Errors in my schema creation script - sql

Question

So I have a simple SQL script which creates a database schema of a simple library online catalog:
DROP TABLE book_copies;
/
DROP TABLE books_authors_xref;
/
DROP TABLE authors;
/
DROP TABLE books;
/
CREATE TABLE books (
isbn VARCHAR2(13) NOT NULL PRIMARY KEY,
title VARCHAR2(200),
summary VARCHAR2(2000),
date_published DATE,
page_count NUMBER
);
/
CREATE TABLE authors (
name VARCHAR2(200) NOT NULL PRIMARY KEY
);
/
CREATE TABLE books_authors_xref (
author_name VARCHAR2(200),
book_isbn VARCHAR2(13),
CONSTRAINT pk_books_authors_xref PRIMARY KEY (author_name, book_isbn),
CONSTRAINT fk_books_authors_xref1 FOREIGN KEY (author_name) REFERENCES authors (name),
CONSTRAINT fk_books_authors_xref2 FOREIGN KEY (book_isbn) REFERENCES books (isbn)
);
/
CREATE TABLE book_copies (
barcode_id VARCHAR2(100) NOT NULL PRIMARY KEY,
book_isbn VARCHAR2(13),
CONSTRAINT fk_book_copies FOREIGN KEY (book_isbn) REFERENCES books (isbn)
);
/
Whenever I run it through SQL*Plus, I get many errors during its execution even though it looks like all SQL orders execute properly. This is the output I get:
What does that mean? Am I doing something wrong?

Answer 1

The / in SQL*Plus executes the "command in the buffer". A statement terminated with a semicolon is executed and put into the buffer.
So the CREATE TABLE books .... is actually run twice. The first time because of the semicolon ; (which puts the statement into the buffer) and the second time when the parser hits the /.
That's why you get the "name is already used" error.
So you need to use either a semicolon or a slash, but not both.
Edit
You can see what's going on, when manually running a statement using both, in the following log I copied & pasted the first statement from your script to a SQL*Plus console:
SQL> DROP TABLE book_copies;
Table dropped.
SQL> /
DROP TABLE book_copies
*
ERROR at line 1:
ORA-00942: table or view does not exist
You can see clearly how the DROP TABLE is execute because of the semicolon, and how the / executes it again.