SQL查詢不能按需運行

Question

我有這個大學數據庫。我必須檢索已經與名爲「John」的教師上課的學生的學生證。

到目前爲止

SELECT student_id 
FROM enrolls 
JOIN teaches ON enrolls.number=teaches.number 
WHERE Instructor.name=(
    SELECT name 
    FROM Instructor 
    WHERE name='john' 
); 

，但是這是行不通的。

create table Course (
    number int, 
    title varchar(255), 
    credits int, 
    syllabus varchar(255), 
    PRIMARY KEY (number) 
); 

INSERT INTO Course VALUES (620,'Algorithm',3,'XYZ'); 
INSERT INTO Course VALUES (232,'Java',2,'ABC'); 
INSERT INTO Course VALUES (420,'Cpp',2,'PQRS'); 
INSERT INTO Course VALUES (720,'Big Data',3,'NVGY'); 
INSERT INTO Course VALUES (120,'Intelligent System',4,'KJHU'); 
INSERT INTO Course VALUES (220,'Operating System',3,'GED'); 
INSERT INTO Course VALUES (480,'Graphics',4,'RSFN'); 
INSERT INTO Course VALUES (520,'Distributed Networks',3,'NHU'); 
INSERT INTO Course VALUES (820,'Data Mining',3,'TYU'); 
INSERT INTO Course VALUES (700,'Cryptography',1,'MNO'); 

create table Student (
    student_id int, 
    name varchar(255), 
    department varchar(255), 
    PRIMARY KEY (student_id) 
); 

INSERT INTO Student VALUES (2345,'Mike','Computer Science'); 
INSERT INTO Student VALUES (346,'Rob','Computer Science'); 
INSERT INTO Student VALUES (789,'Nick','Game Design'); 
INSERT INTO Student VALUES (675,'Sara','Computer Science'); 
INSERT INTO Student VALUES (123,'Raj','Mechanical'); 
INSERT INTO Student VALUES (5331,'Jack','Biotech'); 
INSERT INTO Student VALUES (1023,'Michelle','Chemical'); 
INSERT INTO Student VALUES (9800,'Jie','Industrial'); 
INSERT INTO Student VALUES (7834,'Dan','Petroleum'); 
INSERT INTO Student VALUES (4567,'Patrick','Computer Science'); 


create table Instructor (
    instructor_id int, 
    name varchar(255), 
    department varchar(255), 
    title varchar(255), 
    PRIMARY KEY (instructor_id) 
); 

INSERT INTO Instructor VALUES (12,'John','Computer Science','Java'); 
INSERT INTO Instructor VALUES (23,'Bischof','Mechanical','Drawing'); 
INSERT INTO Instructor VALUES (56,'Kwon','Biotech','Biology'); 
INSERT INTO Instructor VALUES (78,'Deever','Security','Cryptography'); 
INSERT INTO Instructor VALUES (45,'Jin','Computer Science','Cpp'); 
INSERT INTO Instructor VALUES (67,'Bailey','Petroleum','Metalurgy'); 
INSERT INTO Instructor VALUES (90,'Richard','Industrial','Manufacture'); 
INSERT INTO Instructor VALUES (11,'Joe','Chemical','Chemistry'); 
INSERT INTO Instructor VALUES (24,'Roger','Game Design','Cpp'); 
INSERT INTO Instructor VALUES (55,'Zack','Industria','Design'); 


create table CourseOffering (
    number int, 
    year int, 
    semester int, 
    section_number int, 
    classroom int, 
    PRIMARY KEY (number,year,semester,section_number), 
    FOREIGN KEY (number) REFERENCES Course (number) 
); 

INSERT INTO CourseOffering VALUES (620,2012,2,102,3540); 
INSERT INTO CourseOffering VALUES (232,2011,1,103,3455); 
INSERT INTO CourseOffering VALUES (420,2013,3,101,2650); 
INSERT INTO CourseOffering VALUES (720,2013,3,100,3455); 
INSERT INTO CourseOffering VALUES (120,2014,1,102,3000); 
INSERT INTO CourseOffering VALUES (220,2008,2,104,1450); 
INSERT INTO CourseOffering VALUES (480,2009,4,106,1400); 
INSERT INTO CourseOffering VALUES (520,2010,3,102,3500); 
INSERT INTO CourseOffering VALUES (820,2008,3,100,2700); 
INSERT INTO CourseOffering VALUES (700,2012,1,103,2540); 

create table CourseOffering_Timing (
    number int, 
    year int, 
    semester int, 
    section_number int, 
    timing int, 
    PRIMARY KEY (number,year,semester,section_number,timing), 
    FOREIGN KEY (number) REFERENCES Course (number) 
); 

INSERT INTO CourseOffering_Timing VALUES (620,2012,2,102,9); 
INSERT INTO CourseOffering_Timing VALUES (232,2011,1,103,3); 
INSERT INTO CourseOffering_Timing VALUES (420,2013,3,101,2); 
INSERT INTO CourseOffering_Timing VALUES (720,2013,3,100,5); 
INSERT INTO CourseOffering_Timing VALUES (120,2014,1,102,4); 
INSERT INTO CourseOffering_Timing VALUES (220,2008,2,104,10); 
INSERT INTO CourseOffering_Timing VALUES (480,2009,4,106,12); 
INSERT INTO CourseOffering_Timing VALUES (520,2010,3,102,4); 
INSERT INTO CourseOffering_Timing VALUES (820,2008,3,100,2); 
INSERT INTO CourseOffering_Timing VALUES (700,2012,1,103,3); 

create table PreRequisite (
    number int, 
    prerequisite_number int, 
    PRIMARY KEY (number,prerequisite_number), 
    FOREIGN KEY (number) REFERENCES Course(number) 
); 

INSERT INTO PreRequisite VALUES (620,480); 
INSERT INTO PreRequisite VALUES (232,120); 
INSERT INTO PreRequisite VALUES (420,320); 
INSERT INTO PreRequisite VALUES (720,580); 
INSERT INTO PreRequisite VALUES (120,110); 
INSERT INTO PreRequisite VALUES (220,130); 
INSERT INTO PreRequisite VALUES (480,380); 
INSERT INTO PreRequisite VALUES (520,360); 
INSERT INTO PreRequisite VALUES (820,700); 
INSERT INTO PreRequisite VALUES (700,610); 


create table enrolls (
    student_id int, 
    number int, 
    year int, 
    semester int, 
    section_number int, 
    grade varchar(10), 
    PRIMARY KEY (student_id,number,year,semester,section_number), 
    FOREIGN KEY (number,year,semester,section_number) REFERENCES CourseOffering(number,year,semester,section_number), 
    FOREIGN KEY (student_id) REFERENCES Student (student_id) 
); 

INSERT INTO enrolls VALUES (2345,620,2012,2,102,'A'); 
INSERT INTO enrolls VALUES (346,232,2011,1,103,'B'); 
INSERT INTO enrolls VALUES (789,420,2013,3,101,'A'); 
INSERT INTO enrolls VALUES (675,720,2013,3,100,'C'); 
INSERT INTO enrolls VALUES (123,120,2014,1,102,'B'); 
INSERT INTO enrolls VALUES (5331,220,2008,2,104,'A'); 
INSERT INTO enrolls VALUES (1023,480,2009,4,106,'B'); 
INSERT INTO enrolls VALUES (9800,520,2010,3,102,'A'); 
INSERT INTO enrolls VALUES (7834,820,2008,3,100,'C'); 
INSERT INTO enrolls VALUES (4567,700,2012,1,103,'F'); 

create table teaches (
    instructor_id int, 
    number int, 
    year int, 
    semester int, 
    section_number int, 
    PRIMARY KEY (instructor_id, number, year, semester, section_number), 
    FOREIGN KEY (instructor_id) REFERENCES Instructor(instructor_id), 
    FOREIGN KEY (number, year, semester, section_number) REFERENCES CourseOffering(number, year, semester, section_number) 
); 


INSERT INTO teaches VALUES (12,620,2012,2,102); 
INSERT INTO teaches VALUES (23,232,2011,1,103); 
INSERT INTO teaches VALUES (56,420,2013,3,101); 
INSERT INTO teaches VALUES (78,720,2013,3,100); 
INSERT INTO teaches VALUES (45,120,2014,1,102); 
INSERT INTO teaches VALUES (67,220,2008,2,104); 
INSERT INTO teaches VALUES (90,480,2009,4,106); 
INSERT INTO teaches VALUES (11,520,2010,3,102); 
INSERT INTO teaches VALUES (24,820,2008,3,100); 
INSERT INTO teaches VALUES (55,700,2012,1,103); 

Answer 1

你的WHERE子句需要參考您所選擇或連接的表，這是enrolls和teaches之一。所以你將不得不做一些像WHERE teaches.instructor_id=(SELECT instructor_id FROM Instructor WHERE name='john');

PS：你可能也想在你的頂級選擇中拋出一個DISTINCT。

Answer 2

當你的表架構標準化，你需要得到instructor_id，而不是名稱來獲得期望的結果：

SELECT 
    enr.student_id 
FROM 
    enrolls enr JOIN teaches tea ON enr.number = tea.number 
WHERE 
    tea.instructor_id = (
     SELECT instructor_id FROM Instructor WHERE name='john' 
    ); 

Answer 3

我試圖重寫查詢。我可能誤解了，但在這裏它是：

SELECT e.student_id 
FROM enrolls e 
INNER JOIN teaches f ON e.number=f.number 
INNER JOIN Instructor g ON f.instructor_id=g.instructor_id 
WHERE g.name='John' 

http://sqlfiddle.com/#!2/d3181c/3/0

Answer 4

嘗試下面的查詢由於有些時候沒有學生報名參加了這樣的場景教練特定的課程還沒有教他們。

select students.name from teaches 
inner join instructor on teaches.instructor_id= instructor.instructor_id 
inner join enrolls on enrolls.number= teaches.number and enrolls.year= teaches.year 
and enrolls.semester= teaches.semester and enrolls.section_number= teaches.section_number 
inner join students on students.student_id= enrolls.student_id where instructor.name='John';