I have this table:
CREATE TABLE cars_info.cars
(
id SERIAL,
owner_id INTEGER,
brand VARCHAR(50) NOT NULL,
model VARCHAR(50) NOT NULL,
color VARCHAR(50) NOT NULL,
register_number VARCHAR(50) NOT NULL,
created DATE NOT NULL,
PRIMARY KEY(id, brand, model, color, register_number, created),
CONSTRAINT fk_owner_id
FOREIGN KEY(owner_id)
REFERENCES persons_info.persons(id)
);
But when I tried create another table like this:
CREATE TABLE cars_info.violations
(
id SERIAL PRIMARY KEY,
car_id INTEGER NOT NULL,
message VARCHAR(100) NOT NULL,
active BOOLEAN NOT NULL,
CONSTRAINT fk_car_id
FOREIGN KEY(car_id)
REFERENCES cars_info.cars(id)
);
I get an error about that
Target external table "cars" does not have a unique constraint corresponding to the given keys
How can I fix that? I'm a beginner in SQL and don't know how to go about googling that
Your primary key definition for cars
PRIMARY KEY(id, brand, model, color, register_number, created)
makes no sense: The id column, being serial, is itself unique and it alone should be the primary key.
Delete your primary key definition and change the id column definition to:
id serial not null primary key
Unrelated, but best practice is to name table in the singular; name your tables car and violation rather than cars and violations
Related
I have 2 tables in my database:
CREATE TABLE Apartment
(
StreetName char(50) not null,
Number Integer not null,
Door Integer not null,
Type char(30) not null,
SizeSquareMeter Integer not null,
NID Integer not null FOREIGN KEY REFERENCES Neighborhood(NID)
CONSTRAINT Address PRIMARY KEY (StreetName, Number, Door)
);
CREATE TABLE Resident
(
RID Integer not null PRIMARY KEY,
FirstName varchar(30) not null,
LastName varchar(30) not null,
BirthDate date not null,
Address
);
Now the primary key in apartment is Address and is based on constraint. I want to create a foreign key Address in the Resident table referencing the
primary key Address in the Apartment table.
How can I do that?
Since your primary key in Apartment is made up from three columns, any table wanting to reference Apartment will also need to have ALL three columns to establish a foreign key link.
So you need to change your Resident table to:
CREATE TABLE Resident
(
RID Integer not null PRIMARY KEY,
FirstName varchar(30) not null,
LastName varchar(30) not null,
BirthDate date not null,
StreetName char(50) not null,
Number Integer not null,
Door Integer not null,
);
and then you can add the foreign key constraint:
ALTER TABLE Resident
ADD CONSTRAINT FK_Resident_Apartment
FOREIGN KEY (StreetName, Number, Door) REFERENCES Apartment (StreetName, Number, Door);
The other option would be to add a surrogate column (an artificial, additional column) to Apartment - either as primary key, or (for SQL Server) at least with a unique constraint - so that you could establish the FK link to that surrogate column (using that one, single column - instead of having to replicate three columns of "real" data)
I'm new to SQL and there are a lot of things going on that I still don't seem to quite understand. I have the following table
CREATE TABLE Person
(
First_Name varchar(20) NOT NULL,
Name varchar(20) NOT NULL,
Address varchar(50) NOT NULL,
PRIMARY KEY (First_Name, Name, Address)
);
I know want to create another table that has the primary key from the table Person as foreign key and also as primary key:
CREATE TABLE Purchase
(
No_Installments int,
Rate int,
Person varchar(50) NOT NULL PRIMARY KEY,
CONSTRAINT PFK
FOREIGN KEY (Person) REFERENCES Person (First_Name, Name, Address)
);
For some reason this doesn't work and I get an error every time. I've already looked up the other threads here on stackoverflow, but they don't really seem to help me. What am I doing wrong?
If you have a compound PK made up from three columns, then any child table that wants to establish a foreign key relationship must ALSO have all those 3 columns and use all 3 columns to establish the FK relationship.
FK-PK relationship is an all or nothing proposal - you cannot reference only parts of a primary key - either you reference all columns - or you don't reference.
CREATE TABLE Purchase
(
No_Installments int,
Rate int,
Person varchar(50) NOT NULL PRIMARY KEY,
First_Name varchar(20) NOT NULL,
Name varchar(20) NOT NULL,
Address varchar(50) NOT NULL,
CONSTRAINT PFK
FOREIGN KEY (First_Name, Name, Address)
REFERENCES Person (First_Name, Name, Address)
);
Have an integer primary key, using identity, auto_increment, serial or whatever for your database:
CREATE TABLE Person (
PersonId int identity PRIMARY KEY
First_Name varchar(20) NOT NULL,
Name varchar(20) NOT NULL,
Address varchar(50) NOT NULL,
CONSTRAINT unq_person_3 UNIQUE (First_Name, Name, Address)
);
Then use the identity column for the reference:
CREATE TABLE Purchase (
PurchaseId int identity PRIMARY KEY,
No_Installments int,
Rate int,
PersonId int,
CONSTRAINT PFK
FOREIGN KEY (PersonId) REFERENCES Person (PersonId)
);
Notes:
You really don't want to have to deal with a composite primary key. Have you thought about what the joins will look like?
You don't want a primary key where the values are subject to change. What happens when someone changes his/her name? When someone moves?
Person should not be the primary key in Purchases. Are you only allowing someone to make one purchase?
As noted initially, how you generate such a column varies by database; identity happens to be the way that SQL Server does this.
You probably want to assign a unique ID to each person, not relying on their name to be unique or for an address to be required. That ID will be your Primary key and foreign key. Your purchase table should also have its own id for its primary key -- otherwise because primary keys must be unique, each person can only have one purchase.
CREATE TABLE Person (
id serial NOT NULL,
First_Name varchar(20) NOT NULL,
Name varchar(20) NOT NULL,
Address varchar(50) NOT NULL,
PRIMARY KEY (id));
CREATE TABLE Purchase (
id serial NOT NULL,
No_Installments int,
Rate int,
Person int NOT NULL,
FOREIGN KEY (Person) REFERENCES Person (id),
PRIMARY KEY (id));
I'm in a bit of a mix right now, I have a Table called Avatars, which has a foreign key called Family. Now, in the family table, I have two Foreign Keys called Mother and Father - Now this is the confusing bit, in both the Mother and Father Tables, there is a Foreign key called Avatar_ID which is of course the Primary Key to the Avatars table. I'm not sure if that's even allowed in SQL PLUS.
Whenever I try and enter the tables 'Family, Mother or Father', I keep getting the error:ORA-02291: integrity constraint (SG304.FK_FATHER_ID) violated - parent key not found.
Is there any way around this? Or will I have to change my code completely? A sample of the code is below.
CREATE TABLE Avatars (
Avatar_ID VARCHAR(10) NOT NULL,
Avatar_Name VARCHAR(30),
AvA_DOB DATE,
Age VARCHAR(30),
Gender VARCHAR(30),
Strength_Indicated INT,
Hoard INT,
Avatar_Level VARCHAR(30),
Skill VARCHAR(30),
Original_Owner VARCHAR(30),
Family_ID VARCHAR(10) NOT NULL,
Species_ID VARCHAR(10) NOT NULL,
Inventory_ID VARCHAR(30) NOT NULL,
Weapon_ID VARCHAR(10),
Player_ID VARCHAR(10) NOT NULL,
PRIMARY KEY (Avatar_ID));
CREATE TABLE Family (
Family_ID VARCHAR(10) NOT NULL,
Mother_ID VARCHAR(10) NOT NULL,
Father_ID VARCHAR(10) NOT NULL,
primary key(Family_ID)
);
CREATE TABLE Mother (
Mother_ID VARCHAR(10) NOT NULL,
Avatar_ID VARCHAR(10) NOT NULL,
primary key(Mother_ID)
);
CREATE TABLE Father (
Father_ID VARCHAR(10) NOT NULL,
Avatar_ID VARCHAR(10) NOT NULL,
primary key(Father_ID)
);
ALTER TABLE Avatars
ADD CONSTRAINT fk_Family_ID
FOREIGN KEY (Family_ID)
REFERENCES Family(Family_ID);
ALTER TABLE Family
ADD CONSTRAINT fk_Mother_ID
FOREIGN KEY (Mother_ID)
REFERENCES Mother(Mother_ID);
ALTER TABLE Family
ADD CONSTRAINT fk_Father_ID
FOREIGN KEY (Father_ID)
REFERENCES Father(Father_ID);
ALTER TABLE Father
ADD CONSTRAINT fk_Avatar_ID
FOREIGN KEY (Avatar_ID)
REFERENCES Avatars(Avatar_ID);
ALTER TABLE Mother
ADD CONSTRAINT fk_Avatars_ID
FOREIGN KEY (Avatar_ID)
REFERENCES Avatars(Avatar_ID);
INSERT INTO Avatars (Avatar_ID,Avatar_Name,AvA_DOB,Age,Gender,Strength_Indicated,Hoard,Avatar_Level, Skill, Original_Owner, Family_ID,Species_ID,Inventory_ID,Player_ID) VALUES
('Ava01','Verda','20-JAN-2014','1 year 2 months','Female','100','20','Master','Leader',' - ',' - ','DRA1','MasterInventory','Player07');
Thanks in advance for any help given! (:
Foreign key refers to a record in parent table. In your INSERT statement you are inserting value ' - ' into a column parent_id. In this error message oracle informs you that there is no record with value ' - ' in a column family_id of a table family. As I can understand, you are trying to use ' - ' as 'absence of value'. There is special value for that - NULL. So you need to write your statement as:
INSERT INTO Avatars (Avatar_ID, Avatar_Name, AvA_DOB,
Age, Gender, Strength_Indicated, Hoard, Avatar_Level, Skill,
Original_Owner, Family_ID, Species_ID, Inventory_ID, Player_ID)
VALUES ('Ava01', 'Verda', '20-JAN-2014', '1 year 2 months' ,'Female',
'100', '20', 'Master', 'Leader', NULL, NULL, 'DRA1',
'MasterInventory', 'Player07');
Also I can recommend some changes to your schema. First of all, use number data type for primary keys - it allows you to use sequences to generate unique values. Also, I don't know details of the problem, but "family relations" in your tables look a bit complicated. You can describe it in a single table:
create table family_tree (
person_id number primary key,
father_id number,
mother_id number,
sex char(1),
name varchar2(50),
family_name varchar2(50));
add constraint fk_mother_id foreign key (mother_id)
references family_tree (person_id);
add constraint fk_father_id foreign key (father_id)
references family_tree (person_id);
CREATE TABLE sampProduct
(
Product_ID VARCHAR(15) NOT NULL,
Supplier_ID INT NOT NULL,
Category_ID INT NOT NULL,
Unit_Price DECIMAL(10, 2)
PRIMARY KEY(Product_ID)
)
CREATE TABLE sampMachine
(
M_Product_ID VARCHAR(15) NOT NULL,
Serial_No VARCHAR(15) NOT NULL,
Machine_Model VARCHAR(20),
PRIMARY KEY(M_Product_ID, Serial_No),
FOREIGN KEY(M_Product_ID) REFERENCES sampProduct(Product_ID)
)
CREATE TABLE sampService
(
Service_ID VARCHAR(15) NOT NULL,
Serial_No VARCHAR(15) NOT NULL,
Complaint VARCHAR(40) NOT NULL,
PRIMARY KEY(Service_ID),
FOREIGN KEY(Serial_No) REFERENCES sampMachine(Serial_No)
)
Machine is a subtype of Product. M_ProductID is referencing the primary key of the parent table Product by this key. And Serial_No is used to uniquely identify a Machine. The problem is, I want to create a foreign key from Serial_No into the Service table, since I want to track the serial numbers of the machine (this is because, for example, we can have many machine for each model or type, but each of them has their unique serial numbers), but there is an error for the creation. Can you help me out?
One of the requirements for creating a foreign key is that the table you reference must have a unique key on the columns you want referenced. So in your example in order for it to work you would need a unique key on sampMachine (Serial_No) so that you could create foreign keys to it using just Serial_No. The way you have it now you would need to use M_Product_Id in the table sampService and add it to the foreign key definition.
create table sampService(
M_Product_ID varchar(15) not null,
Service_ID varchar(15) not null,
Serial_No varchar(15) not null,
Complaint varchar(40) not null,
primary key (Service_ID),
foreign key (Serial_No) references sampMachine(m_Product_Id, Serial_No)
)
I have a one-to-many relationship between two classes for this situation. I have a swimming competition and that competition can have x swimmers.
How can I create an SQL table for this, I know I will have to use the Primary Key of Swimmers as a foreign key in the Swimming competition but I have no idea how to represent the correct number of attributes since it's unknown.
This is called a m:n relationship and usually solved with a mapping table.
Something like this:
create table swimmer
(
id integer not null primary key,
lastname varchar(100) not null,
firstname varchar(100)
)
create table competition
(
id integer not null primary key,
name varchar(50) not null,
comp_date date not null
)
create table participant
(
swimmer_id integer not null,
competition_id integer not null,
rank_in_competetion integer,
primary key (swimmer_id, competition_id),
constraint fk_participant_swimmer (swimmer_id) references swimmer(id),
constraint fk_participant_competition (competition_id) references competition(id)
)