How to write 3 SQL queries (pure, not checks in the code)?

Question

SQL

There are two tables:

CREATE TABLE `books` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`author_id` INT(11) NOT NULL,
`title` VARCHAR(255) NOT NULL,
`price` FLOAT NOT NULL,
PRIMARY KEY (`id`),
INDEX `fk_author_id` (`author_id`),
CONSTRAINT `fk_author_id` FOREIGN KEY (`author_id`) REFERENCES `authors` (`id`) ON UPDATE CASCADE ON DELETE CASCADE
)

CREATE TABLE `authors` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) NOT NULL,
PRIMARY KEY (`id`)
)

It is required to write 3 SQL queries (pure, not by checks in the code):

1. Display all books and their authors.
2. Find authors who don't have any books.
3. Find authors who have more than one book.

I only know basic SQL stuff. Can anyone explain on the fingers what needs to be done to solve this and what topics of the documentation need to be studied for this?

Answer 1

select `authors`.`name`, `books`.`title`
  from `books`
  left join `authors` ON `authors`.`id` = `books`.`author_id`

select `authors`.`name`, count(`books`.`id`) as cnt
  from `books`, `authors`
  group by `books`.`author_id`
  having count(`books`.`id`) = 0

select `authors`.`name`, count(`books`.`id`) as cnt
  from `books`, `authors`
  group by `books`.`author_id`
  having count(`books`.`id`) > 1