how to verify in mysql if the number of rented books is lass 1

Completely untested, but should point you in the right general direction...

// Connect to database.

Connection C = DriverManager.getConnection("jdbc:mysql://host/database_name","username","password");

// Prepare SQL statement to select details of requested book (by book_id?).

PreparedStatement PStmt = C.prepareStatement("SELECT book_id, book_name, book_count FROM books where book_id=?");

// Requested book id...:)

int requestedBookId = 20;

// Set placeholder value for book id.

PStmt.setInt(1, requestedBookId);

// Execute...

ResultSet RS = PStmt.executeQuery();

// Get record...

RS.first();

// Is the current book count greater than 0...

if ( RS.getInt("book_count") > 0 )

{

// Do whatever with the "client" and "rent" databases

// (did you mean "client" and "rent" tables?)

}

// Close all

PStmt.close();

RS.close();

C.close();

beetle_buma at 2007-7-12 1:46:48 >

Thanks for the ideea!

And one question: you know i have the 3 tables : books,clients,and rent!how can i do that if somebody rents a book than automaticaly the number of the rented book in the book table substracts with one, i mean nr_book = nr_book -1.

Can somebody help me!

thanks to all

Killer86a at 2007-7-12 1:46:48 >

You haven't supplied the id of the specific book you're trying to update...

UPDATE book,client,rent SET

nrbook = nrebook-1

WHERE book.idbook=rent.idbooki AND

client.idclient=rent.idclient AND

book.idbook=?

... see use of placeholder "?" as posted earlier.

Gotta say I'm not entirely clear on why you need to join to the "client" and "rent" tables to reduce an available count (ie nrebook) in the "book" table which you already know the id of.

beetle_buma at 2007-7-12 1:46:48 >