trigger or stored procedure.
Why wouldn't you want to have a table with the current version, and then an additional table for a history? Then, you use an insert into the current version table to generate your ID, and only query the history table when you actually need the history information.
Now I understand your issue :). Changing my answer.
You will need to use some trigger so that whenever some row is edited logical id is incremented by 1 finding max of logical id available in table.
create table parent (
logical_id int auto_increment,
physical_id int null references mytable(id)
);
create table mytable(
physical_id int auto_increment,
logical_id not null references parent(logical_id),
data varchar(20),
version_start_date datetime,
version_end_date datetime,
primary key(physical_id)
);
To insert a new instance of an existing record, insert into mytable ...., then capture new mytable.id, and update parent's physical_id with it (possibly in a trigger).
Now, to look up the current record, look up the logical id in parent, and use parent.physical_id to join to the correct record in "mytable"
Parent points to the current valid record (of all records) in "mytable".
To find all instances of a logical record, use the logical_id in "mytable".
To insert a wholly new record, first insert into parent to get the new logical_id, then insert the data in "mytable"; this is why we allow parent.physical_id to be nullable.
As to the OP's update: yes, you can "emulate" by just "stealing" a sequence, but that doesn't model what's really going on. "Stealing" the sequence is just an implementation detail; having two tables as I've shown above makes explicit what's really going on, namely: I have a current state (which parent points to) in "mytable", and 0, 1 or many prior states in "mytable". It's a cleaner separation of concerns, a table that tells you "what's current for any id", and a table that tells you "the data of that current state, and the data of prior states".