Is it possible to have a primary key composed of foreign keys fk1, fk2, fk3
Where:
fk1 should never be null
fk2 and fk3 can be null
I have the following SQL:
CREATE TABLE role_mappings (
ROLE_NAME VARCHAR(64) NOT NULL,
NESTED_ROLE_NAME VARCHAR(64) DEFAULT NULL,
PRIVILEGE_NAME VARCHAR(64) DEFAULT NULL,
PRIMARY KEY (ROLE_NAME, NESTED_ROLE_NAME, PRIVILEGE_NAME),
CONSTRAINT fk_access_roles_rm_1 FOREIGN KEY (ROLE_NAME) REFERENCES access_roles (ROLE_NAME),
CONSTRAINT fk_access_privileges FOREIGN KEY (PRIVILEGE_NAME) REFERENCES access_privileges(PRIVILEGE_NAME),
CONSTRAINT fk_access_roles_rm_2 FOREIGN KEY (NESTED_ROLE_NAME) REFERENCES access_roles(ROLE_NAME)
);
When I insert NULL into NESTED_ROLE_NAME or PRIVILEGE_NAME, I get:
Column 'NESTED_ROLE_NAME' cannot accept a NULL value.
What's the proper way of doing this?
Primary key values must be unique. If you allow null values into these fields that makeup the primary key you will quickly run into trouble with non-uniqueness. AVOId using null values would be my advice.
Related
MER
I need help creating this MER in Oracle. Specifically in FOTOS table as I have this code:
CREATE TABLE "FOTOS"
(
"ID_FOTO" INT NOT NULL ENABLE,
"ID_USU" INT NOT NULL ENABLE,
"FECHA" DATE NOT NULL ENABLE,
CONSTRAINT "FOTOS_PK"
PRIMARY KEY ("ID_FOTO") ENABLE,
CONSTRAINT "FOTOS_FK"
FOREIGN KEY ("ID_USU") REFERENCES "USUARIOS" ("ID_USU") ENABLE
)
However I keep getting this error:
ORA-02270: no matching unique or primary key for this column-list
ID_USU is one of two primary keys in USUARIOS
USUARIOS TABLE
ID_USU is one of two primary keys in USUARIOS
No. A table can have just one primary key. It can have more than one unique key, but you can only make one of them primary.
What you mistakenly did instead is create a composite primary key. You want the ID to be unique and the name to be unique, but instead you made the combination of ID and name unique, thus allowing duplicate IDs and duplicate names in the table.
What you have:
create table usuarios
(
id_usu number not null,
nomusu varchar2(50) not null,
...
constraint pk_usuarios primary key (id_usu, nomusu)
);
What you want instead:
create table usuarios
(
id_usu number not null,
nomusu varchar2(50) not null,
...
constraint pk_usuarios primary key (id_usu),
constraint uq_usuarios_nomusu unique (nomusu)
);
Foreign keys have to match the primary/unique key they reference column for column. Since the primary key of "USUARIOS" are columns "ID_USU" and "NOMUSU" you need two columns to add FK from "FOTOS" to "USUARIOS", so just add "NOMUSU" column to "FOTOS" and write:
CREATE TABLE "FOTOS"
(
"ID_FOTO" INT NOT NULL ENABLE,
"ID_USU" INT NOT NULL ENABLE,
"NOMUSU" VARCHAR2(50) NOT NULL ENABLE,
"FECHA" DATE NOT NULL ENABLE,
CONSTRAINT "FOTOS_PK"
PRIMARY KEY ("ID_FOTO") ENABLE,
CONSTRAINT "FOTOS_FK"
FOREIGN KEY ("ID_USU","NOMUSU") REFERENCES "USUARIOS" ("ID_USU","NOMUSU") ENABLE);
CREATE TABLE location (
uid int not null auto_increment primary key,
name varchar(255) NOT NULL,
`state_uid` int not null,
FOREIGN KEY location(state_uid)
REFERENCES state(uid)
ON UPDATE CASCADE
ON DELETE RESTRICT,
`city_uid` int not null,
FOREIGN KEY location(city_uid)
REFERENCES city(uid)
ON UPDATE CASCADE
ON DELETE RESTRICT,
`area_uid` int not null,
FOREIGN KEY location(area_uid)
REFERENCES area(uid)
ON UPDATE CASCADE
ON DELETE RESTRICT
);
CREATE TABLE location (
uid int not null auto_increment primary key,
name varchar(255) NOT NULL,
state_uid int not null,
city_uid int not null,
area_uid int not null,
CONSTRAINT fk_state FOREIGN KEY (state_uid) REFERENCES state(uid) ,
CONSTRAINT fk_city FOREIGN KEY (city_uid) REFERENCES city(uid) ,
CONSTRAINT fk_area FOREIGN KEY (area_uid) REFERENCES area(uid)
);
Try this query
make sure parent tables exists
Your version is almost just fine. The problem is the location in the foreign key reference.
You have no issue with the cascading stuff or the ordering of the columns. So, this works:
CREATE TABLE location (
uid int not null auto_increment primary key,
name varchar(255) NOT NULL,
`state_uid` int not null,
FOREIGN KEY (state_uid) REFERENCES state(uid) ON UPDATE CASCADE ON DELETE RESTRICT,
`city_uid` int not null,
FOREIGN KEY (city_uid) REFERENCES city(uid) ON UPDATE CASCADE ON DELETE RESTRICT,
`area_uid` int not null,
FOREIGN KEY (area_uid) REFERENCES area(uid) ON UPDATE CASCADE ON DELETE RESTRICT
);
Here is a SQL Fiddle.
Note that it is often traditional to put explicit foreign key (and other constraints) after the column definitions, there is no rule or standard for this. In fact, most databases support in-line foreign key definitions. MySQL does not, however.
I have the following queries that I run to create tables in MS SQL Server:
CREATE TABLE menus
(
menu_id int NOT NULL PRIMARY KEY,
menu_name char,
other_details char
)
CREATE TABLE bookings
(
booking_Id int NOT NULL PRIMARY KEY,
date_booked DATE,
date_of_booking DATE,
other_details char,
staff_id int FOREIGN KEY REFERENCES staff(staff_id),
customer_id int FOREIGN KEY REFERENCES customers(customer_id)
)
CREATE TABLE menus_booked
(
menu_id INT NOT NULL,
booking_id INT NOT NULL,
CONSTRAINT PK_menus_booked PRIMARY KEY(menu_id,booking_id),
FOREIGN KEY (menu_id) REFERENCES menus(menu_id),
FOREIGN KEY (booking_id) REFERENCES bookings(booking_id)
)
CREATE TABLE menu_changes
(
change_id int NOT NULL PRIMARY KEY,
menu_id int NOT NULL,
booking_id int NOT NULL,
change_details char,
FOREIGN KEY (menu_id) REFERENCES menus_booked(menu_id),
FOREIGN KEY (booking_id) REFERENCES menus_booked(booking_id)
)
On running the last query I get the error:
There are no primary or candidate keys in the referenced table 'menus_booked' that match the referencing column list in the foreign key 'FK_menu_chan_menu'
I am unsure if my queries are correct and can't resolve this error.
The primary key of menus_booked is a unique combination of menu_id and booking_id. A foreign must point to that combination, not just one of its fields, which is not necessarily unique. Your query currently tries to define two foreign keys, one on each column, instead of one foreign key on the combination of the columns:
CREATE TABLE menu_changes
(
change_id int NOT NULL PRIMARY KEY,
menu_id int NOT NULL,
booking_id int NOT NULL,
change_details char,
FOREIGN KEY (menu_id, booking_id)
REFERENCES menus_booked(menu_id, booking_id) -- Here!
)
A foreign key has to reference a primary key (or unique key but here the PK is the problem), and it has to reference it in it's entirety.
FOREIGN KEY (menu_id) REFERENCES menus_booked(menu_id),
FOREIGN KEY (booking_id) REFERENCES menus_booked(booking_id)
You have two foreign key's referencing part of the primary key of menus_booked. You'll have to alter it to:
FOREIGN KEY (menu_id, booking_id) REFERENCES menus_booked(menu_id, booking_id)
I'm getting this error when trying to create a table with foreign key:
There are no primary or candidate keys in the referenced table 'TeamToPlayers' that match the referencing column list in the foreign key 'FKey2'.
I don't understand why, there is a primary key in the table TeamToPlayers.
Here are the queries:
create table TeamToPlayers
(TeamName varchar(50) NOT NULL,
PlayerName varchar(50) NOT NULL,
primary key(TeamName,PlayerName),
CONSTRAINT FKey FOREIGN KEY (TeamName) REFERENCES Teams(TeamName)
)
create table Players
(PlayerName varchar(50) NOT NULL,
primary key(PlayerName),
CONSTRAINT FKey2 FOREIGN KEY (PlayerName) REFERENCES TeamToPlayers(PlayerName)
);
Table TeamToPlayers primary key consists of two fields - you must reference both as otherwise it's not a key. I think you may have your key the wrong way round - it should be on TeamToPlayers and referencing Players like so:
create table TeamToPlayers
(
TeamName varchar(50) NOT NULL,
PlayerName varchar(50) NOT NULL,
primary key(TeamName,PlayerName),
CONSTRAINT FKey FOREIGN KEY (TeamName) REFERENCES Teams(TeamName),
CONSTRAINT FKey2 FOREIGN KEY (PlayerName) REFERENCES Players(PlayerName)
)
create table Players
(PlayerName varchar(50) NOT NULL,
primary key(PlayerName),
);
Unable to create table as oracle shows ' no matching unique or primary key for this column-list' when I did label the primary key reference for the required table.
First table created successfully:
CREATE TABLE TEST
(
TESTno VARCHAR2(6) NOT NULL,
ExamNo VARCHAR2(6) NOT NULL,
TEST_Date DATE NOT NULL,
ACTUAL DATE,
PREDICTED Date,
CONSTRAINT TESTPKs PRIMARY KEY (TEST_Date, TESTno, ExamNo),
CONSTRAINT TTESTNO_Fk FOREIGN KEY (TESTno) REFERENCES TESTPAPER (Flightno)
CONSTRAINT TEXAMNo_FK FOREIGN KEY (ExamNo) REFERENCES Exam (ExamNo)
);
Here's the table i want to create and gives me error:
CREATE TABLE Assignment
(
TEST_Date DATE NOT NULL,
ExamNo VARCHAR2(6) NOT NULL,
TestNo VARCHAR2(6) NOT NULL,
Type VARCHAR2(20),
Hours_Spent Decimal(4,2),
CONSTRAINT ASSIGNPKS PRIMARY KEY (TEST_Date, TestNo , ExamNo),
CONSTRAINT ASSIGNTESTDATE_FK FOREIGN KEY (TEST_Date) REFERENCES TEST(TEST_Date) ON
DELETE CASCADE,
CONSTRAINT ASSIGNTESTNO_FK FOREIGN KEY (TESTno) REFERENCES TESTPAPER (Flightno)
CONSTRAINT TEXAMNo_FK FOREIGN KEY (ExamNo) REFERENCES Exam (ExamNo)
);
May i know where's the issue that it keeps giving me no matching unique primary keys? I already tried to recreate and labelled the 'test_Date' as my primary key. But oracle can't seems to find.
Thanks
The PK you refer to is PRIMARY KEY (TEST_Date, TESTno, ExamNo) — hence the foreign key should be FOREIGN KEY (TEST_Date, TESTno, ExamNo) as well. The error you're getting is due to your attempt to refer to a part of TEST's PK.
See also http://download.oracle.com/docs/cd/B10500_01/server.920/a96524/c22integ.htm
Check the tables you are referencing in your foreign keys. Those columns must be the primary key or otherwise unique on the foreign table.