sql statement how to keep null value - sql

Question

This query here is executed on 3 tables(students) one which makes a zero on the exam so his q.correctanswer != ur.response, how can I keep the 0 value in my output. When i execute this statement it only gives me two values instead of 3 for each student.
select count(*) as Test1
from users u, question q, userresponse ur
where q.eno = '1'
and q.eno = ur.eno
and q.qno = ur.qno
and ur.response = q.correctanswer
and u.uno = ur.uno
group by u.uno
sample data:
Note:
- "||" is used to concatenate strings
- each string is between a pair of single quotes.
- each record is between "(" and ")".
- fields are ordered according to fields in tables
- "\n" means a new line
======exams data==========
(1,'Java Programming',60,1)
(3,'Elementary History',10,3)
======questions data===========
(1,1,'Choose the operations that can be performed on String
objects:(A) +\n(B) + =\n(C) -\n(D) %\n(E) ^','B')
(1,2,'What will be the result of the expression\na % b\nwhen a and b
are of type int and their values are a = -17 and b = -6?','A')
(1,3,'What will be the result of the expression\na % b\nwhen a and b
are of type int and their values are a = 10 and b = 6?','B')
(1,4,'Consider the following code:\nint x, y, z\ny = 1\nz = 5\nx = 0
- (++y) + z++\nAfter execution of this, what will be the values of x, y and z?','C')
(1,5,'Identify the statements that are correct:\n(A) int a = 13,
a>>2 = 3\n(B) int b = -8, b>>1 = -4\n(C) int a = 13, a>>>2 = 3\n(D)
int b = -8, b>>>1 = -4','E')
(1,6,'If not assigned a value, a variable of type char has the
following default value:','A')
(1,7,'What will be the value of a after execution of the following
statements:\nint a = 23, b = 34\na = ((a < b) ? (b + a) : (b -
a)','B')
(1,8,'Which of the following is not a hexadecimal number?\n(A)
999\n(B) (hex)23\n(C) 0x556\n(D) 0x1F2','C')
(1,9,'if(check4Biz(storeNum) != null) {}\nReferring to the above,
what datatype could be returned by method check4Biz()?','D')
(1,10,'Select the invalid assignment statements from the
following:\n(A) float x = 238.88\n(B) double y = 0x443\n(C) int n =
(int) true\n(D) long m =778645','A')
(1,11,'int j\nfor(int i=0i<14i++) {\nif(i<10) {\nj = 2 +
i\n}\nSystem.out.println("j: " + j + " i: " + i)\n}\nWhat is WRONG
with the above code?','E')
(1,12,'Consider the following code:\nclass ClassA\n{\npublic static
void main(String args [ ])\n{\nClassB b = classB()\n}\nClassA(int x) {
}\n}\nclass ClassB extends ClassA\n{\n}\nWhat will happen when we
compile and run this code?','A')
(1,13,'The keywords reserved but not used in the initial version of
Java are:\n(A) union\n(B) const\n(C) inner\n(D) goto\n(E) boolean\n(F)
synchronized','C')
(1,14,'We would like to make a member of a class visible in all
subclasses regardless of what package they are in. Which one of the
following keywords would achieve this?','D')
(1,15,'Which of the following are not keywords?\n(A) NULL\n(B)
implements\n(C) protected\n(D) extended\n(E) string','B')
(3,1,'The Battle of Gettysburg was fought during which war?','C')
(3,2,'Neil Armstrong and Buzz Aldrin walked how many \n' ||
'minutes on the moon in 1696?','B')
(3,3,'Which Presidents held office during World War II?','D')
(3,4,'In a communist economic system, people:','B')
(3,5,'Which president did not die while in office?','D')
(3,6,'Which state refused to attend the Constitutional Convention
\n' ||
'in 1787 because it didn''t want the United States government \n' ||
'to interfere with already established state affairs?','A')
(3,7,'Who founded Buddhism?','A')
(3,8,'Where is India?','D')
(3,9,'What is the dominant religion in India?','B')
(3,10,'Near which river did archaeologists find India''s \n' ||
'first civilization?','B')
========== answerOption data ============
(3,8,'A','Australia') (3,8,'B','America') (3,8,'C','Africa')
(3,8,'D','Asia') (3,1,'A','World War II') (3,1,'B','The
Revolutionary War') (3,1,'C','The Civil War') (3,1,'D','World War I')
(3,2,'A','123') (3,2,'B','None') (3,2,'C','10') (3,2,'D','51')
(3,3,'A','Franklin D. Roosevelt') (3,3,'B','Dwight D. Eisenhower')
(3,3,'C','Harry Truman') (3,3,'D','Both A and C') (3,4,'A','Are
forced to work as slaves') (3,4,'B','Work for the common good')
(3,4,'C','Work from home computers') (3,4,'D','Don''t work')
(3,5,'A','John F. Kennedy') (3,5,'B','Franklin D. Roosevelt')
(3,5,'C','Abraham Lincoln') (3,5,'D','Ronald Reagan')
(3,5,'E','James A. Garfield') (3,7,'A','Siddharta Gautama')
(3,7,'B','Jesus Christ') (3,7,'C','Mahatma Gandhi')
(3,7,'D','Muhammad') (3,6,'A','Rhode Island') (3,6,'B','New
Hampshire') (3,6,'C','New Jersey') (3,6,'D','New York')
(3,9,'A','Islam') (3,9,'B','Hinduism') (3,9,'C','Christianity')
(3,9,'D','Buddhism') (3,10,'A','The Tiber River') (3,10,'B','The
Indus River') (3,10,'C','The Yellow River') (3,10,'D','The Nile
River') (1,1,'A','(D) & (E)') (1,1,'B',' (A) & (B)') (1,1,'C','(D)')
(1,1,'D','(A)') (1,1,'E','None of these') (1,2,'A','-17')
(1,2,'B','5') (1,2,'C','3') (1,2,'D','-5') (1,2,'E','None of these')
(1,3,'A','1.66') (1,3,'B','4') (1,3,'C','2') (1,3,'D','1')
(1,3,'E','None of these') (1,4,'A','x = 4, y = 1, z = 5') (1,4,'B',' x
= -7, y = 1, z = 5') (1,4,'C','x = 3, y = 2, z = 6') (1,4,'D',' x = 4, y = 2, z = 6') (1,4,'E',' x = 8, y = 2, z = 1') (1,5,'A','(C) & (D) ')
(1,5,'B',' (A), (B) & (C) ') (1,5,'C','(A), (B), (C) & (D)')
(1,5,'D','(A) & (B) ') (1,5,'E','None of the above')
(1,6,'A','\uffff') (1,6,'B','\u0000') (1,6,'C','" " (space)')
(1,6,'D','\u0001') (1,6,'E','None of the above') (1,7,'A','23')
(1,7,'B','Error. Cannot be executed.') (1,7,'C','57') (1,7,'D','11')
(1,7,'E','34') (1,8,'A','(A), (B) & (C)') (1,8,'B','(C)')
(1,8,'C','(A) & (B) ') (1,8,'D','(A)') (1,8,'E','(D)')
(1,9,'A','Boolean') (1,9,'B','Int') (1,9,'C','String')
(1,9,'D','Char') (1,9,'E','Byte') (1,10,'A','(A) & (C)')
(1,10,'B','(A) & (B)') (1,10,'C','(B) ') (1,10,'D','(B) & (D) ')
(1,10,'E','(D)') (1,11,'A','Integer "j" is not initialized.')
(1,11,'B','Nothing.') (1,11,'C','You cannot declare integer i inside
the for-loop declaration.') (1,11,'D','The syntax of the "if"
statement is incorrect.') (1,11,'E','You cannot print integer values
without converting them to strings.') (1,12,'A','Will compile and run
successfully ') (1,12,'B','Error. ClassA does not define a no-argument
constructor ') (1,12,'C','Error. There is no code in the constructor
ClassA(int x) ') (1,12,'D','Error. ClassB does not define a
no-argument constructor ') (1,12,'E','Error. There is no code in the
class ClassB ') (1,13,'A','(C) & (E) ') (1,13,'B','(B),(C) & (D)')
(1,13,'C','(A), (C) & (E)') (1,13,'D','All of these. ')
(1,13,'E','None of these. ') (1,14,'A','private ') (1,14,'B','public')
(1,14,'C','protected') (1,14,'D','private OR protected')
(1,14,'E','All of the above') (1,15,'A','(C), (D) & (E)')
(1,15,'B','(D) ') (1,15,'C','(A), (D) & (E)') (1,15,'D','(D) & (E) ')
(1,15,'E','(A)')
===== users data ====
(1,'1#gmail.com','','George','Ronald','','','Atlanta','GA','30303')
(2,'2#gmail.com','','Mary','Erikson','','','San Diego','CA','91901')
(3,'3#gmail.com','','John','Washington','','','Atlanta','GA','30314')
====enrolls data=====
(1,1,to_date('2012/02/15 10:00:00', 'yyyy/mm/dd
hh24:mi:ss'),to_date('2012/02/22 10:00:00', 'yyyy/mm/dd hh24:mi:ss')
(2,1,to_date('2012/02/15 10:00:00', 'yyyy/mm/dd
hh24:mi:ss'),to_date('2012/02/22 10:00:00', 'yyyy/mm/dd hh24:mi:ss')
(3,1,to_date('2012/02/17 10:00:00', 'yyyy/mm/dd
hh24:mi:ss'),to_date('2012/02/24 10:00:00', 'yyyy/mm/dd hh24:mi:ss')
(1,3,to_date('2012/02/17 10:00:00', 'yyyy/mm/dd
hh24:mi:ss'),to_date('2012/02/24 10:00:00', 'yyyy/mm/dd hh24:mi:ss')
(2,3,to_date('2012/02/20 10:00:00', 'yyyy/mm/dd
hh24:mi:ss'),to_date('2012/02/27 10:00:00', 'yyyy/mm/dd hh24:mi:ss')
(3,3,to_date('2012/02/20 10:00:00', 'yyyy/mm/dd
hh24:mi:ss'),to_date('2012/02/27 10:00:00', 'yyyy/mm/dd hh24:mi:ss')
===userResponse data====
(1,1,1,'A') (1,1,2,'B') (1,1,3,'A') (1,1,4,'B') (1,1,5,'N')
(1,1,6,'C') (1,1,7,'D') (1,1,8,'A') (1,1,9,'B') (1,1,10,'B')
(1,1,11,'A') (1,1,12,'B') (1,1,13,'A') (1,1,14,'A') (1,1,15,'A')
(2,1,1,'B') (2,1,2,'B') (2,1,3,'E') (2,1,4,'C') (2,1,5,'D')
(2,1,6,'A') (2,1,7,'C') (2,1,8,'B') (2,1,9,'B') (2,1,10,'A')
(2,1,11,'A') (2,1,12,'B') (2,1,13,'B') (2,1,14,'A') (2,1,15,'A')
(3,1,1,'C') (3,1,2,'C') (3,1,3,'D') (3,1,4,'D') (3,1,5,'A')
(3,1,6,'A') (3,1,7,'D') (3,1,8,'D') (3,1,9,'A') (3,1,10,'A')
(3,1,11,'B') (3,1,12,'B') (3,1,13,'A') (3,1,14,'A') (3,1,15,'C')
(1,3,1,'N') (1,3,2,'A') (1,3,3,'A') (1,3,4,'B') (1,3,5,'B')
(1,3,6,'C') (1,3,7,'D') (1,3,8,'A') (1,3,9,'A') (1,3,10,'B')
(2,3,1,'B') (2,3,2,'C') (2,3,3,'A') (2,3,4,'C') (2,3,5,'B')
(2,3,6,'D') (2,3,7,'D') (2,3,8,'D') (2,3,9,'A') (2,3,10,'A')
(3,3,1,'B') (3,3,2,'A') (3,3,3,'A') (3,3,4,'B') (3,3,5,'B')
(3,3,6,'C') (3,3,7,'D') (3,3,8,'A') (3,3,9,'A') (3,3,10,'B')
Thanks,

Answer 1

What I think you're asking is "how many questions did any user get right?" If so, based on the query you have - and the fact that there's no direct relation between users and questions - I've come up with the following:
select u.uno, sum(case ur.response when null then 0 else 1 end) as Test1
from question q
cross join users u
left join userresponse ur
on q.eno = ur.eno
and q.qno = ur.qno
and q.correctanswer = ur.response
and u.uno = ur.uno
where q.eno = '1'
group by u.uno
So we do a cartesion join between users and questions, because we don't have a better way to join them. We then do an left outer join against the userresponse table; unless everything matches correctly, the user either didn't answer the question or answered it wrong. We cast whether or not that value's null to a 0 if null and 1 if if it's not, so the sum of those is the number of correct answers per user.

Answer 2

If I've understood your query correctly, the following ought to work. It uses the old Oracle join syntax:
SELECT u.uno, COUNT(*)
FROM users u, userresponse ur, question q
WHERE u.uno = ur.uno
AND ur.response = q.correctanswer(+)
AND ur.eno = q.eno(+)
AND ur.qno = q.qno(+)
AND q.eno(+) = 1
GROUP BY u.uno

Answer 3

I think that you are trying to get all users and the associated quiz score. If I understood correctly, then using appropriate joins clauses, you can easily get the expected results:
select u.uno, count (ur.response) as NumberAnswered, count (q.correctanswer) as NumberCorrect
from users u
join userresponse ur --inner join means we limit user rows to users who have responses
on u.uno = ur.uno
left outer join question q --outer join means we look for row data, but don't exclude users based on the fact that the row doesn't match the join conditions
on ur.response = q.correctanswer
and q.eno = 1 --only include rows where the question.eno value is 1(?)
and q.eno = ur.eno --only include rows where question.eno and userresponse.eno are the same (the answer was correct)
group by u.uno