I have a SQL Server table with two columns id:INT and flagged:BOOLEAN. Is it possible to add a constraint that ensures that there is only one entry for (id=a, flagged=b) where b = 1?
For example:
ok
(id=1, flagged=1)
(id=1, flagged=0)
(id=1, flagged=0)
not ok
(id=1, flagged=1)
(id=1, flagged=1)
(id=1, flagged=0)
Create Unique Index with filter:
CREATE UNIQUE INDEX idx_name ON your_table(id)
WHERE flagged=1;
Demo:
SqlFiddleDemo
CREATE TABLE your_table(id INT, flagged INT);
CREATE UNIQUE INDEX idx_name ON your_table(id)
WHERE flagged=1;
INSERT INTO your_table(id, flagged)
VALUES (1, 0), (1,1), (1,0);
INSERT INTO your_table(id, flagged) -- will fail
VALUES (1,1);
/* Cannot insert duplicate key row in object 'dbo.your_table'
with unique index 'idx_name'. The duplicate key value is (1).*/
Related
I want not to allow my DB user to enter bigger dates than 2017-03-18. How can add this constraint to my table?
Is this Correct?
(Year([ContractEnd])<2017) and (Month([ContractEnd])<03) and (Day([ContractEnd])<18)
You can add a constraint like that to an existing table like so:
alter table t add constraint chk_ContractEnd_lt_20170319
check (ContractEnd<'20170319');
rextester demo: http://rextester.com/FQWFMI88817
create table t (
id int not null identity(1,1)
, ContractEnd date
/* at table creation */
, constraint chk_ContractEnd_lt_20170319 check (ContractEnd<'20170319')
)
alter table t drop constraint chk_ContractEnd_lt_20170319;
/* to existing table */
alter table t add constraint chk_ContractEnd_lt_20170319
check (ContractEnd<='20170318');
insert into t values ('20161231')
insert into t values ('20170318')
/* all good */
insert into t values ('20170319')
/* -- Error, constraint violation */
Try
[ContractEnd] DATE CHECK ([ContractEnd] <= '20170318')
Suppose B and C are both subclass and A is a superclass. B and C can not have same id (disjoint)
CREATE TABLE a(id integer primary key);
CREATE TABLE b(id integer references a(id));
CREATE TABLE c(id integer references a(id));
insert into a values('1');
insert into a values('2');
insert into b values('1');
insert into c values('2');
Could I use a trigger to prevent the same id appearing in tables B and C?
"b and c can not have same id"
So you want to enforce a mutually exclusive relationship. In data modelling this is called an arc. Find out more.
We can implement an arc between tables without triggers by using a type column to distinguish the sub-types like this:
create table a (
id integer primary key
, type varchar2(3) not null check (type in ( 'B', 'C'))
, constraint a_uk unique (id, type)
);
create table b (
id integer
, type varchar2(3) not null check (type = 'B')
, constraint b_a_fk foreign key (id, type) references a (id, type)
);
create table b (
id integer
, type varchar2(3) not null check (type = 'C')
, constraint c_a_fk foreign key (id, type) references a (id, type)
);
The super-type table has a unique key in addition to its primary key; this provides a reference point for foreign keys on the sub-type tables. We still keep the primary key to insure uniqueness of id.
The sub-type tables have a redundant instance of the type column, redundant because it contains a fixed value. But this is necessary to reference the two columns of the compound unique key (and not the primary key, as is more usual).
This combination of keys ensures that if the super-type table has a record id=1, type='B' there can be no record in sub-type table C where id=1.
Design wise this is not good but we can do it using the below snippet. You can create a similar trigger on table b
CREATE TABLE a(id integer primary key);
CREATE TABLE b(id integer references a(id));
CREATE TABLE c(id integer references a(id));
create or replace trigger table_c_trigger before insert on c for each row
declare
counter number:=0;
begin
select count(*) into counter from b where id=:new.id;
if counter<>0 then
raise_application_error(-20001, 'values cant overlap between c and b');
end if;
end;
insert into a values('1');
insert into a values('2');
insert into b values('1');
insert into b values('2');
insert into c values('2');
You can use Oracle Sequence:
CREATE SEQUENCE multi_table_seq;
INSERT INTO A VALUE(1);
INSERT INTO A VALUE(2);
INSERT INTO B VALUE(multi_table_seq.NEXTVAL()); -- Will insert 1 in table B
INSERT INTO C VALUE(multi_table_seq.NEXTVAL()); -- Will insert 2 in table C
...
With trigger:
-- Table B
CREATE TRIGGER TRG_BEFORE_INSERT_B -- Trigger name
BEFORE INSERT -- When trigger is fire
ON A -- Table name
DECLARE
v_id NUMBER;
BEGIN
v_id := multi_table_seq.NEXTVAL();
BEGIN
SELECT TRUE FROM C WHERE id = v_id;
RAISE_APPLICATION_ERROR(-20010, v_id || ' already exists in table C');
EXCEPTION WHEN NO_DATA_FOUND -- Do nothing if not found
END;
END;
And same trigger for table C who check if id exists in table B
Is there any way to add a constraint on a column that is an array to limit it's length? I want these arrays to be no longer than 6. And yes, I understand that often a new table is better than storing in an array but I am in a situation where an array makes more sense.
You can add a CHECK constraint to the table definition:
CREATE TABLE my_table (
id serial PRIMARY KEY,
arr int[] CHECK (array_length(arr, 1) < 7),
...
);
If the table already exists, you can add the constraint with ALTER TABLE:
ALTER TABLE my_table ADD CONSTRAINT arr_len CHECK (array_length(arr, 1) < 7);
I have a table like this :
create table ReceptionR1
(
numOrdre char(20) not null,
dateDepot datetime null,
...
)
I want to increment my id field (numOrdre) like '225/2015','226/2015',...,'1/2016' etc. What should I have to do for that?
2015 means the actual year.
Please let me know any possible way.
You really, and I mean Really don't want to do such a thing, especially as your primary key. You better use a simple int identity column for you primary key and add a non nullable create date column of type datetime2 with a default value of sysDateTime().
Create the increment number by year either as a calculated column or by using an instead of insert trigger (if you don't want it to be re-calculated each time). This can be done fairly easy with the use of row_number function.
As everyone else has said - don't use this as your primary key! But you could do the following, if you're on SQL Server 2012 or newer:
-- step 1 - create a sequence
CREATE SEQUENCE dbo.SeqOrderNo AS INT
START WITH 1001 -- start with whatever value you need
INCREMENT BY 1
NO CYCLE
NO CACHE;
-- create your table - use INT IDENTITY as your primary key
CREATE TABLE dbo.ReceptionR1
(
ID INT IDENTITY
CONSTRAINT PK_ReceptionR1 PRIMARY KEY CLUSTERED,
dateDepot DATE NOT NULL,
...
-- add a colum called "SeqNumber" that gets filled from the sequence
SeqNumber INT,
-- you can add a *computed* column here
OrderNo = CAST(YEAR(dateDepot) AS VARCHAR(4)) + '/' + CAST(SeqNumber AS VARCHAR(4))
)
So now, when you insert a row, it has a proper and well defined primary key (ID), and when you fill the SeqNumber with
INSERT INTO dbo.ReceptionR1 (dateDepot, SeqNumber)
VALUES (SYSDATETIME(), NEXT VALUE FOR dbo.SeqOrderNo)
then the SeqNumber column gets the next value for the sequence, and the OrderNo computed column gets filled with 2015/1001, 2015/1002 and so forth.
Now when 2016 comes around, you just reset the sequence back to a starting value:
ALTER SEQUENCE dbo.SeqOrderNo RESTART WITH 1000;
and you're done - the rest of your solution works as before.
If you want to make sure you never accidentally insert a duplicate value, you can even put a unique index on your OrderNo column in your table.
Once more, you cannot use the combo field as your primary key. This solution sort or works on earlier versions of SQL and calculates the new annual YearlySeq counter automatically - but you had better have an index on dateDepot and you might still have issues if there are many, many (100's of thousands) of rows per year.
In short: fight the requirement.
Given
create table dbo.ReceptionR1
(
ReceptionR1ID INT IDENTITY PRIMARY KEY,
YearlySeq INT ,
dateDepot datetime DEFAULT (GETDATE()) ,
somethingElse varchar(99) null,
numOrdre as LTRIM(STR(YearlySeq)) + '/' + CONVERT(CHAR(4),dateDepot,111)
)
GO
CREATE TRIGGER R1Insert on dbo.ReceptionR1 for INSERT
as
UPDATE tt SET YearlySeq = ISNULL(ii.ReceptionR1ID - (SELECT MIN(ReceptionR1ID) FROM dbo.ReceptionR1 xr WHERE DATEPART(year,xr.dateDepot) = DATEPART(year,ii.dateDepot) and xr.ReceptionR1ID <> ii.ReceptionR1ID ),0) + 1
FROM dbo.ReceptionR1 tt
JOIN inserted ii on ii.ReceptionR1ID = tt.ReceptionR1ID
GO
insert into ReceptionR1 (somethingElse) values ('dumb')
insert into ReceptionR1 (somethingElse) values ('requirements')
insert into ReceptionR1 (somethingElse) values ('lead')
insert into ReceptionR1 (somethingElse) values ('to')
insert into ReceptionR1 (somethingElse) values ('big')
insert into ReceptionR1 (somethingElse) values ('problems')
insert into ReceptionR1 (somethingElse) values ('later')
select * from ReceptionR1
2nd Edit: The source code for the involved function is as follows:
ALTER FUNCTION [Fileserver].[fn_CheckSingleFileSource] ( #fileId INT )
RETURNS INT
AS
BEGIN
-- Declare the return variable here
DECLARE #sourceCount INT ;
-- Add the T-SQL statements to compute the return value here
SELECT #sourceCount = COUNT(*)
FROM Fileserver.FileUri
WHERE FileId = #fileId
AND FileUriTypeId = Fileserver.fn_Const_SourceFileUriTypeId() ;
-- Return the result of the function
RETURN #sourceCount ;
END
Edit: The example table is a simplification. I need this to work as a Scaler Function / CHECK CONSTRAINT operation. The real-world arrangement is not so simple.
Original Question: Assume the following table named FileUri
FileUriId, FileId, FileTypeId
I need to write a check constraint such that FileId are unique for a FileTypeId of 1. You could insert the same FileId as much as you want, but only a single row where FileTypeId is 1.
The approach that DIDN'T work:
1) dbo.fn_CheckFileTypeId returns INT with following logic: SELECT Count(FileId) FROM FileUri WHERE FileTypeId = 1
2) ALTER TABLE FileUri ADD CONSTRAINT CK_FileUri_FileTypeId CHECK dbo.fn_CheckFileTypeId(FileId) <= 1
When I insert FileId 1, FileTypeId 1 twice, the second insert is allowed.
Thanks SO!
You need to create a filtered unique index (SQL Server 2008)
CREATE UNIQUE NONCLUSTERED INDEX ix ON YourTable(FileId) WHERE FileTypeId=1
or simulate this with an indexed view (2000 and 2005)
CREATE VIEW dbo.UniqueConstraintView
WITH SCHEMABINDING
AS
SELECT FileId
FROM dbo.YourTable
WHERE FileTypeId = 1
GO
CREATE UNIQUE CLUSTERED INDEX ix ON dbo.UniqueConstraintView(FileId)
Why don't you make FieldTypeID and Field both the primary key of the table?
Or at least a Unique Index on the table. That should solve your problem.