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create table author (author_id integer primary key,
authorName varchar(30),
email varchar (25), gender varchar (6));
create table book (BookId integer not null unique,
ISBN integer primary key,
book_name varchar (30) not null,
author integer, ed_num integer,
price integer, pages integer,
foreign key (author) references author (author_id) on delete cascade);
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ALTER TABLE sounds ADD COLUMN sounds INT NOT NULL,
ADD FOREIGN KEY (sounds) REFERENCES characters(character_id);
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ALTER TABLE message ADD FOREIGN KEY (sender) REFERENCES users;
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ALTER TABLE message ADD FOREIGN KEY (sender) REFERENCES users;
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ALTER TABLE Evaluation
ADD CONSTRAINT FK_Evaluation_CodeEpreuve
FOREIGN KEY (CodeEpreuve) REFERENCES YourReferencedTable(ReferencedColumn);
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ALTER TABLE message ADD FOREIGN KEY (sender) REFERENCES users;