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)
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.
Table Users:
ID PK INT
USER_TYPE VARCHAR(50) NOT NULL
CREATED_DATE DATETIME2(7) NOT NULL
I have this table with 50 million rows, and it is queries using the following where clause:
WHERE
u.USER_TYPE= 'manager'
AND u.CREATED_DATE >= #StartDate
AND u.CREATED_DATE < #EndDate
What would be a good starting point for an index on this table to optimize for the above query where clause?
For that query, the index you want is a composite index with two columns: (user_type, created_date). The order matters, you want user_type first because of the equality comparison.
You'll be well served by creating a table with user types having an arbitrary INT ID and referring to the manager type by ID, instead of having the manager type directly in the users table. This will narrow the table data as well as any index referring to the user type.
CREATE TABLE user_type (
id INT NOT NULL IDENTITY(1,1),
description NVARCHAR(128) NOT NULL,
CONSTRAINT pk_user_type PRIMARY KEY CLUSTERED(id)
);
CREATE TABLE users (
id INT NOT NULL IDENTITY(1,1),
user_type_id INT NOT NULL,
created_date DATETIME2(7) NOT NULL,
CONSTRAINT pk_users PRIMARY KEY CLUSTERED(id),
CONSTRAINT fk_users_user_type FOREIGN KEY(user_type_id) REFERENCES user_type(id)
);
CREATE NONCLUSTERED INDEX
ix_users_type_created
ON
users (
user_type_id,
created_date
);
You would be querying using the user_type ID rather than directly with the text of course.
For any query. Run the query in SSMS with "Include Actual Execution Plan" on. SSMS will advice an index if it feels proper index doesn't exist.
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.
I'm designing a new database for a company, trying to keep strict constraints with foreign keys etc for integrity. I have a table [Member] which holds companies on the system. This table has a column of [internalContact] for the user in our company who deals with this member which has a foreign linked to the users table by user id.
What I would like to know is if it is possible to assign a condition to the foreign key, since the users table contains internal and external users. ie. for the field to only accept a user id where the user type is 5. Can this be done, or can I only control this in my application code?
Thanks
You can use a check constraint for this.
(The code is untested some syntax errors will be in there)
CREATE TABLE Member
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
InternalContactId
CONSTRAINT chk_Person CHECK (isInternalUser(internalContactId) > 0)
)
ALTER TABLE Member
ADD FOREIGN KEY (InternalContacId)
REFERENCES Persons(P_Id)
Then just create a function isInternalUser that returns 1 if user in ok to be an internal contact
CREATE FUNCTION isInternalUser ( #userId int(10) )
RETURNS int
AS
BEGIN
DECLARE #tmp int
SELECT #tmp = count(*)
FROM users
WHERE userId = #UserId and <check to see if user is internal>
RETURN(#CtrPrice)
END
GO
Im a beginner in database and i got this difficult auction database project.
Im using SQL Server Management Studio also.
create table user(
name char(10) not null,
lastname char(10) not null
)
create table item(
buyer varchar(10) null,
seller varchar(10) not null,
startprice numeric(5) not null,
description char(22) not null,
start_date datetime not null,
end_date datetime not null,
seller char(10) not null,
item_nummer numeric(9) not null,
constraint fk_user foreign key (buyer) references user (name)
)
Basically what the rule im trying to make here is:
Column buyer has NULL unless the time (start_date and end_date) is over and startprice didnt go up or increased. Then column buyer will get the name from table user who bidded on the item.
The rule is a bid too difficult for me to make, i was thinking to make a trigger, but im not sure..
Your model is incorrect. First you need a table to store the bids. Then when the auction is over, you update the highest one as the winning bid. Proably the best way is to have a job that runs once a minute and finds the winners of any newly closed auctions.
A trigger will not work on the two tables you have because triggers only fire on insert/update or delete. It would not fire because the time is past. Further triggers are an advanced technique and a db beginner should avoid them as you can do horrendous damage with a badly written trigger.
You could have a trigger that works on insert to the bids table, that updates the bid to be the winner and takes that status away from the previous winner. Then you simply stop accepting new bids at the time the auction is over. Your application could show the bidder who is marked as the winner as the elader if the auction is till open and teh winner if it is closed.
There are some initial problems with your schema that need addressed before tackling your question. Here are changes I would make to significantly ease the implementation of the answer:
-- Added brackets around User b/c "user" is a reserved keyword
-- Added INT Identity PK to [User]
CREATE TABLE [user]
(
UserId INT NOT NULL
IDENTITY
PRIMARY KEY
, name CHAR(10) NOT NULL
, lastname CHAR(10) NOT NULL
)
/* changed item_nummer (I'm not sure what a nummer is...) to ItemId int not null identity primary key
Removed duplicate Seller columns and buyer column
Replaced buyer/seller columns with FK references to [User].UserId
Add currentBid to capture current bid
Added CurrentHighBidderId
Added WinningBidderId as computed column
*/
CREATE TABLE item
(
ItemId INT NOT NULL
IDENTITY
PRIMARY KEY
, SellerId INT NOT NULL
FOREIGN KEY REFERENCES [User] ( UserId )
, CurrentHighBidderId INT NULL
FOREIGN KEY REFERENCES [User] ( UserId )
, CurrentBid MONEY NOT NULL
, StartPrice NUMERIC(5) NOT NULL
, Description CHAR(22) NOT NULL
, StartDate DATETIME NOT NULL
, EndDate DATETIME NOT NULL
)
go
ALTER TABLE dbo.item ADD
WinningBidderId AS CASE WHEN EndDate < CURRENT_TIMESTAMP
AND currentBid > StartPrice THEN CurrentHighBidderId ELSE NULL END
GO
With the additional columns a computed column can return the correct information. If you must return the winner's name instead of id, then you could keep the schema above the same, add an additional column to store the user's name, populate it with a trigger and keep the computed column to conditionally show/not show the winner..