I am creating a table that has two values that are both primary and foreign at the same time. I do not know how to create them in SQL. Here is what I did but I get the error, there must only be one primary key. what is the correct way?
CREATE TABLE movie_director(
director_id CHAR(8)
constraint pk_director_id_movie_director
PRIMARY KEY
constraint fk_director_id_movie_director
REFERENCES director,
movie_id VARCHAR(30)
constraint pk_movie_id_movie_director
PRIMARY KEY
constraint fk_movie_id_movie_director
REFERENCES movie
)
What you seem to be looking for is a compound primary key. Change your table definition to something like the following:
CREATE TABLE movie_director(
director_id CHAR(8)
constraint fk_director_id_movie_director
REFERENCES director,
movie_id VARCHAR(30)
constraint fk_movie_id_movie_director
REFERENCES movie,
CONSTRAINT PK_MOVIE_DIRECTOR
PRIMARY KEY (DIRECTOR_ID, MOVIE_ID));
Your error seems pretty clear. There can only be one PRIMARY KEY on a table.
You need to create a COMPOUND PRIMARY KEY which consists of two columns (director_id,movie_id).
From wikipedia:
In database design, a compound key is a key that consists of two or more attributes that uniquely identify an entity occurrence.
Related
So i have a table, that takes a nickname as foreign key and a id to form a primary key:
CREATE TABLE Character(
Nickname TEXT,
CONSTRAINT person_pk PRIMARY KEY(Nickname)
);
CREATE TABLE POSTING(
PostingID BIGINT UNIQUE,
Nickname TEXT,
CONSTRAINT posting_fk FOREIGN KEY(Nickname) REFERENCES Person(Nickname),
CONSTRAINT postings_pk PRIMARY KEY(PostingID, Nickname)
);
So far, so good. However, whenever i try to get now the primary key from posting, it tells me that: " there is no unique constraint matching given keys for referenced table "information"".
CREATE TABLE INFORMATION(
InformationID BIGINT,
PostingID BIGINT,
CONSTRAINT informations_fk FOREIGN KEY(PostingID) REFERENCES POSTING(PostingID),
CONSTRAINT informations_pk PRIMARY KEY(InformationID, PostingID)
);
CREATE TABLE DATA(
InformationID BIGINT,
Link TEXT NOT NULL,
CONSTRAINT data_fk FOREIGN KEY(InformationID) REFERENCES INFORMATION(InformationID),
CONSTRAINT datas_pk PRIMARY KEY(InformationID)
);
However, if i change in the table Information the InformationID to unique, the error disappears. Is that the correct way of doing things?
CREATE TABLE INFORMATION(
InformationID BIGINT UNIQUE,
PostingID BIGINT,
CONSTRAINT informations_fk FOREIGN KEY(PostingID) REFERENCES POSTING(PostingID),
CONSTRAINT informations_pk PRIMARY KEY(InformationID, PostingID)
);
Thanks in advance everyone!
Either the primary key for information should be only informationid, or data must include postingid and the foreign key to information is defined on both columns.
Hard to say without knowing your data, but I suspect the former solution to be the correct one.
I am pretty new to SQL and I have a problem. I want to make a recursive relationship (a table that relates to itself), but I get an error when I try to execute my code. It's working fine without the Coordinator_Office_ID foreign key.
The error is:
The number of columns in the foreign-key referencing list is not equal
to the number of columns in the referenced list.
Create table Logistican (
Office_ID Number(10) Constraint nb_office Not NULL,
Worker_ID Number(15) Constraint lg_worker not null,
Name_logistican Varchar(20),
Room Varchar(10) constraint log_room UNIQUE,
Coordinator_Office_ID Integer,
Primary key (Office_ID, Worker_ID),
Constraint work_id Foreign key (Worker_ID) References worker(worker_ID) on delete cascade,
Constraint lg_cord_id Foreign key (Coordinator_Office_ID) References Logistican(Office_ID)
);
Yes, that's cause you have defined composite primary key like Primary key (Office_ID, Worker_ID) and thus your FK should include both of them else it will result in PFD (partial functional dependency)
Add the constraint with alter table:
Create table Logistican (
Office_ID Number(10) Constraint nb_office Not NULL,
Worker_ID Number(15) Constraint lg_worker not null,
Name_logistican Varchar(20),
Room Varchar(10) constraint log_room UNIQUE,
Coordinator_Office_ID Integer,
Primary key (Office_ID, Worker_ID),
Constraint work_id Foreign key (Worker_ID) References worker(worker_ID) on delete cascade
);
alter table Logistican
add Constraint lg_cord_id
Foreign key (Coordinator_Office_ID, Worker_Id) References Logistican(Office_ID, Worker_Id);
The relationship needs all elements of the primary key to be valid. I'm not sure if it needs to be a separate statement in Oracle.
I have two tables:
Article
Subscription
In the Article table I have two columns that make up the primary key: id, sl. In the Subscription table I have a foreign key 'idsl`.
I use this constraint :
constraint FK_idsl
foreign key (idsl) references CSS_SubscriptionGroup(id, sl)
But when I run the query, I getting this error:
Number of referencing columns in foreign key differs from number of referenced columns, table X
In Article Table I have two fields that are the primary key: id,sl. In the Subscription Table I have a foreign key 'idsl`
This design is broken - it is apparent that the composite primary key in Article(id, sl) has been mangled into a single compound foreign key in table Subscription. This isn't a good idea.
Instead, you will need to change the design of table Subscription to include separate columns for both id and sl, of the same type as the Article Table, and then create a composite foreign key consisting of both columns, referencing Article in the same order as the primary key, e.g:
CREATE TABLE Article
(
id INT NOT NULL,
sl VARCHAR(50) NOT NULL,
-- Other Columns
CONSTRAINT PK_Article PRIMARY KEY(id, sl) -- composite primary key
);
CREATE TABLE Subscription
(
-- Other columns
id INT NOT NULL, -- Same type as Article.id
sl VARCHAR(50) NOT NULL, -- Same type as Article.sl
CONSTRAINT FK_Subscription_Article FOREIGN KEY(id, sl)
REFERENCES Article(id, sl) -- Same order as Article PK
);
Edit
One thing to consider here is that by convention a column named table.id or table.tableid should be unique, and is the primary key for the table. However, since table Article requires an additional column sl in the primary key, it implies that id isn't unique.
correct syntax for relation:
CONSTRAINT FK_OtherTable_ParentTable
FOREIGN KEY(OrderId, CompanyId) REFERENCES dbo.ParentTable(OrderId, CompanyId)
You must try like this:
constraint FK_idsl foreign key (id,sl) references CSS_SubscriptionGroup(id,sl)
I am currently making a database back end system on an airport, using sql through the phpmyadmin server. The criteria is not meant to be perfect but one of the ideas behind the queries is to imagine that either a customer or flight dispatch officer might be looking at the tables. I was wondering if it was possible to reference a primary key as a foreign key across 2 or more tables. In the example below, I want to reference the model number as a foreign key in the bottom 2 tables. I have ensured that the type and character count are the same.
CREATE TABLE Aircraft_Model
(Model_Number varchar (12) NOT NULL,
seat_capacity int (3),
CONSTRAINT pk7 primary key (Model_Number));
CREATE TABLE Licence_type
(Rank varchar (25) NOT NULL,
Model_Number varchar (12),
CONSTRAINT pk9 primary key (Rank));
CREATE TABLE Aircraft
(Aircraft_ID varchar (4) NOT NULL,
Model_Number varchar(12),
airport_base text(13),
CONSTRAINT pk1 PRIMARY KEY (Aircraft_ID));
Is this possible? I only want the database to be able to perform about 12-15 simple queries.
Would the syntax of adding a foreign key be something like this?
ALTER TABLE Aircraft
ADD CONSTRAINT fk1 FOREIGN KEY(Model_Number)
REFERENCES Aircraft_Model
Does the same foreign key being referenced from a separate table such as Licence_type need a separate constraint to be added or can it be added from the same one with the same fk1 number?
I was wondering if it was possible to reference a primary key as a
foreign key across 2 or more tables.
If you mean, "Can two or more tables have foreign keys that reference the same column?", then, yes, you can do that. This seems to be what you mean, but it's not what most people mean when they talk about "a foreign key across 2 or more tables".
Declare two different, separate constraints.
ALTER TABLE Aircraft
ADD CONSTRAINT fk1 FOREIGN KEY(Model_Number)
REFERENCES Aircraft_Model (Model_Number);
ALTER TABLE License_Type
ADD CONSTRAINT fk2 FOREIGN KEY(Model_Number)
REFERENCES Aircraft_Model (Model_Number);
I have two parent tables: Treatment and Visit.
Treatment table:
create table Treatment (
TreatCode CHAR(6) constraint cTreatCodeNN not null,
Name VARCHAR2(20),
constraint cTreatCodePK primary key (TreatCode),
);
Visit table:
create table Visit (
SlotNum NUMBER(2),
DateVisit DATE,
ActualArrivalTime DATE,
constraint cVisitSlotDatePK primary key (SlotNum, DateVisit)
);
Now I try to create a child table:
create table Visit_Treat (
TreatCode constraint cTreatCodeFK references Treatment(TreatCode),
SlotNum constraint cSlotNumFK references Visit(SlotNum),
DateVisit constraint cDateFK references Visit(DateVisit),
constraint cVisitTreatPK primary key (SlotNum, TreatCode, DateVisit)
);
Everything executes fine till the 3 line. Starting from the 3rd line, i.e. SlotNum constraint ... there is a message: no matching unique or primary key. There was already a similar question, but i did not quite get the logic to apply in my case. I reference each column one by one, and it works for the Treatment table parent. How should i correct reference Visit table parent?
CONSTRAINT fk_column
FOREIGN KEY (column1, column2, ... column_n)
REFERENCES parent_table (column1, column2, ... column_n)
in your case
create table Visit_Treat (
TreatCode CHAR(6) constraint cTreatCodeFK references Treatment(TreatCode),
SlotNum NUMBER(2),
DateVisit DATE,
constraint cVisitTreatPK primary key (SlotNum, TreatCode, DateVisit),
constraint fk_slotnumDatevisit FOREIGN KEY(SlotNum,DateVisit)
references Visit(SlotNum,DateVisit)
);
A foreign key must reference the primary key of the parent table - the entire primary key. In your case, the Visit table's primary key is SlotNum, DateVisit but the foreign key from Visit_Treat only references SlotNum.
You have two good options:
Add a DateVisit column to Visit_Treat and have the foreign key be SlotNum, DateVisit, referencing SlotNum, DateVisit in Visit.
Create a non-business primary key on Visit (for example a column named VisitID of type NUMBER, fed by a sequence), add a VisitID column to Visit_Treat, and make that the foreign key.
And two bad options:
Change the Visit primary key to be only SlotNum so your Visit_Treat foreign key will work. This probably isn't what you want.
Don't use a foreign key. I don't recommend this option. If you're having trouble setting up a foreign key that you know should exist, it generally means a design problem.