mysql 存储过程判断重复的不插入数据

delimiter $$
create procedure proc_add_book(in $bookName varchar(200),in $price float)
begin
  declare $existsFlag int default 0;
  select bookId into $existsFlag from book where bookName = $bookName limit 1;
  if bookId > 0 then
  #if not exists (select  from book where bookNumber = $bookName) then
    insert into book(bookNumber,price) values($bookName,$price);
  end if;
end$$
delimiter ;