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I'm trying to display course numbers from table student_enrollment and student names from table students, based on a distinct last_name from table professors. For example, there is a professor named "Wilson" - I would like to only display the courses Wilson's teaching and the students that are enrolled in these classes.
What I have so far is the following, which displays the unique course numbers that each student is enrolled in but does not take into consideration of professors.last_name:
SELECT students.student_name, student_enrollment.course_no
FROM students, student_enrollment, teach
WHERE students.student_no=student_enrollment.student_no
AND student_enrollment.course_no=teach.course_no
GROUP BY student_name,student_enrollment.course_no
Please see the four queried tables (students, student_enrollment, teach, professors) below for more information:
create table students
(
student_no integer,
student_name varchar(20),
age integer
);
insert into students values (1, 'Harpreet', 19);
insert into students values (2, 'Doug', 18);
insert into students values (3, 'Abdul', 21);
insert into students values (4, 'Mohammad', 20);
insert into students values (5, 'Ralph', 19);
insert into students values (6, 'Prateek', 22);
insert into students values (7, 'Michael', 19);
insert into students values (8, 'Jack', 19);
insert into students values (9, 'Chin', 17);
insert into students values (10, '', 20);
create table courses
(
course_no varchar(5),
course_title varchar(20),
credits integer
);
insert into courses values ('CS110', 'Pre Calculus', 4);
insert into courses values ('CS180', 'Physics', 4);
insert into courses values ('CS107', 'Intro to Psychology', 3);
insert into courses values ('CS210', 'Art History', 3);
insert into courses values ('CS220', 'US History', 3);
create table student_enrollment
(
student_no integer,
course_no varchar(5)
);
insert into student_enrollment values (1, 'CS110');
insert into student_enrollment values (1, 'CS180');
insert into student_enrollment values (1, 'CS210');
insert into student_enrollment values (2, 'CS107');
insert into student_enrollment values (2, 'CS220');
insert into student_enrollment values (3, 'CS110');
insert into student_enrollment values (3, 'CS180');
insert into student_enrollment values (4, 'CS220');
insert into student_enrollment values (5, 'CS110');
insert into student_enrollment values (5, 'CS180');
insert into student_enrollment values (5, 'CS210');
insert into student_enrollment values (5, 'CS220');
insert into student_enrollment values (6, 'CS110');
insert into student_enrollment values (7, 'CS110');
insert into student_enrollment values (7, 'CS210');
create table professors
(
last_name varchar(20),
department varchar(12),
salary integer,
hire_date date
);
insert into professors values ('Chong', 'Science', 88000, '2006-04-18');
insert into professors values ('Brown', 'Math', 97000, '2002-08-22');
insert into professors values ('Jones', 'History', 67000, '2009-11-17');
insert into professors values ('Wilson', 'Astronomy', 110000, '2005-01-15');
insert into professors values ('Miller', 'Agriculture', 82000, '2008-05-08');
insert into professors values ('Williams', 'Law', 105000, '2001-06-05');
create table teach
(
last_name varchar(20),
course_no varchar(5)
);
insert into teach values ('Chong', 'CS180');
insert into teach values ('Brown', 'CS110');
insert into teach values ('Brown', 'CS180');
insert into teach values ('Jones', 'CS210');
insert into teach values ('Jones', 'CS220');
insert into teach values ('Wilson', 'CS110');
insert into teach values ('Wilson', 'CS180');
insert into teach values ('Williams', 'CS107');
Note that there may be multiple professors teaching the same course (and there are students enrolled in the same course more than once).
If anyone has a pointer as to what I am missing here, please let me know! I'm new to SQL and have tried a few ideas unsuccessfully.
A simple and quick way to organize the sql is to use sub clause.
select s.*, c.*
from student_enrollment se
inner join student s on se.student_no = s.student_no
inner join course c on se.course_no = c.course_no
where course_no in (select course_no from teach where last_name = 'Wilson')
I am trying to figure out a query for this question: for each major, list the number of students, minimum GPA, maximum GPA, average GPA, minimum age, maximum age, and average age. (Show GPA with 2 decimal points, age with no decimal points. You may find it useful to create a view with one of the previous queries for this one.)
This is the script to create the table for SQL!
REM drop all the tables. Note that you need to drop the
REM dependent table first before dropping the base tables.
drop table Reg;
drop table Student;
drop table Course;
REM Now create all the tables.
create table Student
(
sid char(10) primary key,
sname varchar(20) not null,
gpa float,
major char(10),
dob DATE
);
create table Course
(
cno char(10) primary key,
cname varchar(20) not null,
credits int,
dept char(10)
);
create table Reg
(
sid references Student(sid) on delete cascade,
cno references Course(cno) on delete cascade,
grade char(2),
primary key (sid, cno)
);
REM Now insert all the rows.
insert into Student values ('111', 'Joe', 3.5 , 'MIS', '01-AUG-2000');
insert into Student values ('222', 'Jack', 3.4 , 'MIS', '12-JAN-1999');
insert into Student values ('333', 'Jill', 3.2 , 'CS', '15-MAY-1998');
insert into Student values ('444', 'Mary', 3.7 , 'CS', '17-DEC-2001');
insert into Student values ('555', 'Peter', 3.8 , 'CS', '19-MAR-1999');
insert into Student values ('666', 'Pat', 3.9, 'Math', '31-MAY-2000');
insert into Student values ('777', 'Tracy', 4.0, 'Math', '18-JUL-1997');
insert into Course values ('c101', 'intro', 3 , 'CS');
insert into Course values ('m415', 'database', 4 , 'Bus');
insert into Course values ('m215', 'programming', 4 , 'Bus');
insert into Course values ('a444', 'calculus', 3 , 'Math');
insert into Reg values ('111', 'c101', 'A');
insert into Reg values ('111', 'm215', 'B');
insert into Reg values ('111', 'm415', 'A');
insert into Reg values ('222', 'm215', 'A');
insert into Reg values ('222', 'm415', 'B');
insert into Reg values ('333', 'c101', 'A');
insert into Reg values ('444', 'm215', 'C');
insert into Reg values ('444', 'm415', 'B');
insert into Reg values ('555', 'c101', 'B');
insert into Reg values ('555', 'm215', 'A');
insert into Reg values ('555', 'm415', 'A');
insert into Reg values ('666', 'c101', 'A');
This is what I have so far:
SELECT major,
count(distinct SID) as students,
round(min(gpa), 2),
round(max(gpa), 2),
round(avg(gpa), 2),
trunc(min(sysdate - dob)/365) as min_age,
trunc(max(sysdate - dob)/365) as max_age,
trunc(avg(sysdate - dob)/365) as avg_age,
FROM Student
GROUP BY MAJOR;
According to your input I've made a query that I belive will show you the results. (It was kind hard to read the tables the way you posted it). The syntax may differ according to your DBMS (SQL Server, MySQL, REdshift, Postgres, etc)
Here is the query:
SELECT major,
COUNT(*) as students,
ROUND(MIN(gpa), 2) as min_gpa,
ROUND(MAX(gpa), 2) as max_gpa,
ROUND(AVG(gpa), 2) as avg_gpa,
MIN(DATEDIFF(year, current_date, dob)) as min_age,
MAX(DATEDIFF(year, current_date, dob)) as max_age,
AVG(DATEDIFF(year, current_date, dob)) as avg_date
FROM students st left join Course co on co.dept = st.major
GROUP BY major
Your query is completely fine (just remove comma(,) after avg_age.
SELECT major,
count(distinct SID) as students,
round(min(gpa), 2) as MinGPA,
round(max(gpa), 2) as MaxGPA,
round(avg(gpa), 2) as AvgGPA,
round(min(sysdate - dob)/365,0) as min_age,
round(max(sysdate - dob)/365,0) as max_age,
round(avg(sysdate - dob)/365,0) as avg_age
FROM Student
GROUP BY MAJOR;
You can also use months_between() with floor() to get the same result:
select * from student;
SELECT major,
count(distinct SID) as students,
round(min(gpa), 2) as MinGPA,
round(max(gpa), 2) as MaxGPA,
round(avg(gpa), 2) as AvgGPA,
floor(min(months_between(trunc((sysdate)), dob)) /12) as min_age,
floor(max(months_between(trunc((sysdate)), dob)) /12) as max_age,
floor(avg(months_between(trunc((sysdate)), dob)) /12) as avg_age
FROM Student
GROUP BY MAJOR;
In SQL Server 2008 I have a table People (Id, Gender, Name).
Gender is either Male or Female. There can be many people with the same name.
I would like to write a query that displays for each gender the top 2 names
by count and their count, like this:
Male Female
Adam 23 Rose 34
Max 20 Jenny 15
I think that PIVOT might be used but all the examples I have seen display only one column for each header.
Here is an example on SQL Fiddle -- http://sqlfiddle.com/#!3/b3477/1
This uses an couple of common table expressions to separate the genders.
create table People
(
Id int,
Gender varchar(50),
Name varchar(50)
)
;
insert into People values (1, 'Male', 'Bob');
insert into People values (2, 'Male', 'Bob');
insert into People values (3, 'Male', 'Bill');
insert into People values (4, 'Male', 'Chuck');
insert into People values (5, 'Female', 'Anne');
insert into People values (6, 'Female', 'Anne');
insert into People values (7, 'Female', 'Bobbi');
insert into People values (8, 'Female', 'Jane');
with cteMale as
(
select Name as 'MaleName', Count(*) as Num, ROW_NUMBER() over(order by count(*) desc, Name) RowNum
from People
where Gender = 'Male'
group by Name
)
,
cteFemale as
(
select top 2 Name as 'FemaleName', Count(*) as Num, ROW_NUMBER() over(order by count(*) desc, Name) RowNum
from People
where Gender = 'Female'
group by Name
)
select a.MaleName, a.Num as MaleNum, b.femaleName, b.Num as FemaleNum
from cteMale a
join cteFemale b on
a.RowNum = b.RowNum
where a.RowNum <= 2
Use a windowing function. Below is a complete solution using a temporary table #people.
-- use temp db
use tempdb;
go
-- drop test table
--drop table #people;
--go
-- create test table
create table #people (my_id int, my_gender char(1), my_name varchar(25));
go
-- clear test table
delete from #people;
-- three count
insert into #people values
(23, 'M', 'Adam'),
(34, 'F', 'Rose');
go 3
-- two count
insert into #people values
(20, 'M', 'Max'),
(15, 'F', 'Jenny');
go 2
-- one count
insert into #people values
(20, 'M', 'John'),
(15, 'F', 'Julie');
go
-- grab top two by gender
;
with cte_Get_Top_Two as
(
select ROW_NUMBER() OVER(PARTITION BY my_gender ORDER BY count() DESC) AS my_window,
my_gender, my_name, count() as total
from #people
group by my_gender, my_name
)
select * from cte_Get_Top_Two where my_window in (1, 2)
go
Here is the output.
PS: You can drop my_id from the table since it does not relate to your problem but does not change solution.
Actually, I don't know what is different the following query?
Which one is better(performance, etc...)? Btw, I use SQL Server.
Query 1 :
INSERT INTO PERSON (ID, NAME, ADDRESS) VALUES('001', 'Smit', 'London');
INSERT INTO PERSON (ID, NAME, ADDRESS) VALUES('002', 'Jhon', 'London');
Query 2 : I never saw before
INSERT INTO PERSON (ID, NAME, ADDRESS)
SELECT '001', 'Smit', 'London' UNION ALL
SELECT '002', 'Jhon', 'London'
How about the multi-row syntax with table value constructors:
INSERT INTO PERSON (ID, NAME, ADDRESS)
VALUES ('001', 'Smit', 'London'), ('002', 'Jhon', 'London');
how to convert marks obtained by a student into x%
i.e. there are two exams. calculate certain %marks from both exams (say x% and Y%) so that the total will be 100%
Based on the limited info that you have provided, I think you might be asking for the following:
create table student
(
id int,
s_name varchar(10)
)
insert into student values (1, 'Jim')
insert into student values (2, 'Bob')
insert into student values (3, 'Jane')
create table exams
(
id int,
e_name varchar(10)
)
insert into exams values (1, 'Test 1')
insert into exams values (2, 'Test 2')
insert into exams values (3, 'Test 3')
insert into exams values (4, 'Test 4')
create table exam_student
(
e_id int,
s_id int,
dt datetime,
score decimal(5,2)
)
insert into exam_student values(1, 1, '2012-08-01', 65.0)
insert into exam_student values(1, 2, '2012-08-01', 85.0)
insert into exam_student values(2, 1, '2012-08-02', 75.0)
insert into exam_student values(2, 2, '2012-08-02', 42.0)
select avg(es.score) as ScorePct, s_id, s.s_name
from exam_student es
inner join exams e
on es.e_id = e.id
inner join student s
on es.s_id = s.id
group by s_id, s_name
Results:
If you provide more details on exactly what you are looking for that would be helpful in answering your question.