MySQL Subtraction from a Union - mysql

Question

I have to write a command that uses the following database:
CREATE TABLE `autori` (
`idAutor` mediumint(8) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
`numeAutor` varchar(255) NOT NULL
);
INSERT INTO `autori` (`idAutor`, `numeAutor`) VALUES
(1, 'Ion Creanga'),
(2, 'Walter Scott'),
(3, 'Mihai Eminescu'),
(4, 'George Bacovia'),
(5, 'William Shakespeare'),
(6, 'Agatha Christie'),
(7, 'Jules Verne');
CREATE TABLE `edituri` (
`idEditura` smallint(5) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
`numeEditura` varchar(255) NOT NULL
);
INSERT INTO `edituri` (`idEditura`, `numeEditura`) VALUES
(1, 'Litera'),
(2, 'CARTEA ROMANEASCA'),
(3, 'MONDORO'),
(4, 'RAO'),
(5, 'PENGUIN BOOKS'),
(6, 'Paralela 45'),
(7, 'CASA EDITORIALA DEMIURG PLUS');
CREATE TABLE `carti` (
`idCarte` int(10) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
`titluCarte` varchar(255) NOT NULL,
`idAutor` mediumint(8) UNSIGNED NOT NULL,
`nrPagini` smallint(5) UNSIGNED DEFAULT NULL,
`ISBN` varchar(17) NOT NULL,
`anPublicare` year(4) DEFAULT NULL,
`idEditura` smallint(5) UNSIGNED NOT NULL,
`stoc` smallint(5) UNSIGNED NOT NULL DEFAULT '0',
`refExterna` varchar(255) DEFAULT NULL,
UNIQUE KEY `isbnUnic` (`ISBN`),
FOREIGN KEY (`idAutor`) REFERENCES `autori` (`idAutor`) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (`idEditura`) REFERENCES `edituri` (`idEditura`) ON DELETE CASCADE ON UPDATE CASCADE
);
INSERT INTO `carti` (`idCarte`, `titluCarte`, `idAutor`, `nrPagini`, `ISBN`, `anPublicare`, `idEditura`, `stoc`, `refExterna`) VALUES
(1, 'Amintiri din copilarie', 1, 48, '978-9975-74-380-8', 2014, 1, 5, NULL),
(2, 'Steaua Sudului', 7, 239, '978-973-23-3185-9', 2017, 2, 2, NULL),
(3, 'Sarpele de mare', 7, 199, '978-973-23-3184-2', 2017, 2, 1, NULL),
(4, '20.000 de leghe sub mari', 7, 300, '978-606-695-008-4', 2014, 3, 9, NULL),
(5, 'Crima din Orient Express', 6, 247, '978-606-609-620-1', 2017, 4, 20, NULL),
(6, 'Poirot investigheaza', 6, 217, '978-606-609-277-7', 2012, 4, 1, NULL),
(7, 'Journey to the Centre of the Earth', 7, 254, '978-0-14-062425-0', 1994, 5, 15, NULL),
(8, 'Cele mai frumoase povesti si povestiri', 1, 211, '978-973-47-2074-3', 2015, 6, 64, NULL),
(9, 'Poezii', 3, 382, '978-606-8395-85-2', 2014, 3, 32, NULL),
(10, 'Hamlet', 5, 228, '978-973-152-006-3', 2007, 7, 13, NULL);
CREATE TABLE `tipuriUtilizatori` (
`idTipUtilizator` tinyint(3) UNSIGNED NOT NULL,
`numeTip` varchar(255) NOT NULL
);
INSERT INTO `tipuriUtilizatori` (`idTipUtilizator`, `numeTip`) VALUES
(1, 'Necunoscut'),
(2, 'Bibliotecar'),
(3, 'Student');
CREATE TABLE `utilizatori` (
`idUtilizator` int(10) UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY ,
`numeUtilizator` varchar(255) NOT NULL,
`idTipUtilizator` tinyint(3) UNSIGNED NOT NULL
);
INSERT INTO `utilizatori` (`idUtilizator`, `numeUtilizator`, `idTipUtilizator`) VALUES
(1, 'Xulescu', 3),
(2, 'Ygrec', 3),
(3, 'Zet', 0),
(4, 'Q', 2);
CREATE TABLE `imprumuturi` (
`idUtilizator` int(10) UNSIGNED NOT NULL,
`idCarte` int(10) UNSIGNED NOT NULL,
UNIQUE (`idUtilizator`,`idCarte`),
FOREIGN KEY (`idUtilizator`) REFERENCES `utilizatori` (`idUtilizator`) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (`idCarte`) REFERENCES `carti` (`idCarte`) ON DELETE CASCADE ON UPDATE CASCADE
) ;
INSERT INTO `imprumuturi` (`idUtilizator`, `idCarte`) VALUES
(2, 3),
(3, 4),
(1, 5);
My command needs to return titluCarte, numeAutor, numeEditura, and also to subtract the rows of imprumuturi table from carti.stoc. I have managed to write this, but the subtracting doesn't return 162-3. What am I doing wrong?
SELECT titlucarte,
numeautor,
numeeditura,
stoc
FROM carti
JOIN autori
ON ( carti.idautor = autori.idautor )
JOIN edituri
ON ( carti.ideditura = edituri.ideditura )
UNION
SELECT '--------------------------------------',
'--------',
'--------',
'----'
UNION
SELECT 'total carti',
'--------',
'--------',
Sum(stoc)
FROM carti
UNION
SELECT '--------------------------------------',
'--------',
'--------',
'----'
UNION
SELECT 'carti disponibile',
'--------',
'--------',
Sum(carti.stoc) - (SELECT Count(*)
FROM imprumuturi)
FROM imprumuturi,
carti;
Every other things works well, my problem is with the subtraction from the end of the command.

Answer 1

If you want 159 change your last select query to below.
SELECT 'carti disponibile',
'--------',
'--------',
Sum(carti.stoc) - (SELECT Count(*) FROM imprumuturi)
FROM carti;
DEMO

Answer 2

The reason you get garbage value in the stoc column is because of the 14th line in your above code. Its expecting a number but you are changing the datatype to string and hence the garbage values.
Try changing ----- to a number like 0 for example and you should get the desired output
See below on sql fiddle
http://sqlfiddle.com/#!9/25e5a1/17
SELECT titlucarte,
numeautor,
numeeditura,
stoc
FROM carti
JOIN autori
ON ( carti.idautor = autori.idautor )
JOIN edituri
ON ( carti.ideditura = edituri.ideditura )
UNION
SELECT '--------------------------------------' as 'titlucarte',
'--------' as 'numeautor',
'--------' as 'numeeditura',
/*'----' as 'stoc' */ /*code removed*/
0 as stoc /* code added*/
UNION
SELECT 'total carti' as 'titlucarte',
'--------' as 'numeautor',
'--------' as 'numeeditura' ,
Sum(stoc) as 'stoc'
FROM carti
UNION
SELECT '--------------------------------------' as 'titlucarte',
'--------' as 'numeautor',
'--------' as 'numeeditura' ,
'----' as 'stoc'
UNION
SELECT 'carti disponibile' as 'titlucarte',
'--------' as 'numeautor',
'--------' as 'numeeditura' ,
Sum(carti.stoc) - (SELECT Count(*)
FROM imprumuturi) as 'stoc'
FROM /*imprumuturi,*/
carti;