I have the following table:
CREATE TABLE [T_Manufacture](
[ManufactureID] [int] IDENTITY(-2147483648,1) NOT NULL,
[Manufacture] [varchar](25) NULL,
[ManufactureDescription] [varchar](50) NULL)
As we can see that the ManufactureID is identity column which is start from -2147483648. So if the identity reach -1 then the next record shoud be 0 (zero). Is it possible to skip this record? I mean, I don't wanna have an ID with value zero.
Please help.
Thank you.
This is an elaboration on Deepak's comment.
Why would anyone use negative numbers for an id column? And, if you are concerned about having 2 billion values, then you should be concerned about 4 billion and use a bigint:
CREATE TABLE T_Manufacture (
ManufactureID bigint IDENTITY(1, 1) PRIMARY KEY, -- might as well declare it
Manufacture varchar(25),
ManufactureDescription varchar(50)
);
This is the simplest way to solve your problem and to ensure that the table can grow as large as you want.
In other words, the right way to "skip" an particular value is to start the identity enumeration after that value. Or, if you really wanted:
CREATE TABLE T_Manufacture (
ManufactureID int IDENTITY(-1, -1) PRIMARY KEY, -- might as well declare it
Manufacture varchar(25),
ManufactureDescription varchar(50)
);
But once again, negative ids seem absurd.
You can control this with a trigger...
CREATE TRIGGER SkipZeroManufacture ON T_Manufacture AFTER INSERT
AS
BEGIN
IF EXISTS (SELECT 'zero record inserted' FROM inserted AS I WHERE I.ManufactureID = 0)
BEGIN
INSERT INTO T_Manufacture (
Manufacture,
ManufactureDescription)
SELECT
I.Manufacture,
I.ManufactureDescription
FROM
inserted AS I
WHERE
i.ManufactureID = 0
DELETE T_Manufacture WHERE ManufactureID = 0
END
END
Although this is an awful idea since it will be triggered on each insert, only check for one value and will need maintenance for new or updated columns. It will also switch the 0 ID'd record with another ID.
Related
I'm doing a school project about a school theme where I need to create some tables for Students, Classes, Programmes...
I want to add a Group to determined classes with an auto increment in group_id however I wanted the group_id variable to reset if I change any of those attributes(Classes_id,courses_acronym,year_Semesters) how can I reset it every time any of those change??
Here is my table:
CREATE TABLE Classes_Groups(
Classes_id varchar(2),
Group_id INT IDENTITY(1,1),
courses_acronym varchar(4),
year_Semesters varchar(5),
FOREIGN KEY (Classes_id, year_Semesters,courses_acronym) REFERENCES Classes(id,year_Semesters, courses_acronym),
PRIMARY KEY(Classes_id,courses_acronym,year_Semesters,Group_id)
);
Normally, you do not (need to) reset the identity column of a table. An identity column is used to create unique values for every single record in a table.
So you want to generate entries in your groups table based on new entries in your classes table. You might create a trigger on your classes table for that purpose.
Since Group_id is already unique by itself (because of its IDENTITY), you do not need other fields in the primary key at all. Instead, you may create a separate UNIQUE constraint for the combination (Classes_id, courses_acronym, year_Semesters) if you need it.
And if the id field of your classes table is an IDENTITY column too, you could define a primary key in your classes table solely on that id field. And then your foreign key constraint in your new groups table can only include that Classes_id field.)
So much for now. I guess that your database design needs some more additional tuning and tweaking. ;)
where are you setting the values from?, you can have a stored proc and in your query have the columns have an initial value set when stored proc is hit assuming there are values at the beginning
.Then use an IF statement.
declare #initial_Classes_id varchar(2) = --initial value inserted
declare #initial_courses_acronym varchar(4) = --initial value inserted
declare #initial_year_Semesters varchar(5) = --initial value inserted
declare #compare_Classes_id varchar(2) = (select top 1 Classes_id from Classes_Groups order by --PK column desc for last insert); l would add Dateadded and then order with last insert date
declare #compare_courses_acronym varchar(2) = (select top 1 Classes_id from Classes_Groups where Classes_id = #compare_Classes_id);
declare #compare_year_Semesters varchar(2) = (select top 1 Classes_id from Classes_Groups where Classes_id = #compare_Classes_id);
IF (#initial_Classes_id != #compare_Classes_id OR #initial_courses_acronym != #compare_courses_acronym OR #initial_year_Semesters != #compare_year_Semesters)
BEGIN
DBCC CHECKIDENT ('Group_id', RESEED, 1)
Insert into Classes_Groups (courses_acronym,year_Semesters)
values (
courses_acronym,
year_Semesters
)
END
ELSE
BEGIN
Insert into Classes_Groups (courses_acronym,year_Semesters)
values (
courses_acronym,
year_Semesters
)
END
NB: would advice to use int on the primary key. Unless you have a specific purpose of doing so.
How can I enforce a table to have only one row? Below is what I tried. The UPDATE trigger might work, however, the CREATE trigger definitely will not. For the CREATE, I would like to use SET, however, SET is not supported by SQLite.
CREATE TABLE IF NOT EXISTS `config` (
`id` TINYINT NOT NULL DEFAULT 0,
`subdomain` VARCHAR(45) NOT NULL,
`timezone` CHAR(3) NOT NULL,
`timeout` TINYINT NOT NULL,
`offline` TINYINT NOT NULL,
`hash_config` CHAR(32) NOT NULL,
`hash_points` CHAR(32) NOT NULL,
PRIMARY KEY (`id`));
INSERT INTO config(id,subdomain,timezone,timeout,offline,hash_config,hash_points) VALUES(0,'subdomain','UTC',5,0,'hash_config','hash_points');
CREATE TRIGGER `config_insert_zero`
BEFORE INSERT ON `config`
FOR EACH ROW
BEGIN
-- SET NEW.id=0;
NEW.id=OLD.id;
END;
CREATE TRIGGER `config_update_zero`
BEFORE UPDATE ON `config`
FOR EACH ROW
BEGIN
-- SET NEW.id=0;
NEW.id=OLD.id;
END;
In the general case, to limit the number of rows in a table, you have to prevent any further insert.
In SQLite, this is done with RAISE():
CREATE TRIGGER config_no_insert
BEFORE INSERT ON config
WHEN (SELECT COUNT(*) FROM config) >= 1 -- limit here
BEGIN
SELECT RAISE(FAIL, 'only one row!');
END;
However, if the limit is one, you could instead simply constrain the primary key to a fixed value:
CREATE TABLE config (
id INTEGER PRIMARY KEY CHECK (id = 0),
[...]
);
One idea you may want to consider is to make it appear like the table has only one row. In reality, you keep all previous rows because it's quite possible you will one day want to maintain a history of all past values.
Since there is only one row, there really is no need for an ID column, the purpose of which is to uniquely differentiate each row from all the others. You do need, however, a timestamp which will be used to identify the "one row" which will be the latest row written to the table.
CREATE TABLE `config_history` (
`created` timestamp default current_timestamp,
`subdomain` VARCHAR(45) NOT NULL,
`timezone` CHAR(3) NOT NULL,
`timeout` TINYINT NOT NULL,
`offline` TINYINT NOT NULL,
`hash_config` CHAR(32) NOT NULL,
`hash_points` CHAR(32) NOT NULL,
PRIMARY KEY (`created`)
);
Since you are normally interested in only the last row written (the latest version), the query selects the row with the latest creation date:
select ch.created effective_date, ch.subdomain, ch.timezone, ch.timeout,
ch.offline, ch.hash_config, ch.hash_points
from config_history ch
where ch.created =(
select max( created )
from config_history );
Put a create view config as in front of this query and you have a view that selects only one row, the latest, from the table. Any query against the view returns the one row:
select *
from config;
An instead of trigger on the view can convert Updates to Inserts -- you don't actually want to change a value, just write a new row with the new values. This then becomes the new "current" row.
Now you have what appears to be a table with only one row but you also maintain a complete history of all the past changes ever made to that row.
I have a table A with an Identity Column which is the primary key.
The primary key is at the same time a foreign key that points towards another table B.
I am trying to build an insert trigger that inserts into Table B the identity column that is about to be created in table A and another custom value for example '1'.
I tried using ##Identity but I keep getting a foreign key conflict. Thanks for your help.
create TRIGGER dbo.tr ON dbo.TableA FOR INSERT
AS
SET NOCOUNT ON
begin
insert into TableB
select ##identity, 1;
end
alexolb answered the question himself in the comments above. Another alternative is to use the IDENT_CURRENT function instead of selecting from the table. The drawback of this approach is that it always starts your number one higher than the seed, but that is easily remedied by setting the seed one unit lower. I think it feels better to use a function than a subquery.
For example:
CREATE TABLE [tbl_TiggeredTable](
[id] [int] identity(0,1) NOT NULL,
[other] [varchar](max)
)
CREATE TRIGGER [trgMyTrigger]
ON [tbl_TriggeredTable]
INSTEAD OF INSERT,UPDATE,DELETE
SET identity_insert tbl_TriggeredTable ON
INSERT INTO tbl_TriggeredTable (
[id],
[other]
)
SELECT
-- The identity column will have a zero in the insert table when
-- it has not been populated yet, so we need to figure it out manually
case i.[id]
when 0 then IDENT_CURRENT('tbl_TriggeredTable') + IDENT_INCR('tbl_TriggeredTable')
ELSE i.[id]
END,
i.[other],
FROM inserted i
SET identity_insert tbl_TriggeredTable OFF
END
I have the following SQL I trigger in a C# app.
All works well but the ID table doesn't auto increment. It creates the value of 1 for the first entry then will not allow other inserts due to not being able to create a unquie ID.
Here is the SQL:
CREATE TABLE of_mapplist_raw (
id integer PRIMARY KEY NOT NULL,
form_name varchar(200) NOT NULL,
form_revi varchar(200) NOT NULL,
source_map varchar(200),
page_num varchar(200) NOT NULL,
fid varchar(200) NOT NULL,
fdesc varchar(200) NOT NULL
)";
I'm sure its a schoolboy error at play here.
you need to specify its seed and increment.( plus , i dont think there is integer keyword ....)
id [int] IDENTITY(1,1) NOT NULL,
the first value is the seed
the second one is the delta between increases
A Question you might ask :
delta between increases ? why do i need that ? its always 1 ....??
well - yes and no. sometimes you want to leave a gap between rows - so you can later insert rows between... specially if its clustered index by that key....and speed is important... so you can pre-design it to leave gaps.
p.s. ill be glad to hear other scenarios from watchers.
You need to mention the Identity.
id int IDENTITY(1,1) NOT NULL
How could I set a constraint on a table so that only one of the records has its isDefault bit field set to 1?
The constraint is not table scope, but one default per set of rows, specified by a FormID.
Use a unique filtered index
On SQL Server 2008 or higher you can simply use a unique filtered index
CREATE UNIQUE INDEX IX_TableName_FormID_isDefault
ON TableName(FormID)
WHERE isDefault = 1
Where the table is
CREATE TABLE TableName(
FormID INT NOT NULL,
isDefault BIT NOT NULL
)
For example if you try to insert many rows with the same FormID and isDefault set to 1 you will have this error:
Cannot insert duplicate key row in object 'dbo.TableName' with unique
index 'IX_TableName_FormID_isDefault'. The duplicate key value is (1).
Source: http://technet.microsoft.com/en-us/library/cc280372.aspx
Here's a modification of Damien_The_Unbeliever's solution that allows one default per FormID.
CREATE VIEW form_defaults
AS
SELECT FormID
FROM whatever
WHERE isDefault = 1
GO
CREATE UNIQUE CLUSTERED INDEX ix_form_defaults on form_defaults (FormID)
GO
But the serious relational folks will tell you this information should just be in another table.
CREATE TABLE form
FormID int NOT NULL PRIMARY KEY
DefaultWhateverID int FOREIGN KEY REFERENCES Whatever(ID)
From a normalization perspective, this would be an inefficient way of storing a single fact.
I would opt to hold this information at a higher level, by storing (in a different table) a foreign key to the identifier of the row which is considered to be the default.
CREATE TABLE [dbo].[Foo](
[Id] [int] NOT NULL,
CONSTRAINT [PK_Foo] PRIMARY KEY CLUSTERED
(
[Id] ASC
) ON [PRIMARY]
) ON [PRIMARY]
GO
CREATE TABLE [dbo].[DefaultSettings](
[DefaultFoo] [int] NULL
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[DefaultSettings] WITH CHECK ADD CONSTRAINT [FK_DefaultSettings_Foo] FOREIGN KEY([DefaultFoo])
REFERENCES [dbo].[Foo] ([Id])
GO
ALTER TABLE [dbo].[DefaultSettings] CHECK CONSTRAINT [FK_DefaultSettings_Foo]
GO
You could use an insert/update trigger.
Within the trigger after an insert or update, if the count of rows with isDefault = 1 is more than 1, then rollback the transaction.
CREATE VIEW vOnlyOneDefault
AS
SELECT 1 as Lock
FROM <underlying table>
WHERE Default = 1
GO
CREATE UNIQUE CLUSTERED INDEX IX_vOnlyOneDefault on vOnlyOneDefault (Lock)
GO
You'll need to have the right ANSI settings turned on for this.
I don't know about SQLServer.But if it supports Function-Based Indexes like in Oracle, I hope this can be translated, if not, sorry.
You can do an index like this on suposed that default value is 1234, the column is DEFAULT_COLUMN and ID_COLUMN is the primary key:
CREATE
UNIQUE
INDEX only_one_default
ON my_table
( DECODE(DEFAULT_COLUMN, 1234, -1, ID_COLUMN) )
This DDL creates an unique index indexing -1 if the value of DEFAULT_COLUMN is 1234 and ID_COLUMN in any other case. Then, if two columns have DEFAULT_COLUMN value, it raises an exception.
The question implies to me that you have a primary table that has some child records and one of those child records will be the default record. Using address and a separate default table here is an example of how to make that happen using third normal form. Of course I don't know if it's valuable to answer something that is so old but it struck my fancy.
--drop table dev.defaultAddress;
--drop table dev.addresses;
--drop table dev.people;
CREATE TABLE [dev].[people](
[Id] [int] identity primary key,
name char(20)
)
GO
CREATE TABLE [dev].[Addresses](
id int identity primary key,
peopleId int foreign key references dev.people(id),
address varchar(100)
) ON [PRIMARY]
GO
CREATE TABLE [dev].[defaultAddress](
id int identity primary key,
peopleId int foreign key references dev.people(id),
addressesId int foreign key references dev.addresses(id))
go
create unique index defaultAddress on dev.defaultAddress (peopleId)
go
create unique index idx_addr_id_person on dev.addresses(peopleid,id);
go
ALTER TABLE dev.defaultAddress
ADD CONSTRAINT FK_Def_People_Address
FOREIGN KEY(peopleID, addressesID)
REFERENCES dev.Addresses(peopleId, id)
go
insert into dev.people (name)
select 'Bill' union
select 'John' union
select 'Harry'
insert into dev.Addresses (peopleid, address)
select 1, '123 someplace' union
select 1,'work place' union
select 2,'home address' union
select 3,'some address'
insert into dev.defaultaddress (peopleId, addressesid)
select 1,1 union
select 2,3
-- so two home addresses are default now
-- try adding another default address to Bill and you get an error
select * from dev.people
join dev.addresses on people.id = addresses.peopleid
left join dev.defaultAddress on defaultAddress.peopleid = people.id and defaultaddress.addressesid = addresses.id
insert into dev.defaultaddress (peopleId, addressesId)
select 1,2
GO
You could do it through an instead of trigger, or if you want it as a constraint create a constraint that references a function that checks for a row that has the default set to 1
EDIT oops, needs to be <=
Create table mytable(id1 int, defaultX bit not null default(0))
go
create Function dbo.fx_DefaultExists()
returns int as
Begin
Declare #Ret int
Set #ret = 0
Select #ret = count(1) from mytable
Where defaultX = 1
Return #ret
End
GO
Alter table mytable add
CONSTRAINT [CHK_DEFAULT_SET] CHECK
(([dbo].fx_DefaultExists()<=(1)))
GO
Insert into mytable (id1, defaultX) values (1,1)
Insert into mytable (id1, defaultX) values (2,1)
This is a fairly complex process that cannot be handled through a simple constraint.
We do this through a trigger. However before you write the trigger you need to be able to answer several things:
do we want to fail the insert if a default exists, change it to 0 instead of 1 or change the existing default to 0 and leave this one as 1?
what do we want to do if the default record is deleted and other non default records are still there? Do we make one the default, if so how do we determine which one?
You will also need to be very, very careful to make the trigger handle multiple row processing. For instance a client might decide that all of the records of a particular type should be the default. You wouldn't change a million records one at a time, so this trigger needs to be able to handle that. It also needs to handle that without looping or the use of a cursor (you really don't want the type of transaction discussed above to take hours locking up the table the whole time).
You also need a very extensive tesing scenario for this trigger before it goes live. You need to test:
adding a record with no default and it is the first record for that customer
adding a record with a default and it is the first record for that customer
adding a record with no default and it is the not the first record for that customer
adding a record with a default and it is the not the first record for that customer
Updating a record to have the default when no other record has it (assuming you don't require one record to always be set as the deafault)
Updating a record to remove the default
Deleting the record with the deafult
Deleting a record without the default
Performing a mass insert with multiple situations in the data including two records which both have isdefault set to 1 and all of the situations tested when running individual record inserts
Performing a mass update with multiple situations in the data including two records which both have isdefault set to 1 and all of the situations tested when running individual record updates
Performing a mass delete with multiple situations in the data including two records which both have isdefault set to 1 and all of the situations tested when running individual record deletes
#Andy Jones gave an answer above closest to mine, but bearing in mind the Rule of Three, I placed the logic directly in the stored proc that updates this table. This was my simple solution. If I need to update the table from elsewhere, I will move the logic to a trigger. The one default rule applies to each set of records specified by a FormID and a ConfigID:
ALTER proc [dbo].[cpForm_UpdateLinkedReport]
#reportLinkId int,
#defaultYN bit,
#linkName nvarchar(150)
as
if #defaultYN = 1
begin
declare #formId int, #configId int
select #formId = FormID, #configId = ConfigID from csReportLink where ReportLinkID = #reportLinkId
update csReportLink set DefaultYN = 0 where isnull(ConfigID, #configId) = #configId and FormID = #formId
end
update
csReportLink
set
DefaultYN = #defaultYN,
LinkName = #linkName
where
ReportLinkID = #reportLinkId