Question

2. Write a script that implements the following design: In the Downloads table, the user_id and product_id columns are the foreign keys. Create these tables in the ex schema. Create the sequences for the user_id, download_id, and product_id columns. Include a PL/SQL script to drop the table or sequence if it already exists. Include any indexes that you think are necessary. 3. Write a script that adds rows to the database that you created in exercise 2. Add two rows to the Users and Products tables. Add three rows to the Downloads table: one row for user 1 and product 2; one row for user 2 and product 1; and one row for user 2 and product 2. Use the SYSDATE function to insert the current date into the download_date column. Use the sequences created in the previous exercise to get the values for the user_id, download_id, and product_id columns. Write a SELECT statement that joins the three tables and retrieves the data from these tables like this: Sort the results by the email address in descending sequence and the product name in ascending sequence. 4. Write an ALTER TABLE statement that adds two new columns to the Products table created in exercise 2. Add one column for product price that provides for three digits to the left of the decimal point and two to the right. This column should have a default value of 9.99. Add one column for the date and time that the product was added to the database. 5. Write an ALTER TABLE statement that modifies the Users table created in exercise 2 so the first_name column can store NULL values and can store a maximum of 20 characters. Code an UPDATE statement that inserts a NULL value into this column. It should work since this column now allows NULL values. Code another UPDATE statement that attempts to insert a first name that’s longer than 20 characters. It should fail due to the length of the column.

Answer 1

GO create TABLE user user_id int Primary key NOT NULL email address varchar (20), first name varchar (20), last name varchar (20) )i create table downloads download_id int Primary key NOT NULL user_id int, download date date, filename varchar (20), product_id int, CONSTRAINT fk_column FOREIGN KEY (user_id) REFERENCES user (user_id) FOREIGN KEY (product_id) REFERENCES products (product_id) E create table products (

declare var_count int; select count (*) INTO var count from all tables where OWNER -BATCH] and table_name "users"; from all tables where OWNER -BATCH] and table_name"downloads" from all-tables where OMER = [BATCH] and table-name = "products"; if var count > 0 then begin drop table user: drop table downloads; drop table products; end