MySql problem to extract data from two 1to1 tables relationships - mysql

Question

I'm trying to doing this exercise
Extract from the database all the records relating to the "Mathematics" lessons ('docenti.materia' column) of the teacher ('docenti' table) Andrea Bianchi with the participant ('partecipanti' table) Mario Rossi
db sql file
-- phpMyAdmin SQL Dump
-- version 5.2.0
-- https://www.phpmyadmin.net/
--
-- Host: localhost:3306
-- Generation Time: Dec 17, 2022 at 04:13 PM
-- Server version: 8.0.30
-- PHP Version: 8.1.10
SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
START TRANSACTION;
SET time_zone = "+00:00";
/*!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 utf8mb4 */;
--
-- Database: `school`
--
-- --------------------------------------------------------
--
-- Table structure for table `docenti`
--
CREATE TABLE `docenti` (
`id` bigint UNSIGNED NOT NULL,
`id_persona_fisica` bigint UNSIGNED NOT NULL,
`materia` varchar(255) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
--
-- Dumping data for table `docenti`
--
INSERT INTO `docenti` (`id`, `id_persona_fisica`, `materia`) VALUES
(9, 2, 'Matematica'),
(10, 6, 'Storia'),
(11, 3, 'Filosofia');
-- --------------------------------------------------------
--
-- Table structure for table `lezioni`
--
CREATE TABLE `lezioni` (
`id` bigint UNSIGNED NOT NULL,
`id_docente` bigint UNSIGNED NOT NULL,
`giorno` date NOT NULL,
`ora_inizio` time NOT NULL DEFAULT '15:00:00'
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
--
-- Dumping data for table `lezioni`
--
INSERT INTO `lezioni` (`id`, `id_docente`, `giorno`, `ora_inizio`) VALUES
(47, 11, '2022-04-26', '15:00:00'),
(48, 11, '2022-04-19', '15:00:00'),
(49, 11, '2022-12-27', '15:00:00'),
(50, 11, '2022-12-20', '15:00:00'),
(51, 9, '2022-03-30', '15:00:00'),
(52, 9, '2022-04-27', '15:00:00'),
(53, 9, '2022-04-20', '15:00:00'),
(54, 9, '2022-04-13', '15:00:00'),
(55, 9, '2022-12-23', '15:00:00'),
(56, 9, '2022-12-30', '15:00:00'),
(57, 9, '2022-11-25', '15:00:00'),
(58, 9, '2022-11-18', '15:00:00'),
(59, 9, '2022-12-09', '15:00:00'),
(60, 9, '2022-12-04', '15:00:00'),
(61, 10, '2022-12-26', '15:00:00'),
(62, 10, '2022-12-19', '15:00:00'),
(63, 10, '2022-12-12', '15:00:00'),
(64, 10, '2022-11-28', '15:00:00'),
(65, 10, '2022-11-21', '15:00:00'),
(66, 10, '2022-11-14', '15:00:00'),
(67, 10, '2022-04-25', '15:00:00'),
(68, 10, '2022-04-15', '15:00:00'),
(69, 10, '2022-04-11', '15:00:00');
-- --------------------------------------------------------
--
-- Table structure for table `partecipanti`
--
CREATE TABLE `partecipanti` (
`id` bigint UNSIGNED NOT NULL,
`id_persona_fisica` bigint UNSIGNED NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
--
-- Dumping data for table `partecipanti`
--
INSERT INTO `partecipanti` (`id`, `id_persona_fisica`) VALUES
(4, 1),
(2, 4),
(5, 5),
(1, 7),
(3, 8);
-- --------------------------------------------------------
--
-- Table structure for table `persona_fisica`
--
CREATE TABLE `persona_fisica` (
`id` bigint UNSIGNED NOT NULL,
`nome` varchar(255) NOT NULL,
`cognome` varchar(255) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
--
-- Dumping data for table `persona_fisica`
--
INSERT INTO `persona_fisica` (`id`, `nome`, `cognome`) VALUES
(1, 'Mario', 'Rossi'),
(2, 'Andrea', 'Bianchi'),
(3, 'Ernesto', 'Pignoccheri'),
(4, 'Rosa', 'Mastro'),
(5, 'Franco', 'Tilder'),
(6, 'Sara', 'Santelli'),
(7, 'Serena', 'Baropoli'),
(8, 'Franco', 'Baglivi');
-- --------------------------------------------------------
--
-- Table structure for table `presenze`
--
CREATE TABLE `presenze` (
`id` bigint UNSIGNED NOT NULL,
`id_lezione` bigint UNSIGNED NOT NULL,
`id_partecipante` bigint UNSIGNED NOT NULL,
`ora_ingresso` time NOT NULL,
`ora_uscita` time NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
--
-- Dumping data for table `presenze`
--
INSERT INTO `presenze` (`id`, `id_lezione`, `id_partecipante`, `ora_ingresso`, `ora_uscita`) VALUES
(1, 47, 1, '08:00:00', '10:00:00'),
(2, 48, 1, '08:00:00', '10:00:00'),
(3, 49, 1, '08:00:00', '10:00:00'),
(4, 50, 1, '08:00:00', '10:00:00'),
(5, 51, 1, '08:00:00', '10:00:00'),
(6, 52, 1, '08:00:00', '10:00:00'),
(7, 53, 1, '08:00:00', '10:00:00'),
(8, 54, 1, '08:00:00', '10:00:00'),
(9, 55, 1, '08:00:00', '10:00:00'),
(10, 56, 1, '08:00:00', '10:00:00'),
(11, 57, 1, '08:00:00', '10:00:00'),
(12, 58, 1, '08:00:00', '10:00:00'),
(13, 59, 1, '08:00:00', '10:00:00'),
(14, 60, 1, '08:00:00', '10:00:00'),
(15, 61, 1, '08:00:00', '10:00:00'),
(16, 62, 1, '08:00:00', '10:00:00'),
(17, 63, 1, '08:00:00', '10:00:00'),
(18, 64, 1, '08:00:00', '10:00:00'),
(19, 65, 1, '08:00:00', '10:00:00'),
(20, 66, 1, '08:00:00', '10:00:00'),
(21, 67, 1, '08:00:00', '10:00:00'),
(22, 68, 1, '08:00:00', '10:00:00'),
(23, 69, 1, '08:00:00', '10:00:00'),
(24, 68, 2, '08:00:00', '10:00:00'),
(25, 68, 5, '08:00:00', '10:00:00'),
(26, 51, 4, '00:08:00', '00:10:00'),
(27, 52, 4, '00:08:00', '00:10:00'),
(28, 53, 4, '00:08:00', '00:10:00');
--
-- Indexes for dumped tables
--
--
-- Indexes for table `docenti`
--
ALTER TABLE `docenti`
ADD PRIMARY KEY (`id`),
ADD KEY `FK_id_persona_fisica` (`id_persona_fisica`);
--
-- Indexes for table `lezioni`
--
ALTER TABLE `lezioni`
ADD PRIMARY KEY (`id`),
ADD KEY `FK_id_docente` (`id_docente`);
--
-- Indexes for table `partecipanti`
--
ALTER TABLE `partecipanti`
ADD PRIMARY KEY (`id`),
ADD KEY `FK_persona_fisica` (`id_persona_fisica`);
--
-- Indexes for table `persona_fisica`
--
ALTER TABLE `persona_fisica`
ADD PRIMARY KEY (`id`);
--
-- Indexes for table `presenze`
--
ALTER TABLE `presenze`
ADD PRIMARY KEY (`id`),
ADD KEY `FK_id_lezione` (`id_lezione`),
ADD KEY `FK_id_partecipante` (`id_partecipante`);
--
-- AUTO_INCREMENT for dumped tables
--
--
-- AUTO_INCREMENT for table `docenti`
--
ALTER TABLE `docenti`
MODIFY `id` bigint UNSIGNED NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=12;
--
-- AUTO_INCREMENT for table `lezioni`
--
ALTER TABLE `lezioni`
MODIFY `id` bigint UNSIGNED NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=70;
--
-- AUTO_INCREMENT for table `partecipanti`
--
ALTER TABLE `partecipanti`
MODIFY `id` bigint UNSIGNED NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=6;
--
-- AUTO_INCREMENT for table `persona_fisica`
--
ALTER TABLE `persona_fisica`
MODIFY `id` bigint UNSIGNED NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=9;
--
-- AUTO_INCREMENT for table `presenze`
--
ALTER TABLE `presenze`
MODIFY `id` bigint UNSIGNED NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=29;
--
-- Constraints for dumped tables
--
--
-- Constraints for table `docenti`
--
ALTER TABLE `docenti`
ADD CONSTRAINT `FK_id_persona_fisica` FOREIGN KEY (`id_persona_fisica`) REFERENCES `persona_fisica` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;
--
-- Constraints for table `lezioni`
--
ALTER TABLE `lezioni`
ADD CONSTRAINT `FK_id_docente` FOREIGN KEY (`id_docente`) REFERENCES `docenti` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;
--
-- Constraints for table `partecipanti`
--
ALTER TABLE `partecipanti`
ADD CONSTRAINT `FK_persona_fisica` FOREIGN KEY (`id_persona_fisica`) REFERENCES `persona_fisica` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;
--
-- Constraints for table `presenze`
--
ALTER TABLE `presenze`
ADD CONSTRAINT `FK_id_lezione` FOREIGN KEY (`id_lezione`) REFERENCES `lezioni` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
ADD CONSTRAINT `FK_id_partecipante` FOREIGN KEY (`id_partecipante`) REFERENCES `partecipanti` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;
COMMIT;
/*!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 */;
I'm trying with this query but I keep getting a blank line.
SELECT presenze.*, partecipanti.id, partecipanti.id_persona_fisica, persona_fisica.id, persona_fisica.nome, persona_fisica.cognome, docenti.id_persona_fisica, docenti.materia
FROM presenze
JOIN partecipanti ON presenze.id_partecipante = partecipanti.id
JOIN persona_fisica ON partecipanti.id_persona_fisica = persona_fisica.id
JOIN docenti ON docenti.id_persona_fisica = persona_fisica.id
WHERE persona_fisica.nome = 'Mario' AND persona_fisica.cognome = 'Rossi'
AND persona_fisica.nome = 'Andrea' AND persona_fisica.cognome = 'Bianchi'
AND docenti.materia = 'Matematica';
Where am I wrong?
************* S O L V E D *************
In the end I solved it by doing the second JOIN on the 'persona_fisica' table (alias pf2) without putting the 'ON' clause.
Thanks a lot to #blobtub for the tip!
SELECT
presenze.*,
partecipanti.id,
partecipanti.id_persona_fisica,
pf1.id,
pf1.nome,
pf1.cognome,
docenti.id_persona_fisica,
docenti.materia,
pf2.id,
pf2.nome,
pf2.cognome
FROM presenze
JOIN partecipanti
ON presenze.id_partecipante = partecipanti.id
JOIN persona_fisica pf1
ON partecipanti.id_persona_fisica = pf1.id
JOIN persona_fisica pf2
ON docenti.id_persona_fisica = pf2.id
WHERE pf1.nome = 'Mario' AND pf1.cognome = 'Rossi'
AND pf2.nome = 'Andrea' AND pf2.cognome = 'Bianchi'
AND docenti.materia = 'Matematica';

Answer 1

You need to use two joins onto persona_fisica, one for the partecipanti and one for the docenti
See how the persona_fisica table has two relation arrows going from the same attribute (id) on your diagram? This is what tells you you will need two joins if you want to use both relations.
Something like this (I'm afraid my Italian isn't good enough to test it, I'm sorry):
SELECT
lezioni.id_docente,
presenze.*,
partecipanti.id,
partecipanti.id_persona_fisica,
pf1.id,
pf1.nome,
pf1.cognome,
docenti.id_persona_fisica,
docenti.materia,
pf2.id,
pf2.nome,
pf2.cognome
FROM presenze
JOIN partecipanti
ON presenze.id_partecipante = partecipanti.id
JOIN persona_fisica pf1
ON partecipanti.id_persona_fisica = pf1.id
JOIN lezioni
ON presenze.id_lezioni = lezioni.id
JOIN docenti
ON docenti.id = lezioni.id_docenti
JOIN persona_fisica pf2
ON docenti.id_persona_fisica = pf2.id
WHERE pf1.nome = 'Mario' AND pf1.cognome = 'Rossi'
AND pf2.nome = 'Andrea' AND pf2.cognome = 'Bianchi'
AND docenti.materia = 'Matematica';