I've been trying to get a delete to cascade and it just doesn't seem to work. I'm sure I am missing something obvious, can anyone help me find it?
I would expect a delete on the 'articles' table to trigger a delete on the corresponding rows in the 'article_section_lt' table.
CREATE TABLE articles (
id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT,
url_stub VARCHAR(255) NOT NULL UNIQUE,
h1 VARCHAR(60) NOT NULL UNIQUE,
title VARCHAR(60) NOT NULL,
description VARCHAR(150) NOT NULL,
summary VARCHAR(150) NOT NULL DEFAULT "",
html_content TEXT,
date DATE NOT NULL,
updated TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
)ENGINE=INNODB;
CREATE TABLE article_sections (
/* blog, news etc */
id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT,
url_stub VARCHAR(255) NOT NULL UNIQUE,
h1 VARCHAR(60) NOT NULL,
title VARCHAR(60) NOT NULL,
description VARCHAR(150) NOT NULL,
summary VARCHAR(150) NOT NULL DEFAULT "",
html_content TEXT NOT NULL DEFAULT ""
)ENGINE=INNODB;
CREATE TABLE article_section_lt (
fk_article_id INTEGER UNSIGNED NOT NULL REFERENCES articles(id) ON DELETE CASCADE,
fk_article_section_id INTEGER UNSIGNED NOT NULL
)ENGINE=INNODB;
You need to explicitly declare the foreign key constraint. The REFERENCES clause on a column definition doesn't work.
Try this:
CREATE TABLE article_section_lt (
fk_article_id INTEGER UNSIGNED NOT NULL,
fk_article_section_id INTEGER UNSIGNED NOT NULL,
KEY fk_article_id (fk_article_id),
CONSTRAINT fk_article_section_lt_to_article FOREIGN KEY (fk_article_id) REFERENCES articles(id) ON DELETE CASCADE
)ENGINE=INNODB;
Related
create database [PostaShpejte]
use PostaShpejte
create table Posta
(
ID_Posta int not null Primary Key,
Emri varchar(50)not null,
Qyteti varchar(15) not null,
)
create table Dergesa
(
ID_Dergesa int IDENTITY(1,1) not null Primary Key,
Emri_Dergeses varchar(30) not null,
Pershkrimi varchar(100),
Qmimi int not null,
Statusi varchar(30) not null,
CONSTRAINT CHK_Statusi CHECK (Statusi='E regjistruar' or Statusi='E nisur' or Statusi='Ne depo' or Statusi='E refuzuar' or Statusi='E derguar'),
)
create table Menaxhon
(
ID_Dergesa int not null references Dergesa (ID_Dergesa),
ID_Posta int not null references Posta(ID_Posta),
Primary Key(ID_Dergesa,ID_Posta),
)
--drop table TelBleresi
create table TelBleresi
(
ID_Tel_Bleresi int not null,
--ID_Bleresi int not null,
NumriTel int not null Unique,
Primary Key(ID_Tel_Bleresi),
)
--drop table Bleresi
create table Bleresi
(
ID_Bleresi int not null,
ID_Tel_Bleresi int not null,
Emri varchar(20) not null,
Mbiemri varchar(20) not null,
Shteti varchar(20) not null,
Qyteti varchar(20) not null,
Rruga varchar(50) not null,
ZIPKodi int not null,
FOREIGN KEY(ID_Tel_Bleresi) references TelBleresi(ID_Tel_Bleresi),
Primary Key (ID_Bleresi , ID_Tel_Bleresi),
)
create table Dergohet
(
ID_Dergesa int not null,
ID_Bleresi int not null,
Data_e_regj date not null,
Data_e_mbrritjes date not null,
----------------PROBLEM HERE---------------------------
FOREIGN KEY (ID_Dergesa) references Dergesa(ID_Dergesa),
FOREIGN KEY (ID_Bleresi) references **Bleresi**(ID_Bleresi),
*Error: There are no primary or candidate key to table Bleresi ....*
---------------------------------------------------------
PRIMARY KEY (ID_Dergesa,ID_Bleresi),
)
Bleresi has a compound primary key (ID_Bleresi, ID_Tel_Bleresi), so you need to reference all columns. That means adding ID_Tel_Bleresi to Dergohet.
create table Dergohet(
ID_Dergesa int not null,
ID_Bleresi int not null,
ID_Tel_Bleresi int not null, -- add this column
Data_e_regj date not null,
Data_e_mbrritjes date not null,
FOREIGN KEY (ID_Dergesa) references Dergesa(ID_Dergesa),
-- Reference the full compound key
FOREIGN KEY (ID_Bleresi, ID_Tel_Bleresi) references Bleresi(ID_Bleresi, ID_Tel_Bleresi),
PRIMARY KEY (ID_Dergesa,ID_Bleresi),
)
While they have some uses, compound primary keys are annoying as they create a proliferation of foreign key columns and complicate indexing. Some of yours seem unnecessary: Bleresi already has a ID_Bleresi, is that not unique?
In general, I'd recommend using simple big integer (2 billion creeps up on you surprisingly fast) auto incrementing primary keys. If you need to guarantee other uniquenesses, make a unique index.
The error say that ID_Bleresi is not the primary key on Bleresi table and for that can't be a foreign key. The primary key is:
Primary Key (ID_Bleresi , ID_Tel_Bleresi)
If ID_Bleresi is not a unique column, I recommend that in the table, you create a new unique column that is the primary key. In case it is, it would be best to set ID_Bleresi as the unique primary key
I'm currently working through an assignment that is asking me to create a SQL database using SQL Server Express. This is what it's asking for:
CREATE DATABASE USING SQL
And this is the code I have tried running;
CREATE DATABASE db_Library
Go
USE db_Library
CREATE TABLE tbl_library_branch
(
library_branch_branch_id INT PRIMARY KEY NOT NULL IDENTITY (1,1),
library_branch_branch_name VARCHAR(50) NOT NULL,
library_branch_address VARCHAR(50) NOT NULL
);
CREATE TABLE tbl_publisher
(
library_publisher_publisher_name VARCHAR(50) PRIMARY KEY NOT NULL,
library_publisher_address VARCHAR(50) NOT NULL,
library_publisher_phone INT NOT NULL
);
CREATE TABLE tbl_books
(
library_books_book_id INT PRIMARY KEY NOT NULL IDENTITY (1,1),
library_books_title VARCHAR(50) NOT NULL,
library_books_publisher_name VARCHAR(50) NOT NULL CONSTRAINT fk_library_books_publisher_name FOREIGN KEY REFERENCES tbl_publisher(library_publisher_publisher_name) ON UPDATE CASCADE ON DELETE CASCADE
);
CREATE TABLE tbl_book_authors
(
library_book_authors_book_id INT NOT NULL CONSTRAINT fk_library_book_authors_book_id FOREIGN KEY REFERENCES tbl_books(library_books_book_id) ON UPDATE CASCADE ON DELETE CASCADE,
library_book_authors_author_name VARCHAR(50) NOT NULL
);
CREATE TABLE tbl_book_copies
(
library_book_copies_book_id INT NOT NULL CONSTRAINT fk_library_book_copies_book_id FOREIGN KEY REFERENCES tbl_books(library_books_title),
library_book_copies_branch_id INT NOT NULL,
library_book_copies_number_of_copies INT NOT NULL
);
CREATE TABLE tbl_book_loans
(
library_book_loans_book_id INT NOT NULL,
library_book_loans_branch_id INT NOT NULL,
library_book_loans_card_no INT NOT NULL,
library_book_loans_date_out INT NOT NULL,
library_book_loans_date_due INT NOT NULL
);
CREATE TABLE tbl_borrower
(
library_borrower_card_no INT PRIMARY KEY NOT NULL IDENTITY (1,1),
library_borrower_name VARCHAR(50) NOT NULL,
library_borrower_address VARCHAR(50) NOT NULL,
library_borrower_phone VARCHAR(50) NOT NULL
);
Using the library "Books" as an example it looks like I need to have BoodID as a primary key and Title as a primary key, but you can't have more than one primary key per table..
Then I have to take BookID from the Book_Copies table and the Book_Loans table connect to the primary key of Title in Books?
I'm beyond stuck at this point and would appreciate any resources you think could help.
There is no need to be so verbose. I think you want something more like this (for two tables):
CREATE TABLE tbl_publisher (
publisher_id int IDENTITY(1, 1) PRIMARY KEY,
publisher_name VARCHAR(50) NOT NULL UNIQUE,
address VARCHAR(50) NOT NULL,
phone INT NOT NULL
);
CREATE TABLE books (
book_id INT IDENTITY (1,1) PRIMARY KEY,
title VARCHAR(50) NOT NULL UNIQUE,
publisher_id INT NOT NULL CONSTRAINT fk_books_publisher__id FOREIGN KEY REFERENCES tbl_publisher(publisher_id) ON UPDATE CASCADE ON DELETE CASCADE
);
Notes:
Stick with synthetic primary keys for all the tables. That is, identity columns.
Other columns can be declared to be unique. That is fine.
I type quite fast. And yet I would quickly wary of typing library_book_ over and over. Such repetition just makes it harder to write and read queries.
create table Country(
code char(3) PRIMARY KEY,
name varchar2(100) NOT NULL
);
create table Member(
firstname varchar(100) NOT NULL,
lastname varchar(100) NOT NULL,
title varchar(100) NOT NULL,
member_id INTEGER PRIMARY KEY,
Country_code char(3) NOT NULL REFERENCES Country(code)
ON DELETE CASCADE
ON UPDATE CASCADE
);
create table Athlete(
id integer NOT NULL REFERENCES Member(member_id)
ON DELETE NO ACTION
ON UPDATE CASCADE
);
create table Official(
id integer NOT NULL REFERENCES Member(member_id)
ON DELETE NO ACTION
ON UPDATE CASCADE
);
create table Staff(
id integer NOT NULL REFERENCES Member(member_id)
ON DELETE NO ACTION
ON UPDATE CASCADE
);
Create table Books(
when timestamp NOT NULL,
member_id integer NOT NULL REFERENCES Member(member_id),
start_time timestamp NOT NULL REFERENCES Journey(start_time),
start_date date NOT NULL REFERENCES Journey(start_date),
byStaff integer NOT NULL REFERENCES Staff(id)
);
create table Journey(
start_time timestamp PRIMARY KEY,
start_date date PRIMARY KEY,
member_id integer PRIMARY KEY REFERENCES Member(member_id),
nbooked integer NOT NULL,
departure varchar(100) NOT NULL REFERENCES Place(name),
arrival varchar(100) NOT NULL REFERENCES Place(name),
code varchar(100) NOT NULL REFERENCES Vehicle(code)
);
create table Vehicle(
code varchar(100) PRIMARY KEY,
capacity varchar(100) NOT NULL
);
create table Place(
name varchar(50) PRIMARY KEY,
address varchar(100) NOT NULL,
longitude float NOT NULL,
latitude float` NOT NULL
);
create table SportVenue(
name varchar(50) NOT NULL REFERENCES Place(name)
);
create table Accommodation(
name varchar(50) NOT NULL REFERENCES Place(name)
);
create table Event(
name varchar(100) PRIMARY KEY,
result_type varchar(100) NOT NULL,
time timestamp NOT NULL,
date date NOT NULL,
sport_name varchar(50) NOT NULL REFERENCES Sport(name),
);
For the DDL above, is there any needs of adding constraints for the DDL? If it needs to be modified, which constraints should be implemented? I am so confused on writing DDL... wef ewf ew fwe fewf wef oiwejf oiwej fioejwo ifjewo ifwjeoif jewoiew fiowefioje w
Thanks.
Constraints aka validation should be implemented from all sides of your application. Front-end, back-end, and your database. Otherwise, you would fail on the overall data integrity. So, the answer to your question is yes. Details depend on the nature of the data you will be working with.
I have 2 SQL statement as follows:
CREATE TABLE IF NOT EXISTS countries
(
country_id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
country varchar(45) NOT NULL
);
CREATE TABLE IF NOT EXISTS patients
(
p_id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
p_fname varchar(50) NOT NULL,
p_mname varchar(10) NULL,
p_lname varchar(50) NOT NULL,
age INT NOT NULL,
sex SET ('Male','Female'),
phone_num_mobile varchar(10) NULL,
phone_num_res varchar(7) NULL,
phone_num_office varchar(7) NULL,
email varchar(75) NULL,
addr_house varchar(10) NULL,
addr_street1 varchar(45) NOT NULL,
addr_street2 varchar(45) NULL,
addr_street3 varchar(45) NULL,
addr_city varchar(20) NOT NULL,
addr_country varchar(45) NOT NULL,
occupation varchar(20) NOT NULL,
married BOOLEAN NOT NULL,
FOREIGN KEY(addr_country) REFERENCES countries(country)
);
The first one executes successfully and the second one, which assigns a foreign key to the previous table, fails to execute with the message 'Foreign key constraint incorrectly formed'. I have also tried altering the second query's foreign key field(addr_country) to have the same name as that of the 'countries' table(country) but it were top no avail.
Can anyone please explain me what's going on and suggest me with a solution to this problem?
Thanks in advance.
A foreign key in MariaDB can only reference either a primary key in another table or a unique key. In this case, the countries table already has a primary key, so you can create a unique key on the country column.
Try putting a unique constraint on the country column in the countries table:
CREATE TABLE IF NOT EXISTS countries
(
country_id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
country varchar(45) NOT NULL
UNIQUE KEY(country)
);
Late edit: As the commentors mentioned, you might want to just reference the country_id primary key instead of the country name. Since no two countries in the world have the same name, either might work in practice.
I'm trying to create a hypothetical videostore database and this error message comes up everytime I execute this query:
DROP DATABASE videostore
CREATE DATABASE videostore
CREATE TABLE genre
(
genre_id INT NOT NULL PRIMARY KEY IDENTITY,
genre_name VARCHAR(15) NOT NULL
);
CREATE TABLE classification
(
rating VARCHAR(2) NOT NULL CONSTRAINT classification_pk PRIMARY KEY,
description VARCHAR(100) NOT NULL,
minimum_age INT NULL,
);
CREATE TABLE format
(
format_id INT NOT NULL CONSTRAINT format_pk PRIMARY KEY IDENTITY,
format_name VARCHAR(8) NOT NULL,
purchase_cost FLOAT NOT NULL
);
CREATE TABLE rental_cost
(
rental_cost_id INT NOT NULL CONSTRAINT rental_cost_pk PRIMARY KEY IDENTITY,
rental_name VARCHAR(15) NOT NULL,
rental_cost FLOAT NOT NULL,
rental_days TINYINT NOT NULL
);
CREATE TABLE customer
(
customer_id INT NOT NULL CONSTRAINT customer_pk PRIMARY KEY IDENTITY,
first_name VARCHAR(20) NOT NULL,
surname VARCHAR(20) NOT NULL,
dob DATETIME NOT NULL,
home_address VARCHAR(50) NOT NULL,
contact_number VARCHAR(10) NOT NULL,
referrer_id INT NULL FOREIGN KEY REFERENCES customer(customer_id),
);
CREATE TABLE movie
(
movie_id INT NOT NULL CONSTRAINT movie_pk PRIMARY KEY IDENTITY,
movie_name VARCHAR(40) NOT NULL,
year SMALLINT NOT NULL,
duration SMALLINT NULL,
descrip VARCHAR(120) NULL,
classification VARCHAR(2) NOT NULL FOREIGN KEY REFERENCES classification(rating),
rental_cost_id INT NOT NULL FOREIGN KEY REFERENCES rental_cost(rental_cost_id),
);
CREATE TABLE copy
(
copy_id INT NOT NULL CONSTRAINT copy_pk PRIMARY KEY IDENTITY,
movie_id INT NOT NULL FOREIGN KEY REFERENCES movie(movie_id),
format_id INT NOT NULL FOREIGN KEY REFERENCES format(format_id),
);
CREATE TABLE rental
(
rental_id INT NOT NULL CONSTRAINT rental_pk PRIMARY KEY IDENTITY,
copy_id INT NOT NULL FOREIGN KEY REFERENCES copy(copy_id),
customer_id INT NOT NULL FOREIGN KEY REFERENCES customer(customer_id),
rental_date DATETIME NOT NULL,
return_date DATETIME NULL
);
CREATE TABLE genre_movie
(
genre_id INT NOT NULL FOREIGN KEY REFERENCES genre(genre_id),
movie_id INT NOT NULL FOREIGN KEY REFERENCES movie(movie_id),
CONSTRAINT genre_movie_pk PRIMARY KEY (genre_id, movie_id)
);
(Sorry it's not in the correct format for reading a script with ease, I just really couldn't work out how to do that.)
Basically when I execute the SQL script it tells me that the object 'genre' already exists, but I can't see it anywhere else in my code.
And the table shouldn't already exist because I drop the database each time the script is executed right?
Sidenote - if there's a better way to make it so the database is dropped only if it exists please help me with that also.
Appreciate it.
I think you need to add USE videostore after the CREATE DATABASE videostore. Otherwise you are creating tables in whatever database you are currently in.
I think you are executing this in the context of the master database. If you check it you will probably see all your tables are actually in master.
Change the first part to this:
DROP DATABASE videostore
CREATE DATABASE videostore
USE videostore
CREATE TABLE genre
It's generally best to execute sql statements when required - try:
DROP DATABASE videostore
GO
CREATE DATABASE videostore
GO
USE videostore
CREATE TABLE genre
(
genre_id INT NOT NULL PRIMARY KEY IDENTITY,
genre_name VARCHAR(15) NOT NULL
);
GO
etc.