CREATE TABLE Department(
DNumber integer NOT NULL PRIMARY KEY);
CREATE TABLE Patient(
PID integer NOT NULL PRIMARY KEY,
P_DNumber integer NOT NULL REFERENCES Department (DNumber)
);
CREATE TABLE Appointment(
AppNumber integer NOT NULL PRIMARY KEY,
AppDate date NOT NULL,
App_DNumber integer NOT NULL REFERENCES Department (DNumber)
);
CREATE TABLE Attend(
A_PID integer NOT NULL REFERENCES Patient (PID),
A_AppNumber integer NOT NULL REFERENCES Appointment(AppNumber)
);
HEllo, I have these tables and I want to find for each PID the last Date he attended an appointment. I tried with joins but nothing worked. I am using Postgres. Does anyone have an idea about it?
Thank you very much
Give this a try, joining through Attend and Appointment.
SELECT
Patient.PID,
MAX(Appointment.AppDate) AS lastAttended
FROM
Patient
LEFT JOIN Attend ON Patient.PID = Attend.A_PID
JOIN Appointment ON Appointment.AppNumber = Attend.A_AppNumber
GROUP BY Patient.PID
For patients attending 2+ appointments per month you need COUNT() inside a HAVING clause.
SELECT
Patient.PID,
COUNT(Attend.A_AppNumber) AS numAppts
FROM
Patient
LEFT JOIN Attend ON Patient.PID = Attend.A_PID
GROUP BY Patient.PID
HAVING COUNT(Attend.A_AppNumber) >= 2
Related
There are 3 tables student, course, and takes as following
CREATE TABLE student
(
ID varchar(5),
name varchar(20) NOT NULL,
dept_name varchar(20),
tot_cred numeric(3,0) CHECK (tot_cred >= 0),
PRIMARY KEY (ID),
FOREIGN KEY (dept_name) REFERENCES department
ON DELETE SET NULL
)
CREATE TABLE takes
(
ID varchar(5),
course_id varchar(8),
sec_id varchar(8),
semester varchar(6),
year numeric(4,0),
grade varchar(2),
PRIMARY KEY (ID, course_id, sec_id, semester, year),
FOREIGN KEY (course_id, sec_id, semester, year) REFERENCES section
ON DELETE CASCADE,
FOREIGN KEY (ID) REFERENCES student
ON DELETE CASCADE
)
CREATE TABLE course
(
course_id varchar(8),
title varchar(50),
dept_name varchar(20),
credits numeric(2,0) CHECK (credits > 0),
PRIMARY KEY (course_id),
FOREIGN KEY (dept_name) REFERENCES department
ON DELETE SET NULL
)
tot_cred column data in the student table now is assigned with random values (not correct), I want to perform the query that updates and renews those data based on the course's grade each student has taken. For those students who received F grade will be excluded and those who didn't take any course will be assigned 0 as tot_cred.
I came up with two approaches, one is
UPDATE student
SET tot_cred = (SELECT SUM(credits)
FROM takes, course
WHERE takes.course_id = course.course_id
AND student.ID = takes.ID
AND takes.grade <> 'F'
AND takes.grade IS NOT NULL)
This query meets all my needs, but for those students who didn't take any course, it does assign NULL value instead of 0.
The second is using case when
UPDATE student
SET tot_cred = (select sum(credits)
case
when sum(credits) IS NOT NULL then sum(credits)
else 0 end
FROM takes as t, course as c
WHERE t.course_id = c.course_id
AND t.grade<>'F' and t.grade IS NOT NULL
)
But it assigned 0 to all students. Is any way to achieve the above requirement?
If the 1st query meets your requirement and the only problem is that it returns NULL for the students that did not take any course then the easiest solution would be to use instead of SUM() aggregate function the function TOTAL() which will return 0 instead of NULL:
UPDATE student AS s
SET tot_cred = (
SELECT TOTAL(c.credits)
FROM takes t INNER JOIN course c
ON t.course_id = c.course_id
WHERE t.ID = s.ID AND t.grade <> 'F' AND t.grade IS NOT NULL
);
The same could be done with COALESCE():
SELECT COALESCE(SUM(credits), 0)...
Also, use a proper join with an ON clause and aliases for the tables to improve readability.
CREATE TABLE Course (
courseno VARCHAR(7),
credits INTEGER NOT NULL,
enroll_limit INTEGER,
classroom VARCHAR(10),
PRIMARY KEY(courseNo), );
CREATE TABLE Student (
sID CHAR(8),
sName VARCHAR(30),
major VARCHAR(10),
trackcode VARCHAR(10),
PRIMARY KEY(sID),
FOREIGN KEY (major,trackcode) REFERENCES Tracks(major,trackcode) );
CREATE TABLE Enroll (
courseno VARCHAR(7),
sID CHAR(8),
grade FLOAT NOT NULL,
PRIMARY KEY (courseNo, sID),
FOREIGN KEY (courseNo) REFERENCES Course(courseNo),
FOREIGN KEY (sID) REFERENCES Student(sID) );
So far I've been able to create two seperate queries, one that counts the number of people who failes. And the other counts the number of people who passed. I'm having trouble combining these to produce the number of people passed / number of people failed. For each course.
SELECT course.courseno, COUNT(*) FROM course inner join enroll on enroll.courseno = course.courseno
WHERE course.courseno LIKE 'CptS%' and enroll.grade < 2
GROUP BY course.courseno;
SELECT course.courseno, COUNT(*) FROM course inner join enroll on enroll.courseno = course.courseno
WHERE course.courseno LIKE 'CptS%' and enroll.grade > 2
GROUP BY course.courseno;
The end result should look something like
courseno passrate
CptS451 100
CptS323 100
CptS423 66
You can do a conditional average for this:
select
courseno,
avg(case when grade > 2 then 100.0 else 0 end) passrate
from enroll
where courseno like 'CptS%'
I needed to join three tables Result, ResultITems and GradeScale. When i do, i get double or two of the same row. I tried Creating the records in sqlfiddle but i get a different correct result. The schema i used in creating the tables in my local sqlite db is exactly the same, which is shown here.
The result table
CREATE TABLE Result (
ID INTEGER PRIMARY KEY AUTOINCREMENT,
SubjectID INTEGER REFERENCES Subjects ( ID ) ON DELETE CASCADE,
SessionID INT REFERENCES Sessions ( ID ),
TermID INT REFERENCES terms ( ID ),
ClassID INTEGER REFERENCES Classes ( ID )
);
The resultItems table
CREATE TABLE ResultItems (
StudentID INTEGER,
ResultID INTEGER REFERENCES Result ( ID ) ON DELETE CASCADE,
Total DECIMAL( 10, 2 )
);
And the gradescale table
CREATE TABLE gradeScale
(ID INTEGER PRIMARY KEY AUTOINCREMENT,
minscore tinyint NOT NULL,
maxscore tinyint NOT NULL,
grade char(1) NOT NULL,
ClassCatID INTEGER
);
now when i execute this query below, i et double row for each record in the ResultItems table
Select ri.studentid, ri.Total,g.grade
From ResultItems ri
left join GradeScale g
ON ( ri.total >= g.minscore AND ri.total <= g.maxscore )
left join Result r on r.id=ri.resultid
WHERE r.sessionid = 4
AND
r.termid = 1
AND
r.classid = 9
ORDER BY grade ASC;
Please see the picture below to see what i mean
![enter image description here][1]
and here is the sql fibble which i created http://sqlfiddle.com/#!7/ffb42/1
why am i getting double rows in the output when i execute in my local db?
From #JotaBet's help, i was able to trace the error to the GradeScale table wihci had double entries for each grade letter for each class group.
So i rewrote the sql to take notice of that
left join GradeScale g
ON ( AND c.classcatid = g.classcatid (ri.total >= g.minscore AND ri.total <= g.maxscore) )
Given the schema:
CREATE TABLE Student (
studentID INT PRIMARY KEY NOT NULL,
studentName TEXT NOT NULL,
major TEXT,
class TEXT CHECK (class IN ("Freshman", "Sophomore", "Junior", "Senior")),
gpa FLOAT CHECK (gpa IS NULL OR (gpa >= 0 AND gpa <= 4)),
FOREIGN KEY (major) REFERENCES Dept(deptID) ON UPDATE CASCADE ON DELETE CASCADE
);
CREATE TABLE Dept (
deptID TEXT PRIMARY KEY NOT NULL CHECK (LENGTH(deptID) <= 4),
NAME TEXT NOT NULL UNIQUE,
building TEXT
);
CREATE TABLE Course (
courseNum INT NOT NULL,
deptID TEXT NOT NULL,
courseName TEXT NOT NULL,
location TEXT,
meetDay TEXT NOT NULL CHECK (meetDay IN ("MW", "TR", "F")),
meetTime INT NOT NULL CHECK (meetTime >= '07:00' AND meetTime <= '17:00'),
PRIMARY KEY (courseNum, deptID),
FOREIGN KEY (deptID) REFERENCES Dept(deptID) ON UPDATE CASCADE ON DELETE CASCADE
);
CREATE TABLE Enroll (
courseNum INT NOT NULL,
deptID TEXT NOT NULL,
studentID INT NOT NULL,
PRIMARY KEY (courseNum, deptID, studentID),
FOREIGN KEY (courseNum, deptID) REFERENCES Course ON UPDATE CASCADE ON DELETE CASCADE,
FOREIGN KEY (studentID) REFERENCES Student(studentID) ON UPDATE CASCADE ON DELETE CASCADE
);
I'm attempting to find the names, IDs, and the number of courses they are taking, for the students who are taking the highest number of courses. The sELECT to retrieve the names and IDs is simple enough, however I'm having trouble figuring out how to select the number of courses each student is taking, and then find the max of that and use it as a WHERE clause.
This is what I have so far:
SELECT Student.studentName, Student.studentID, COUNT(*) AS count
FROM Enroll
INNER JOIN Student ON Enroll.studentID=Student.studentID
GROUP BY Enroll.studentID
So first you get count of all the enrolled classes per student
SELECT COUNT() AS num
FROM Enroll
GROUP BY studentID
You can then check that against your existing query using HAVING to get your final query.
SELECT Student.studentName,Student.studentID,COUNT(*) AS count
FROM Enroll
INNER JOIN Student ON Enroll.studentID=Student.studentID
GROUP BY Enroll.studentID
HAVING COUNT()=(SELECT COUNT() AS num FROM Enroll GROUP BY studentID);
So to recap this basically gets the number which represents the highest number of enrollments for any student, then gets all students where that number is their count of enrollments, thus all students which have the highest, or equal highest number of enrollments.
We use HAVING because it is applied after the GROUP BY, meaning you can't use aggregate functions such as COUNT() in a WHERE clause.
I am beginner at SQL and I am trying to create a query.
I have these tables:
CREATE TABLE Hospital (
hid INT PRIMARY KEY,
name VARCHAR(127) UNIQUE,
country VARCHAR(127),
area INT
);
CREATE TABLE Doctor (
ic INT PRIMARY KEY,
name VARCHAR(127),
date_of_birth INT,
);
CREATE TABLE Work (
hid INT,
ic INT,
since INT,
FOREIGN KEY (hid) REFERENCES Hospital (hid),
FOREIGN KEY (ic) REFERENCES Doctor (ic),
PRIMARY KEY (hid,ic)
);
The query is: What is the average in each country of the number of doctors working in hospitals of that country (1st column: each country, 2nd column: average)? Thanks.
You first need to write a query that counts the doctors per hospital
select w.hid, count(w.ic)
from work w
group by w.hid;
Based on that query, you can retrieve the average number of doctors per country:
with doctor_count as (
select w.hid, count(w.ic) as cnt
from work w
group by w.hid
)
select h.country, avg(dc.cnt)
from hospital h
join doctor_count dc on h.hid = dc.hid
group by h.country;
If you have an old DBMS that does not support common table expressions the above can be rewritten as:
select h.country, avg(dc.cnt)
from hospital h
join (
select w.hid, count(w.ic) as cnt
from work
group by w.hid
) dc on h.hid = dc.hid;
Here is an SQLFiddle demo: http://sqlfiddle.com/#!12/9ff79/1
Btw: storing date_of_birth as an integer is a bad choice. You should use a real DATE column.
And work is a reserved word in SQL. You shouldn't use that for a table name.