Many-to-many interview question

queries.sql

-- select all query --

SELECT b.bookTitle, a.authorName FROM book b 
INNER JOIN author_book ab ON ab.bookID = b.bookID
INNER JOIN author a ON a.authorID = ab.authorID
ORDER BY b.bookTitle

-- select all with authors concantenated --

SELECT b.bookTitle, GROUP_CONCAT(a.authorName) authors FROM book b
INNER JOIN author_book ab ON (ab.bookID = b.bookID)
INNER JOIN author a ON (ab.authorID = a.authorID)
GROUP BY b.bookID

-- select books written by 2 authors only --

SELECT b.bookTitle FROM author_book ab
INNER JOIN book b ON ab.bookID = b.bookID
GROUP BY ab.bookID HAVING COUNT(1) = 2

-- select books written by exact 2 authors -- 

SELECT b.bookTitle FROM book b
INNER JOIN (
    SELECT ab.bookID FROM author_book ab 
    WHERE ab.bookID IN (
        SELECT ab.bookID FROM author_book ab
        INNER JOIN author a ON a.authorID = ab.authorID
        GROUP BY ab.bookID HAVING COUNT(1) = 2
    ) AND ab.authorID IN (
        SELECT a.authorID FROM author a 
        WHERE a.authorName IN ('A', 'B')
    ) GROUP BY ab.bookID HAVING COUNT(1) = 2
) bb ON b.bookID = bb.bookID

# ONE MOR WITH GROUP BY AND JOINS
SELECT  b.bookTitle FROM book b
INNER JOIN (
    SELECT ab.bookID FROM author_book ab
	INNER JOIN author a ON (ab.authorID = a.authorID) AND a.authorName = 'A'
) aa ON aa.bookID = b.bookID
INNER JOIN (
    SELECT ab.bookID FROM author_book ab
	INNER JOIN author a ON (ab.authorID = a.authorID) AND a.authorName = 'B'
) aa2 ON aa2.bookID = b.bookID
INNER JOIN author_book ab ON (ab.bookID = b.bookID)
GROUP BY b.bookID, b.bookTitle HAVING COUNT(1) = 2

-- select books written by particular 2 authors, but some other one could be invloved --

# USING GROUP BY
SELECT b.bookTitle FROM book b 
INNER JOIN author_book ab ON ab.bookID = b.bookID
INNER JOIN author a ON a.authorID = ab.authorID
WHERE a.authorName IN ('A', 'B')
GROUP BY ab.bookID HAVING COUNT(1) = 2

# USING SUBSELECT
SELECT b.bookTitle FROM book b
INNER JOIN (
    SELECT ab.bookID FROM author_book ab
    INNER JOIN author a ON a.authorID = ab.authorID
    WHERE a.authorName IN ('A', 'B')
    GROUP BY ab.bookID HAVING COUNT(1) = 2
) bb ON b.bookID = bb.bookID

# USING 4 JOINS 
# CONS: it does not scale if we need condition with N authors
SELECT b.bookTitle FROM book b
INNER JOIN author_book ab ON (ab.bookID = b.bookID)
INNER JOIN author a ON (ab.authorID = a.authorID) AND a.authorName = 'A'
INNER JOIN author_book ab2 ON (ab2.bookID = b.bookID)
INNER JOIN author a2 ON (ab2.authorID = a2.authorID) AND a2.authorName = 'B'

# USING JOINS AND SUBQUERIES
SELECT  b.bookTitle FROM book b
INNER JOIN (
    SELECT ab.bookID FROM author_book ab
	INNER JOIN author a ON (ab.authorID = a.authorID) AND a.authorName = 'A'
) aa ON aa.bookID = b.bookID
INNER JOIN (
    SELECT ab.bookID FROM author_book ab
	INNER JOIN author a ON (ab.authorID = a.authorID) AND a.authorName = 'B'
) aa2 ON aa2.bookID = b.bookID

schema.sql

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;

DROP TABLE IF EXISTS `author`;

CREATE TABLE `author` (
  `authorID` int(11) NOT NULL,
  `authorName` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`authorID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

LOCK TABLES `author` WRITE;
/*!40000 ALTER TABLE `author` DISABLE KEYS */;

INSERT INTO `author` (`authorID`, `authorName`)
VALUES
	(1,'A'),
	(2,'B'),
	(3,'C');

/*!40000 ALTER TABLE `author` ENABLE KEYS */;
UNLOCK TABLES;

DROP TABLE IF EXISTS `author_book`;

CREATE TABLE `author_book` (
  `authorID` int(11) NOT NULL,
  `bookID` int(11) NOT NULL,
  PRIMARY KEY (`authorID`,`bookID`),
  UNIQUE KEY `UNQ_AUTHOR_BOOK` (`authorID`,`bookID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

LOCK TABLES `author_book` WRITE;
/*!40000 ALTER TABLE `author_book` DISABLE KEYS */;

INSERT INTO `author_book` (`authorID`, `bookID`)
VALUES
	(1,1),
	(1,2),
	(1,5),
	(1,7),
	(2,1),
	(2,2),
	(2,3),
	(2,6),
	(2,7),
	(3,2),
	(3,3),
	(3,4),
	(3,5);

/*!40000 ALTER TABLE `author_book` ENABLE KEYS */;
UNLOCK TABLES;

DROP TABLE IF EXISTS `book`;

CREATE TABLE `book` (
  `bookID` int(11) NOT NULL,
  `bookTitle` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`bookID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

LOCK TABLES `book` WRITE;
/*!40000 ALTER TABLE `book` DISABLE KEYS */;

INSERT INTO `book` (`bookID`, `bookTitle`)
VALUES
	(1,'AB'),
	(2,'ABC'),
	(3,'BC'),
	(4,'C'),
	(5,'AC'),
	(6,'B'),
	(7,'AB-dup');

/*!40000 ALTER TABLE `book` ENABLE KEYS */;
UNLOCK TABLES;

/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;