I am encountering a problem for my database.

Here is the relationships of the database

And tried to do the query for how many transactions have movie "Harry_Potter"?

so I used SQL query:

SELECT
COUNT(td.movie) AS number_of_occurrence,
td.transaction_number
FROM
TransactionDetails td,
MovieDetails md
WHERE
md.movie = Harry_Potter

But it asks for Harry_Potter enter parameter value why? The relevant SQL statements are

CREATE TABLE TransactionDetails 
(
transaction_number INTEGER PRIMARY KEY,
movie VARCHAR(30) NOT NULL,
date_of_transaction DATE NOT NULL,
member_number INTEGER NOT NULL
)

CREATE TABLE MovieDetails
(
movie VARCHAR(30) PRIMARY KEY,
movie_type VARCHAR(3) NOT NULL,
movie_genre VARCHAR(10) NOT NULL
)

ALTER TABLE TransactionDetails
ADD CONSTRAINT member_number_fk FOREIGN KEY (member_number) REFERENCES    LimelightMemberDetails(member_number);

ALTER TABLE TransactionDetails
ADD CONSTRAINT transaction_number_drink_fk FOREIGN KEY (transaction_number) REFERENCES DrinkTransactionDetails(transaction_number);

ALTER TABLE TransactionDetails
ADD CONSTRAINT transaction_number_food_fk FOREIGN KEY (transaction_number) REFERENCES FoodTransactionDetails(transaction_number);

ALTER TABLE TransactionDetails
ADD CONSTRAINT movie_fk FOREIGN KEY (movie) REFERENCES MovieDetails (movie);

Thank you for your help! If there is anything wrong with my database design please let me know! thank you!