I am creating a database containing video rental information. In the copy table i have the film number (FNr) and the copy number (cpyNr) as primary key (there is more, but to simplify the problem i have removed them). In the second table, rent, the film number (FNr),copy number (cpyNr) and the customer number (CNr) is part of the key. The copy number is referenced from the copy table. Film number and customer number will be referenced from elsewhere, but is not relevant for the question and i have removed them for simplicity.
The problem is, when i run the code below as it is now, it doesn't work. I get a foreign key constrain fails.
drop database if exists video;
create database video;
use video;
CREATE TABLE copy
(
FNr INT,
cpyNr INT,
CONSTRAINT copyPK
PRIMARY KEY (FNr,cpyNr)
);
CREATE TABLE rent
(
FNr INT,
cpyNr INT,
CNr INT,
CONSTRAINT rentPK
PRIMARY KEY (FNr,cpyNr,CNr),
CONSTRAINT copyPK FOREIGN KEY (cpyNr)
REFERENCES copy(cpyNr)
);
What does work however is if i change the order of the columns in the primary key of copy to
PRIMARY KEY (cpyNr,FNr)
it does work, but i cannot understand why.
Related
I am creating web-app for database management. Database can be created using diagrams ER.
Here is screen from my app:
As you can see this pseudo example shows 4x types of cases:
1) Primary key --> Primary key (1:1)
2) Unique key --> Unique key (1:1)
3) Primary key consisting of two fields --> Primary key consisting of two fields (1:1)
4) Unique key consisting of two fields --> Unique key consisting of two fields (1:1)
And here is my question:
Is it all true? I wonder about these double keys... Is this really a 1 to 1 relation?
Generally, I wonder about these first 2 cases too. Are there also true?
MySQL Workbench shows it is not true:
I dont know why but you can see MySQL Workbench shows this is one to many relation...
Oracle Sql Developer:
Can anyone tell me when 1 to 1 relationship actually is?
Documentation shows i have right:
https://docs.oracle.com/cd/E26180_01/Platform.94/RepositoryGuide/html/s1204onetoonewithauxiliarytable01.html
but diagrams ER in MySQL Workbench and Sql Developer shows something different...
SQL code from that tables:
CREATE USER "Student" IDENTIFIED BY "null";
CREATE TABLE "Student".Table1 (
PK_FK NUMBER NOT NULL
);
CREATE TABLE "Student".Table2 (
PK NUMBER NOT NULL
);
CREATE TABLE "Student".Table3 (
PK NUMBER NOT NULL,
UK_FK NUMBER
);
CREATE TABLE "Student".Table4 (
PK NUMBER NOT NULL,
UK NUMBER
);
CREATE TABLE "Student".Table5 (
PK_1_FK NUMBER NOT NULL,
PK_2_FK NUMBER NOT NULL
);
CREATE TABLE "Student".Table6 (
PK_1 NUMBER NOT NULL,
PK_2 NUMBER NOT NULL
);
CREATE TABLE "Student".Table7 (
UK_1_FK NUMBER,
UK_2_FK NUMBER
);
CREATE TABLE "Student".Table8 (
UK_1 NUMBER,
UK_2 NUMBER
);
ALTER TABLE "Student".Table1 ADD CONSTRAINT Table1_PK PRIMARY KEY (PK_FK);
ALTER TABLE "Student".Table2 ADD CONSTRAINT Table2_PK PRIMARY KEY (PK);
ALTER TABLE "Student".Table3 ADD CONSTRAINT Table3_PK PRIMARY KEY (PK);
ALTER TABLE "Student".Table4 ADD CONSTRAINT Table4_PK PRIMARY KEY (PK);
ALTER TABLE "Student".Table5 ADD CONSTRAINT Table5_PK PRIMARY KEY (PK_1_FK, PK_2_FK);
ALTER TABLE "Student".Table6 ADD CONSTRAINT Table6_PK PRIMARY KEY (PK_1, PK_2);
ALTER TABLE "Student".Table3 ADD CONSTRAINT Table3_UK1 UNIQUE (UK_FK);
ALTER TABLE "Student".Table4 ADD CONSTRAINT Table4_UK2 UNIQUE (UK);
ALTER TABLE "Student".Table7 ADD CONSTRAINT Table7_UK3 UNIQUE (UK_1_FK, UK_2_FK);
ALTER TABLE "Student".Table8 ADD CONSTRAINT Table8_UK4 UNIQUE (UK_1, UK_2);
ALTER TABLE "Student".Table1 ADD CONSTRAINT Table1_FK1 FOREIGN KEY (PK_FK)
REFERENCES "Student".Table2 (PK);
ALTER TABLE "Student".Table3 ADD CONSTRAINT Table3_FK2 FOREIGN KEY (UK_FK)
REFERENCES "Student".Table4 (UK);
ALTER TABLE "Student".Table5 ADD CONSTRAINT Table5_FK3 FOREIGN KEY (PK_1_FK, PK_2_FK)
REFERENCES "Student".Table6 (PK_1, PK_2);
ALTER TABLE "Student".Table7 ADD CONSTRAINT Table7_FK4 FOREIGN KEY (UK_1_FK, UK_2_FK)
REFERENCES "Student".Table8 (UK_1, UK_2);
That's perfectly possible. Here's an example for PostgreSQL:
create table t1 (
a int not null,
b int not null,
constraint uq1 (a, b),
constraint fk1 foreign key (a, b) references t2 (a, b)
deferrable initially deferred
);
create table t2 (
a int not null,
b int not null,
constraint uq2 (a, b),
constraint fk2 foreign key (a, b) references t1 (a, b)
deferrable initially deferred
);
In this case t1 (a,b) is unique and references t2 (a, b) that is also unique. That's a 1:1 relationship using "composite keys".
Note: This example uses "circular references" that is a standard part of SQL, but is only implemented [to my knowledge] by PostgreSQL and Oracle. It won't run in MySQL.
A one-to-one relationship is still a master-detail relationship. One table is the owner of the identifier and the other table references it through a foreign key. This is the relationship show in the MySQL Workbench and SQL Developer pictures.
Documentation shows i have right:
You link to Oracle's documentation for ATG Repository, which is a specialist tool for representing data generically, but even there we can see from the SQL that USER_TBL is the primary table and "owns" the ID column and JOB_TBL is the auxiliary table and references the ID.
CREATE TABLE usr_tbl (
id VARCHAR(32) not null,
nam_col VARCHAR(32) null,
age_col INTEGER null,
primary key(id)
);
CREATE TABLE job_tbl (
id VARCHAR(32) not null references usr_tbl(id),
function VARCHAR(32) null,
title VARCHAR(32) null,
primary key(id)
In other words, we can have a USER without a JOB but we can't have a JOB without a USER. But a USER can have only one JOB and one JOB belongs only to ONE user.
Your diagram is wrong because it renders TABLE7 and TABLE8 as peers. But foreign keys don't work like that. One table defer to the other. When I look at your notation I can't see whether TABLE8 owns TABLE7 or TABLE7 owns TABLE8. Whereas, it's quite clear in the MySQL and Oracle diagrams. The purpose of a data model is to clarify the database design not obfuscate it.
Note, it is perfectly possible to define two tables which have foreign keys that reference each other's primary key. The trick is insert data into them. This requires deferring the foreign key constraints. I view deferred constraints as a red flag, a sign of a broken data model.
I want to know how to use a foreign key in a table,
I have a code here:
create table penerbit_buku(
id_buku char(8),
foreign key(id_buku) references buku(id_buku),
id_penerbit char(3),
foreign key(id_penerbit) references penerbit(id_penerbit)
)
Can I use this code instead:
create table penerbit_buku(
id_buku char(8) references buku(id_buku),
id_penerbit char(3) references penerbit(id_penerbit)
)
I have tried both and it succeed, is that correct?
No, MySQL parses but ignores the standard inline REFERENCES syntax.
When you declare a foreign key along with an individual column definition, it accepts the syntax as legitimate SQL, but then does not store the foreign key constraint. There's no error reported, but it's as if you didn't write the foreign key syntax at all.
You must declare foreign keys as table-level constraints (your first example above).
This is a case where MySQL is missing a feature of standard SQL. The issue was reported back in 2004, but never fixed! https://bugs.mysql.com/bug.php?id=4919
The reason for this issue is that historically, foreign key constraints were not supported by MySQL itself, but by the InnoDB storage engine, which was made by another company back then. They had to implement their own parser for CREATE TABLE and ALTER TABLE to support foreign keys, and they didn't feel like going the extra steps to support inline foreign key syntax, when table-level foreign key syntax would work.
The architect of InnoDB posted this response:
[6 Sep 2006 10:03] Heikki Tuuri
This will be fixed in MySQL foreign keys, when they are available for all table types.
The MySQL project is gradually working their way toward integrating foreign keys and similar features directly into the MySQL product. Perhaps in a few more years we'll see better support for standard FK syntax.
EXAMPLE:
CREATE TABLE Orders (
ID int NOT NULL,
Number int NOT NULL,
PersonID int,
PRIMARY KEY (ID),
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID)
);
The foreign key must be referencing a primary key in another table
create table penerbit_buku
(id_buku char(8),
id_penerbit char(3),
foreign key(id_buku) references buku(id_buku),
foreign key(id_penerbit) references penerbit(id_penerbit)
);
I would need to see your other tables to give better help in the code
You can use this:
ALTER TABLE `table1`
ADD CONSTRAINT `FK_table1_table2` FOREIGN KEY (`fk_id`) REFERENCES `table2` (`id`);
first lets look at the description of FOREIGN KEY.
A FOREIGN KEY is a key used to link two tables together.
or
A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table.
Usually a table that has the foreign key is the child table. and the other table is the reference or parent table.
Since i Can not see your tables, ill give you different example.
Look at the following two tables:
Persons table:
Personal_id LastName FirstName age
1 pretty bob 20
2 angry jack 30
3 happy sue 28
Order Table:
OrderID OrderNumber Personal_id
1 77895 3
2 44678 3
3 22456 2
4 24562 1
Now look how Personal_id column in Orders table points to Personal_id in persons table.
The Personal_id in persons table is the primary key and the Personal_id in the orders table is the FOREIGN KEY.
now except linking how does foreign key help:
two general ways that i can think of:
1- foreign key is like a constrain that makes sure no action would destroy the links between tables
2- foreign key also acts as a constrain to stop invalid data from being inserted into the foreign key column, as it has to reference to the primary key column in the other table
code example in MySql:
CREATE TABLE Orders (
OrderID int NOT NULL,
OrderNumber int NOT NULL,
PersonID int,
PRIMARY KEY (OrderID),
FOREIGN KEY (Personal_id) REFERENCES Persons(Personal_id)
);
code example is SQL-Server/MS Access/ Oracle:
CREATE TABLE Orders (
OrderID int NOT NULL PRIMARY KEY,
OrderNumber int NOT NULL,
PersonID int FOREIGN KEY REFERENCES Persons(Personal_id)
);
Primary key of Orders table is the orderID.
Foreign key of Orders table is what links it to persons table.
Personal_id columns are the columns that link both tables.
Both of the code chunks do the same depends what are you working with.
real world example:
assuming:
customer_Table column to be a primary key in restaurant table and foreign key in orders table.
if a waiter is putting customer_Table number 20 in the machine, and he puts customer_Table 200 by mistake such key does not exist as a primary key in restaurant table so he cant.
Extra:
what if you want to allow naming of the FOREIGN KEY constraint, and define a FOREIGN KEY constraint on many columns?
MySQL / SQL Server / Oracle / MS Access:
CREATE TABLE Orders (
OrderID int NOT NULL,
OrderNumber int NOT NULL,
Personal_id int,
PRIMARY KEY (OrderID),
CONSTRAINT FK_PersonOrder FOREIGN KEY (Personal_id)
REFERENCES Persons(Personal_id)
);
I'm creating a database that has to manage the orders of a food delivery company (for a school project). I created a menu table which naturally has to contain several dishes (starter, main course and a desert) and I also have a dish table. so the menu has to contain three foreign keys which reference the primary key of the dish table. But I get an error due to foreign key constraints every time I try to execute my script
here's the code for the tables (sorry, but there's an issue with inserting the code into the case)
create table plat(
id_plat integer primary key,
gluten boolean,
végétarien boolean,
nom varchar(30),
catégorie varchar(30)
);
create table menu(
id_menu integer primary,
entrée integer,
plat integer,
dessert integer,
foreign key(entrée) references plat(id_menu),
foreign key(plat) references plat(id_menu),
foreign key(dessert) references plat(id_menu)
);
after I execute my code using show ENGINE INNODB STATUS I get this error:
2016-12-29 21:42:58 7f2116e5c700 Error in foreign key constraint of table PROJET/menu:
there is no index in referenced table which would contain
the columns as the first columns, or the data types in the
referenced table do not match the ones in table.
Constraint:
CONSTRAINT "menu_ibfk_1" FOREIGN KEY ("entrée") REFERENCES "plat" ("id_menu")
The index in the foreign key in table is "entrée"
See http://dev.mysql.com/doc/refman/5.6/en/innodb-foreign-key-constraints.html
for correct foreign key definition.
Your foreign keys definitions are not correct, you try to link entree field from menu table with id_menu field from plat table. Try this way:
foreign key(entrée) references plat(id_plat)
Official docs
I am relatively new to the database world so bear with me. I'm just trying to add foreign key constraints and I keep getting error 1215 "cannot add foreign key constraint".
CREATE TABLE InProcessSamples
(
SampleNumber Int(6),
WorkOrder Int(8),
DueDate Date,
BeginsTesting Date,
FinishedTesting Date,
CONSTRAINT fk_sample_number FOREIGN KEY(SampleNumber) REFERENCES AllRecords(SampleNumber),
CONSTRAINT fk_work_order FOREIGN KEY(WorkOrder) REFERENCES SamplesReceived(WorkOrder)
);
CREATE TABLE SamplesReceived
(
WorkOrder Int(8) PRIMARY KEY,
SampleNumber Int(6),
RecTimeStamp DateTime,
PartNumber Int(10),
Description Char(36),
CONSTRAINT fk_sample_number FOREIGN KEY(SampleNumber) REFERENCES AllRecords(SampleNumber),
CONSTRAINT fk_part_number FOREIGN KEY(PartNumber) REFERENCES PartNumbers(PartNumber)
);
CREATE TABLE AllRecords
(
SampleNumber Int(6) PRIMARY KEY,
WorkOrder Int(8),
DueDate Date,
BeginsTesting Date,
FinishedTesting Date,
RecTimeStamp DateTime,
MeasurementOne Double,
MeasurementTwo Double,
PassDielectric Char(3),
PassedAllTest Char(3),
CONSTRAINT fk_work_order FOREIGN KEY(WorkOrder) REFERENCES SamplesReceived(WorkOrder),
CONSTRAINT fk_part_number FOREIGN KEY(PartNumber) REFERENCES PartNumbers(PartNumber)
);
CREATE TABLE PartNumbers
(
PartNumber Int(10) PRIMARY KEY,
Description Char(36)
);
Regardless of whether your design is off or not, you can't declare a foreign key reference to a table you haven't created yet.
CREATE TABLE statements are evaluated in order from top to bottom of your SQL script. As MySQL is trying to create the first table, the second and third tables don't exist yet. So there's nothing for the foreign keys to reference.
You should create tables in an order that allows the referenced table to exist before you create the table that has the foreign key to reference it. In this case, you have a circular dependency, so the only way to do it is to create either SamplesReceived or AllRecords without one of its foreign keys, and then go back afterward and add that foreign key.
CREATE TABLE PartNumbers, because it's needed by SamplesReceived and AllRecords
CREATE TABLE SamplesReceived, because it's needed by InProcessSamples and AllRecords
CREATE TABLE AllRecords, because it's needed by InProcessSamples
ALTER TABLE SamplesReceived ADD FOREIGN KEY(SampleNumber) REFERENCES AllRecords(SampleNumber);
CREATE TABLE InProcessSamples
That's if the circular reference is really needed.
But as other folks have answered, perhaps your circular reference isn't really a good design.
The circular reference could be needed; what it does in your case is enforce that for every row in SamplesReceived, you must have a matching row in AllRecords, and vice-versa, every row in AllRecords must have a matching row in SamplesReceived.
I don't know why that's important in your application. It might be, but you haven't told us anything about the workflow you're trying to model so I can't tell.
the normalization is all wrong:
this one is good:
Part
---------------
Part_id
Description
then you have redundancies and other issues everywhere...
maybe start with this:
WorkOrder
-------------
workorder_id
Sample
----------
sample_id
workorder_id
part_id
Test
--------------
test_id
description
min_passing_value
max_passing_value
TestResult
---------------
testresult_id
test_id
description
result_value
test_date
sample_id
I have been trying to create a foregin key with nbrseats but I i get the error 1005 all the time.
CAn someone help me!?
create table theater (
name varchar(30) primary key,
nbrseats int not null
) ENGINE=INNODB;
create table reservation (
nbr integer auto_increment,
users_username varchar(30),
cinemashow_showdate date,
movies varchar(30),
nbrseats int not null,
primary key (nbr),
foreign key (nbrseats) references theater(nbrseats),
foreign key (users_username) REFERENCES users(username)
on delete cascade,
foreign key (cinemashow_showdate, movies) references cinemashow(showdate, movie_title)
on delete cascade
) ENGINE=INNODB;
In order to be a FOREIGN KEY in another table, you must have an index created on theater.nbrseats. And in order to be able to reference a specific row reliably, it should therefore be a UNIQUE index. Otherwise, if you have duplicate values, the referencing table won't be able to discern which row it references. Even though InnoDB will allow you to create the relationship on a non-unique index, it is likely not the behavior you are looking for.
See this question for more info on that bit.
create table theater (
name varchar(30) primary key,
nbrseats int not null,
UNIQUE INDEX `idx_nbrseats` (nbrseats)
) ENGINE=INNODB;
The same will be true of the other FOREIGN KEY definitions in your table reservation, though we do not see their referenced tables posted here. The rules are:
The referenced column must be indexed (independently of any other compound indexes on it)
The referencing column must have exactly the same data type.
This kind of calls into question your design, however. If you are attaching a number of seats to a reservation, will the reservation number of seats exactly match the number available in the theater? Also this means that you could not have 2 theaters with the same number of seats.
You may need to reconsider your design here, and perhaps create a FOREIGN KEY that references theater.name instead of theater.nbrseats.