I would like to create table with CHECK constraint, where CHECK calls an user defined scalar function. I have read on multiple sites that it is possible, also that it has bad performance. Even though I would like to do it.
I have this table
CREATE TABLE [book_history] (
id int NOT NULL IDENTITY PRIMARY KEY,
user_id int NOT NULL,
library_id int NOT NULL,
book_id int NOT NULL,
borrow_time datetime DEFAULT GETDATE(),
return_policy datetime DEFAULT DATEADD(DAY, 30, GETDATE()),
return_time datetime,
CHECK (dbo.fn_check_duplicate(user_id, library_id, book_id) = 0)
);
and function
DROP FUNCTION IF EXISTS fn_check_duplicate
GO
CREATE FUNCTION fn_check_duplicate (#user_id int, #library_id int, #book_id int)
RETURNS int
BEGIN
RETURN (SELECT COUNT(*) FROM [book_history] WHERE user_id = #user_id AND library_id = #library_id AND book_id = #book_id AND return_time IS NULL)
END
GO
When I try to insert new row into this book_history table (which is empty), I get an error saying The INSERT statement conflicted with the CHECK constraint "CK__book_history__267ABA7A". The conflict occurred in database "library", table "dbo.book_history".
COUNT is supposed to return int data type based on MSDN documentation.
I am owner of both, the table and the function.
Can anyone tell me what am I doing wrong?
Change it to check (dbo.fn_check_duplicate(user_id, library_id, book_id) = 1)
The check is going to look at the state of the table after the insert, so you want the count to be 1.
Test it on rextester: http://rextester.com/AWDNP40594 by uncommenting the second insert.
You can also replace this slow check constraint with a filtered unique index like so:
create unique nonclustered index uix_book_history_user_library_book
on dbo.book_history (user_id, library_id, book_id)
where return_time is null
This might be more of what you are trying to do, if each book_id is an individual book:
create unique nonclustered index uix_book_history_library_book
on dbo.book_history (library_id, book_id)
where return_time is null
Because this would allow a book to only be checked out by one user at a time.
Related
First here's the relevant code:
create table customer(
customer_mail_address varchar(255) not null,
subscription_start date not null,
subscription_end date, check (subscription_end !< subcription start)
constraint pk_customer primary key (customer_mail_address)
)
create table watchhistory(
customer_mail_address varchar(255) not null,
watch_date date not null,
constraint pk_watchhistory primary key (movie_id, customer_mail_address, watch_date)
)
alter table watchhistory
add constraint fk_watchhistory_ref_customer foreign key (customer_mail_address)
references customer (customer_mail_address)
on update cascade
on delete no action
go
So i want to use a UDF to constrain the watch_date in watchhistory between the subscription_start and subscription_end in customer. I can't seem to figure it out.
Check constraints can't validate data against other tables, the docs say (emphasis mine):
[ CONSTRAINT constraint_name ]
{
...
CHECK [ NOT FOR REPLICATION ] ( logical_expression )
}
logical_expression
Is a logical expression used in a CHECK constraint and returns TRUE or
FALSE. logical_expression used with CHECK constraints cannot
reference another table but can reference other columns in the same
table for the same row. The expression cannot reference an alias data
type.
That being said, you can create a scalar function that validates your date, and use the scalar function on the check condition instead:
CREATE FUNCTION dbo.ufnValidateWatchDate (
#WatchDate DATE,
#CustomerMailAddress VARCHAR(255))
RETURNS BIT
AS
BEGIN
IF EXISTS (
SELECT
'supplied watch date is between subscription start and end'
FROM
customer AS C
WHERE
C.customer_mail_address = #CustomerMailAddress AND
#WatchDate BETWEEN C.subscription_start AND C.subscription_end)
BEGIN
RETURN 1
END
RETURN 0
END
Now add your check constraint so it validates that the result of the function is 1:
ALTER TABLE watchhistory
ADD CONSTRAINT CHK_watchhistory_ValidWatchDate
CHECK (dbo.ufnValidateWatchDate(watch_date, customer_mail_address) = 1)
This is not a direct link to the other table, but a workaround you can do to validate the date. Keep in mind that if you update the customer dates after the watchdate insert, dates will be inconsistent. The only way to ensure full consistency in this case would be with a few triggers.
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.
Does SQL have an OR or | equivalent for attribute types that are only one of a few possibliities (ie Enum types)?
Example using my best guess for the status attribute in the following table:
CREATE TABLE Rental (
status ("open" | "closed"),
date datetime,
id int PRIMARY KEY
)
I want status to be either "open" or "closed", nothing else. Is there syntax for this, or should I use CHAR(6) or should I use a constraint instead?
You may use check constraints when defining you table to narrow the domain of the attribute.
CREATE TABLE Rental (
status char(6),
date datetime,
id int PRIMARY KEY
);
alter table Rental
add constraint status_valid_value
check (status is null or (status in ('open','closed')));
CREATE TABLE Rental (
status char(6),
date datetime,
id int PRIMARY KEY
Check (status='open' OR status='closed')
)
It's also better to store status like int (1- open, 0 - closed, an so on)
create table Linq_TB
{
url_id int NOTNULL,
Pg_Name nvarchar(50) NOTNULL,
URL nvarchar(50) NUTNULL,
CONSTRAINT Linq_id PRIMARY KEY (url_id,DBCC Checkident(Linq_TB,RESEED,0) case url_id not in(select URL_Id from URL_TB ))
}
I want to make a table which it's primary key is Linq_id and gets it's value from both the url_id and identity with start from 1 and increments 1 by 1. url_id is a foreign key. For example if url_id is 1, linq_id's will be 11, 12, 13,... and I also want to reset linq_id identity when the url_id changes.
What should the query be? The query above doesn't work, why?
Thanks in advance
Well, a constraint contains conditions and not code to be executed. You should consider using a stored procedure for your task and also a homegrown method of assigning IDs.
However, it is not a common practice to have your primary keys 'pretty' or formatted, as there is no real benefit (except maybe for debugging purposes maybe).
I do not recommend executing DBCC whenever your url_ID changes. This has a great negative impact on performance.
Why don't you leave the IDs like they are?
You can do this with the following table and trigger definitions:
CREATE TABLE Linq_TB
(
url_id INT NOT NULL,
Linq_id INT NOT NULL,
Pg_Name NVARCHAR(50) NOT NULL,
URL NVARCHAR(50) NOT NULL,
CONSTRAINT PK_Link_TB PRIMARY KEY (url_id, Linq_id),
CONSTRAINT FK_URL_TB_URL_ID FOREIGN KEY (url_id) REFERENCES URL_TB (url_id)
)
GO
CREATE TRIGGER tr_Linq_TB_InsertUpdate
ON Linq_TB
INSTEAD OF INSERT
AS
INSERT INTO Linq_TB
SELECT i.url_id,
ISNULL(tb.Linq_id, 0)
+ row_number() over (partition by i.url_id order by (select 1)),
i.Pg_Name, i.URL
FROM inserted i
LEFT OUTER JOIN
(
SELECT url_id, MAX(Linq_ID) Linq_id
FROM Linq_TB
GROUP BY url_id
) tb ON i.url_id = tb.url_id
GO
The CREATE TABLE defines your columns and constraints. And, the trigger creates the logic to generate a sequence value in your Linq_id column for each url_id.
Note that the logic in the trigger is not complete. A couple of issues are not addressed: 1) If the url_id changes for a row, the trigger doesn't update the Link_id, and 2) deleting rows will lead to gaps in the Linq_TB column sequence.
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