I want to create two tables, one is having primary key and other for foreign key.
So my requirement is the values in users should be available which are present only in customers table other vice show error constraint violation.
Did something like this, but still am able to insert values in users which are not in customers.
create table if not exists customers
(
cust_user_id int,
primary key (cust_user_id)
);
create table if not exists users
( prid INT,
foreign key (prid) references customers(cust_user_id) ON UPDATE CASCADE
);
Any suggestion ?
Thanks
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.
Misson:
I'm trying to create two tables in MySQL, the first table has two primary keys (composite). The second table has three, two of which are foreign keys that reference the first tables two primary keys. So now I'm trying to bridge them, which isolates the problem code and can be seen below.
Issue:
MySQL workbench refuses allow me to create a table that references another table's two primary keys. It just gives me the error code: 1215. Cannot add foreign key constraint.
I tried:
Changing the attribute types from datetime to varchar(). Changing the attribute names. Checked spelling 5 times. Referencing only one key works fine, but I need both.
Problem Code (SQL Table):
CREATE TABLE IF NOT EXISTS TestInformation2
(
WorkOrder varchar(15),
Date datetime,
TechnicianID smallint,
Primary key (WorkOrder, Date)
) ENGINE = InnoDB;
CREATE TABLE IF NOT EXISTS TestBridge2
(
TestBridgeID integer Primary key,
WorkOrder varchar(15),
Date datetime,
Foreign key (WorkOrder) references TestInformation (WorkOrder),
Foreign key (Date) references TestInformation (Date)
) ENGINE = InnoDB;
Result I want:
Create the table 'TestBridge' which has the two foreign key attributes: WorkOrder and Date
It should be one composite foreign key, not two:
CREATE TABLE `TestBridge2` (
`TestBridgeID` INTEGER NOT NULL,
`WorkOrder` VARCHAR(15),
`Date` DATETIME,
PRIMARY KEY (`TestBridgeID`),
CONSTRAINT FOREIGN KEY (`WorkOrder`, `Date`) REFERENCES `TestInformation2` (`WorkOrder`, `Date`)
)
ENGINE=InnoDB;
One single foreign key has to be created for this like:
CREATE TABLE IF NOT EXISTS TestBridge2
(
TestBridgeID integer Primary key,
WorkOrder varchar(15),
Date datetime,
Foreign key (WorkOrder, Date) references TestInformation2 (WorkOrder, Date)
) ENGINE = InnoDB;
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 have 2 tables here for example table A and table B, how can i insert data when both of the tables consist of foreign key of each other? like table A got an attribute is foreign key references of table B, and table B got an attribute is foreign key references of table A
create table abc
(ID varchar(10),
subID varchar(10),
primary key (ID),
foreign key (subID) references def(SubID)
)
create table def
(SubID varchar(10),
ID varchar(10),
primary key (SubID),
foreign key (ID) references abc(ID)
)
somehow like this(i skipped other various informations)
I don't think it will be possible in your current design.
If you really have the need to do insert with cross dependency over the two tables, remove the one foreign key. Then you can do an insert on table ABC and then DEF.
I also think your DB design is incorrect.
I have a table articles and I want to create another table summaries that is a child of articles table.
I've used the following sql to create summaries table but however mysql keeps throwing an error #1072 - Key column 'article_id' doesn't exist in table
CREATE TABLE summaries(
summary_id INT NOT NULL AUTO_INCREMENT,
summary TEXT,
PRIMARY KEY ( summary_id),
FOREIGN KEY (article_id) REFERENCES articles(article_id)
)ENGINE=INNODB;
you dont have article_id in your table summaries, you may mean this:
FOREIGN KEY (summary_id) REFERENCES articles(article_id)
if you want make summary_id as foreign key to article_id in articles table.
But make sure they have same structure properties.
EDIT:
or create a column article_id in summaries table and make it foreign key
CREATE TABLE summaries(
summary_id INT NOT NULL AUTO_INCREMENT,
summary TEXT,
article_id INT,
PRIMARY KEY ( summary_id),
FOREIGN KEY (article_id) REFERENCES articles(article_id)
)ENGINE=INNODB;
EDIt:
INSERT INTO `summaries` (summary,article_id)
VALUES ($yoursummryVar , (SELECT article_id
FROM articles
WHERE ........)
)
i didnt test it.