我有以下架构
CREATE TABLE years (
year_id INT NOT NULL AUTO_INCREMENT,
year_name_in_nums int NOT NULL,
year_name_in_text varchar(255) NOT NULL,
PRIMARY KEY (year_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE classes (
class_id INT NOT NULL AUTO_INCREMENT,
class_name varchar(255) NOT NULL,
PRIMARY KEY (class_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE students (
student_id INT NOT NULL AUTO_INCREMENT,
student_names varchar(255) NOT NULL,
student_telephone_number int NOT NULL,
PRIMARY KEY (student_id)
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE terms (
term_id INT NOT NULL AUTO_INCREMENT,
term_name_in_nums int NOT NULL,
term_name_in_text varchar(255) NOT NULL,
term_year int NOT NULL,
PRIMARY KEY (term_id),
FOREIGN KEY (term_year) REFERENCES years(year_id) ON DELETE CASCADE ON UPDATE CASCADE
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE class_students (
cs_id INT NOT NULL AUTO_INCREMENT,
cs_class_student int NOT NULL,
cs_class_id int NOT NULL,
cs_term_id int NOT NULL,
PRIMARY KEY (cs_id),
FOREIGN KEY (cs_class_student) REFERENCES students(student_id) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (cs_class_id) REFERENCES classes(class_id) ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (cs_term_id) REFERENCES terms(term_id) ON DELETE CASCADE ON UPDATE CASCADE
)ENGINE=InnoDB DEFAULT CHARSET=utf8;
我想在条款表中显示term_name_in_nums，在年表中显示year_name_in_nums
我以这种方式检索数据
(select term_name_in_nums,term_year from terms INNER JOIN class_students ON term_id=cs_term_id);
从上面可以看出，term_year是一个FOREIGN KEY（term_year），引用年份（year_id）
我正在尝试这个
(select term_name_in_nums from terms INNER JOIN class_students ON term_id=cs_term_id)
LEFT JOIN
(select term_year from terms INNER JOIN class_students ON term_id=cs_term_id);
这给了我一个sql语法错误。我该如何解决这个问题？。
编辑：数据
-- --------------------------------------------------------
-- Host: 127.0.0.1
-- Server version: 5.6.11 - MySQL Community Server (GPL)
-- Server OS: Win32
-- HeidiSQL Version: 8.0.0.4396
-- --------------------------------------------------------
/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!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' */;
-- Dumping data for table algo.classes: ~10 rows (approximately)
/*!40000 ALTER TABLE `classes` DISABLE KEYS */;
INSERT IGNORE INTO `classes` (`class_id`, `class_name`) VALUES
(1, '1'),
(2, '2'),
(3, '3'),
(4, '4'),
(5, '5'),
(6, '6'),
(7, '7'),
(8, '8'),
(9, '9'),
(10, '10');
/*!40000 ALTER TABLE `classes` ENABLE KEYS */;
-- Dumping data for table algo.class_students: ~16 rows (approximately)
/*!40000 ALTER TABLE `class_students` DISABLE KEYS */;
INSERT IGNORE INTO `class_students` (`cs_id`, `cs_class_student`, `cs_class_id`, `cs_term_id`) VALUES
(1, 1, 1, 1),
(2, 1, 1, 1),
(3, 2, 1, 1),
(4, 3, 1, 1),
(5, 4, 1, 1),
(6, 5, 1, 1),
(7, 6, 1, 1),
(8, 7, 1, 1),
(9, 8, 1, 1),
(10, 9, 1, 1),
(11, 10, 1, 1),
(12, 11, 1, 1),
(13, 12, 1, 1),
(14, 13, 1, 1),
(15, 14, 1, 1),
(16, 15, 1, 1);
/*!40000 ALTER TABLE `class_students` ENABLE KEYS */;
-- Dumping data for table algo.examinations: ~3 rows (approximately)
/*!40000 ALTER TABLE `examinations` DISABLE KEYS */;
INSERT IGNORE INTO `examinations` (`examination_id`, `examination_name`, `examination_term_id`) VALUES
(1, 'start of term', 1),
(2, 'mid term', 1),
(3, 'end of term', 1);
/*!40000 ALTER TABLE `examinations` ENABLE KEYS */;
-- Dumping data for table algo.examination_data: ~0 rows (approximately)
/*!40000 ALTER TABLE `examination_data` DISABLE KEYS */;
/*!40000 ALTER TABLE `examination_data` ENABLE KEYS */;
-- Dumping data for table algo.students: ~20 rows (approximately)
/*!40000 ALTER TABLE `students` DISABLE KEYS */;
INSERT IGNORE INTO `students` (`student_id`, `student_names`, `student_telephone_number`) VALUES
(1, 'aa', 123456),
(2, 'bb', 5576899),
(3, '23050359165419520', 788399),
(4, '23050359165419521', 7892020),
(5, '23050359165419522', 33772),
(6, '23050359165419523', 86729),
(7, '23050359165419524', 526890),
(8, '23050359165419525', 444332),
(9, '23050359165419526', 937678),
(10, '23050359165419527', 44),
(11, '23050359165419528', 774),
(12, '23050359165419529', 2147483647),
(13, '23050359165419531', 2147483647),
(14, '23050359165419533', 2147483647),
(15, '23050359165419535', 353657674),
(16, '23050359165419536', 436),
(17, '23050359165419537', 5467),
(18, '23050359165419538', 565788),
(19, '23050359165419539', 548759898),
(20, '23050359165419540', 2443);
/*!40000 ALTER TABLE `students` ENABLE KEYS */;
-- Dumping data for table algo.terms: ~10 rows (approximately)
/*!40000 ALTER TABLE `terms` DISABLE KEYS */;
INSERT IGNORE INTO `terms` (`term_id`, `term_name_in_nums`, `term_name_in_text`, `term_year`) VALUES
(1, 1, 'term one', 1),
(2, 2, 'term two', 2),
(3, 3, 'term three', 3),
(4, 4, 'term four', 4),
(5, 5, 'term five', 5),
(6, 6, 'term six', 6),
(7, 7, 'term seven', 7),
(8, 8, 'term eight', 8),
(9, 9, 'term nine', 9),
(10, 10, 'term ten', 10);
/*!40000 ALTER TABLE `terms` ENABLE KEYS */;
-- Dumping data for table algo.years: ~15 rows (approximately)
/*!40000 ALTER TABLE `years` DISABLE KEYS */;
INSERT IGNORE INTO `years` (`year_id`, `year_name_in_nums`, `year_name_in_text`) VALUES
(1, 2000, '2000/2001'),
(2, 2001, '2001/2002'),
(3, 2002, '2002/2003'),
(4, 2003, '2003/2004'),
(5, 2004, '2004/2005'),
(6, 2005, '2005/2006'),
(7, 2006, '2006/2007'),
(8, 2007, '2007/2008'),
(9, 2008, '2008/2009'),
(10, 2009, '2009/2010'),
(11, 2010, '2010/2011'),
(12, 2011, '2011/2012'),
(13, 2012, '2012/2013'),
(14, 2013, '2013/2014'),
(15, 2014, '2014/2015');
/*!40000 ALTER TABLE `years` ENABLE KEYS */;
/*!40101 SET SQL_MODE=IFNULL(@OLD_SQL_MODE, '') */;
/*!40014 SET FOREIGN_KEY_CHECKS=IF(@OLD_FOREIGN_KEY_CHECKS IS NULL, 1, @OLD_FOREIGN_KEY_CHECKS) */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
答案 0 :(得分：1)
您的查询在两个方面都没有很好的形成。
第一个括号表达没有意义。
在查询结束时，您似乎将此子查询左键连接到顶级查询。但是你还没有为LEFT JOIN提供一个ON子句。你确实为INNER JOIN提供了一个。
select term_year
from terms
INNER JOIN class_students ON term_year=cs_term_id
如果我是你，我会像这样格式化这个查询，在所有表中添加别名（子查询需要别名），并更好地拼写ON子句。我已经添加了最后一个ON条款，但我无法弄清楚你正在尝试用它做什么。
select t.term_name_in_nums, t.term_year
from terms AS t
INNER JOIN class_students AS s ON t.term_id=s.cs_term_id
LEFT JOIN
(
select term_year
from terms
INNER JOIN class_students ON term_year=cs_term_id
) AS y ON y.what = what.what
答案 1 :(得分：1)
你不能像这样使用LEFT JOIN ......你可以使用UNION ALL但这只有在两个查询具有相同数量的列和相同数据类型但是你无法区分这两列时才会起作用因为他们会是一个。尝试像这样对它们进行操作：
SELECT
term_name_in_nums,
NULL as term_year
FROM
terms
INNER JOIN
class_students ON (term_id=cs_term_id)
UNION ALL
SELECT
NULL as term_name_in_nums,
term_year
FROM
terms
INNER JOIN
class_students ON (term_id=cs_term_id)
或尝试执行此查询：
SELECT
terms.term_name_in_nums,
terms_b.term_year
FROM
class_students
INNER JOIN
terms ON (terms.term_id=class_students.cs_term_id)
LEFT JOIN
terms as terms_b ON (terms_b.term_id=class_students.cs_term_id)
我没有要测试的表数据，你想要获得的内容并不是那么清楚。所以无论如何都要尝试一下，你可以编辑它以适应你的情况。
上述数据有助于了解OP之后的内容：
SELECT
class_students.cs_id,
class_students.cs_class_student,
class_students.cs_class_id,
class_students.cs_term_id,
classes.class_name,
students.student_names,
students.student_telephone_number,
terms.term_name_in_nums,
terms.term_name_in_text,
terms.term_year,
years.year_name_in_nums,
year_name_in_text
FROM
class_students
LEFT JOIN classes ON (class_students.cs_class_id=classes.class_id)
LEFT JOIN students ON (class_students.cs_class_student=students.student_id)
LEFT JOIN terms ON (class_students.cs_term_id=terms.term_id)
LEFT JOIN years ON (terms.term_year=years.year_id)
这将为class_students表中的所有记录提供所有课程，学生，学期和年份信息
输出为php数组：
$class_students = array(
array('cs_id' => '1','cs_class_student' => '1','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => 'aa','student_telephone_number' => '123456','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '2','cs_class_student' => '1','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => 'aa','student_telephone_number' => '123456','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '3','cs_class_student' => '2','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => 'bb','student_telephone_number' => '5576899','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '4','cs_class_student' => '3','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419520','student_telephone_number' => '788399','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '5','cs_class_student' => '4','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419521','student_telephone_number' => '7892020','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '6','cs_class_student' => '5','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419522','student_telephone_number' => '33772','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '7','cs_class_student' => '6','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419523','student_telephone_number' => '86729','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '8','cs_class_student' => '7','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419524','student_telephone_number' => '526890','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '9','cs_class_student' => '8','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419525','student_telephone_number' => '444332','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '10','cs_class_student' => '9','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419526','student_telephone_number' => '937678','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '11','cs_class_student' => '10','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419527','student_telephone_number' => '44','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '12','cs_class_student' => '11','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419528','student_telephone_number' => '774','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '13','cs_class_student' => '12','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419529','student_telephone_number' => '2147483647','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '14','cs_class_student' => '13','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419531','student_telephone_number' => '2147483647','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '15','cs_class_student' => '14','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419533','student_telephone_number' => '2147483647','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001'),
array('cs_id' => '16','cs_class_student' => '15','cs_class_id' => '1','cs_term_id' => '1','class_name' => '1','student_names' => '23050359165419535','student_telephone_number' => '353657674','term_name_in_nums' => '1','term_name_in_text' => 'term one','term_year' => '1','year_name_in_nums' => '2000','year_name_in_text' => '2000/2001')
);