MySQL Procedure with parameter syntax - mysql

Question

I have a schema with lists of characters from star wars, the movies they appear in, the planets they visit, etc. Here is the schema:
CREATE DATABASE IF NOT EXISTS `starwarsFINAL` /*!40100 DEFAULT CHARACTER SET utf8 */;
USE `starwarsFINAL`;
DROP TABLE IF EXISTS `characters`;
/*!40101 SET #saved_cs_client = ##character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `characters` (
`character_name` varchar(45) NOT NULL,
`race` varchar(45) DEFAULT NULL,
`homeworld` varchar(45) DEFAULT 'Unknown',
`affiliation` varchar(45) DEFAULT NULL,
PRIMARY KEY (`character_name`),
KEY `planet_fk` (`homeworld`),
CONSTRAINT `planet_fk` FOREIGN KEY (`homeworld`) REFERENCES `planets` (`planet_name`) ON DELETE SET NULL ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
/*!40101 SET character_set_client = #saved_cs_client */;
DROP TABLE IF EXISTS `movies`;
/*!40101 SET #saved_cs_client = ##character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `movies` (
`movie_id` int(11) NOT NULL,
`title` varchar(128) DEFAULT NULL,
`scenes_in_db` int(11) DEFAULT NULL,
`scenes_in_movies` int(11) DEFAULT NULL,
PRIMARY KEY (`movie_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
/*!40101 SET character_set_client = #saved_cs_client */;
DROP TABLE IF EXISTS `planets`;
/*!40101 SET #saved_cs_client = ##character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `planets` (
`planet_name` varchar(45) NOT NULL,
`planet_type` varchar(30) DEFAULT NULL,
`affiliation` varchar(30) DEFAULT NULL,
PRIMARY KEY (`planet_name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
/*!40101 SET character_set_client = #saved_cs_client */;
DROP TABLE IF EXISTS `timetable`;
/*!40101 SET #saved_cs_client = ##character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `timetable` (
`character_name` varchar(45) DEFAULT NULL,
`planet_name` varchar(45) DEFAULT 'Unknown',
`movie_id` int(11) DEFAULT NULL,
`arrival` int(11) DEFAULT NULL,
`departure` int(11) DEFAULT NULL,
`time_id` int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`time_id`),
UNIQUE KEY `timetable_un` (`character_name`,`planet_name`,`movie_id`,`arrival`),
KEY `timetable_fkplanet` (`planet_name`),
KEY `timetable_fkmovie` (`movie_id`),
CONSTRAINT `timetable_fkcharacter` FOREIGN KEY (`character_name`) REFERENCES `characters` (`character_name`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `timetable_fkmovie` FOREIGN KEY (`movie_id`) REFERENCES `movies` (`movie_id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `timetable_fkplanet` FOREIGN KEY (`planet_name`) REFERENCES `planets` (`planet_name`) ON DELETE SET NULL ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=57 DEFAULT CHARSET=utf8;
/*!40101 SET character_set_client = #saved_cs_client */;
Here's my problem:
Write a procedure track_planet(planet) that accepts a planet name and returns
a result set that contain the planet name, the movie name, and the number of
characters that appear on that planet during that movie.
Here's what I have so far, but I'm lost/stuck on how to make it work. (I'm new to MySQL)
DROP PROCEDURE IF EXISTS track_planet;
DELIMITER $$
CREATE PROCEDURE track_planet(IN planet VARCHAR(45))
BEGIN
SELECT planet_name FROM planets, title FROM movies,
COUNT(DISTINCT character_name) FROM characters WHERE planet_name = planet;
END
DELIMITER;

Answer 1

Hello_ friend.
First thanks for posting the schema of your database it really helps. From it I was able to made this picture:
And I've changed your code to this:
DELIMITER $$
DROP PROCEDURE IF EXISTS track_planet $$
CREATE PROCEDURE track_planet(IN planet VARCHAR(45))
BEGIN
SELECT
tt.planet_name as planetName, m.title as movieName, COUNT(tt.character_name) as characters
FROM timetable tt
LEFT JOIN movies m ON tt.movie_id = m.movie_id
WHERE tt.planet_name = planet
GROUP BY planetName, movieName;
END $$
DELIMITER ;
The code for the function declaration is pretty much the same except few modifications.
The major change is the SELECT statement:
selecting the necessary columns;
seems that you have most of the information inside timetable so only join movies to get movie name;
use GROUP BY first on planet name and then on movie name so it will count characters on a specific planet by specific movie
and that's it ...
Hope this was helpful. Let me know if it works for you.
Cheers!