CODEWITHSUNDEEP
mysqlsql
user1844638
user1844638

Reputation: 1073

mysql query not returning expected values

Hi i am writing a mysql query for the following db structure.

Professor (EMP ID,Name,Status,Salary,Age)
Course(Course ID,Course Name,Points)
Works(Course ID,EMP ID,Class ID)
Assumptions:
Each course has only one instructor in each semester
Status can take values from “Full”, “Associate”, and “Assistant”

I need to do the following.

Return the names of full professors who ever taught at least two courses IN one Class

SELECT p.name
FROM professor p, works w
WHERE p.empid = w.empid
AND p.status = ‘full’
AND w.classid IN (SELECT classid
FROM works
WHERE count(courseid)>1)

Return the name(s) of the professor(s) who taught the most number of courses IN Class 10

SELECT p.names
FROM professor p, works w
WHERE p.empid =w.empid
AND w.classid IN (SELECT classid
FROM works
WHERE classid = 10
AND coursed = max(coursed))

But these queries are returning wrong results. I am new to mysql please help.

Upvotes: 0

Views: 103

Answers (2)

Jakub Kania
Jakub Kania

Reputation: 16497

Alternative answer for the first one:

SELECT DISTINCT p.empid, p.name
FROM professor AS p 
JOIN works AS w ON
    p.empid = w.empid
JOIN works w2 ON
    w.empid=w2.empid AND w.classid=w2.classid AND w.courseid<>w2.courseid

Upvotes: 1

Muhammad Raheel
Muhammad Raheel

Reputation: 19882

Try it like this

SELECT 
    p.*,
    COUNT(c.Course_ID) AS TCount
FROM Professor AS P
LEFT JOIN Works AS w ON w.EMP_ID = p.EMP_ID
LEFT JOIN Course AS c ON w.Course_ID = c.Course_ID
GROUP BY p.EMP_ID , c.Course_ID
HAVING TCount > 1

Upvotes: 1

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