Hit a roadblock and hoping someone here is able to help please?
edit: DB<>FIDDLE : https://dbfiddle.uk/?rdbms=mysql_5.5&fiddle=c73f8ec9a60f530fe4ad489dc743f9b9
I have 3 tables:
marks - which uses grades;
target - which also uses grades;
grades - a lookup for grades to points.
What I am trying to do is calculate the total points for grades within the marks table, then calculate the total target points by multiplying the points value for the target by the number of grades within the marks table for a given person (adno).
I'm able to sum and count the points values from the marks table without a problem, but as I've used an inner joint for the marks to grades already I cannot add a further one for target to grades so I've used a subquery.
However when I try to use the result of subquery (EDIT single_target_points , not target_points as I originally posted) in the calculation in the line straight after it I get the error :
[Err] 1054 - Unknown column 'single_target_points' in 'field list'
This is the query I am trying:
SELECT
marks.adno,
Sum(grades.points) AS total_points,
Count(grades.points) AS no_of_subjects,
(SELECT grades.points FROM targets INNER JOIN grades ON targets.grade = grades.grade WHERE targets.adno = marks.adno GROUP BY grades.points) AS single_target_points,
single_target_points*no_of_subjects AS target_points
FROM
marks
INNER JOIN grades ON marks.resultvalue = grades.grade
INNER JOIN targets ON targets.adno = marks.adno
GROUP BY
marks.adno
This will resolve the query for you, but not sure what you are doing is completely accurate. I took your in-line query and made it a subquery including the "adno" (person id) to get all distinct points. Using that and JOINING based on the person like the others.
SELECT
m.adno,
Sum(g.points) AS total_points,
Count(g.points) AS no_of_subjects,
SUM( TP.single_target_points * g.points) AS target_points
FROM
marks m
JOIN grades g
ON m.resultvalue = g.grade
JOIN students s
ON m.adno = s.adno
JOIN targets t
ON m.adno = t.adno
JOIN
( SELECT distinct
t2.adno,
t2.grade,
g2.points single_target_points
FROM
targets t2
JOIN grades g2
ON t2.grade = g2.grade ) TP
on t.adno = TP.adno
and t.grade = TP.grade
GROUP BY
m.adno
Now, that being said, it looks like you are trying to compute a person's GPA (grade point average). If you can EDIT your existing post and provide samples of data (use spaces to align, not tabs) even if fictional names (but not necessary since things here are all ID values and otherwise not private). It would help to see the basis of what computations are going on. If not done correctly, you will get Cartesian results and skew your points due to multiple entries * multiple entries = oversized expected answer values.
Also, I Updated your dbfiddle. You inserted into adno instead of students the sample records, inserted into targets the grades, so those tables were blank. I had to correct that. Then changed grades to integer since doing math (via sum( g.points)). Best to use proper data types vs everything as character.
At least the queries are now working, but does not make sense if this is GPA calculations -- as far as I know and have done for U.S. college transcript purposes.
Related
I was given the following question for an assignment
Write a SQL statement to show the sum of Hours Worked for each Type of OWNER but exclude services of employees who have Experience Level of Junior and exclude any Owner Type with Less Than Four members
I'm having a hard time figuring out how to accomplish the last part of the question. I believe that it would require counting a portion of a select statement but I'm not sure how to do that.
So far, this is what I have:
SELECT SUM(HoursWorked), OwnerType
FROM PROPERTY_SERVICE
JOIN EMPLOYEE ON EMPLOYEE.EmployeeID=PROPERTY_SERVICE.EmployeeID
JOIN OWNED_PROPERTY ON OWNED_PROPERTY.PropertyID = PROPERTY_SERVICE.PropertyID
INNER JOIN OWNER ON OWNER.OwnerID=OWNED_PROPERTY.OwnerID
WHERE NOT EMPLOYEE.ExperienceLevel='Junior'
*This is where I believe the solution should go*
GROUP BY OWNER.OwnerType;
Presumably, you just want a HAVING clause:
SELECT SUM(HoursWorked), o.OwnerType
FROM PROPERTY_SERVICE ps
JOIN EMPLOYEE e ON e.EmployeeID = ps.EmployeeID
JOIN OWNED_PROPERTY op ON op.PropertyID = ps.PropertyID
INNER JOIN OWNER o ON o.OwnerID = op.OwnerID
WHERE e.ExperienceLevel <> 'Junior'
GROUP BY o.OwnerType
HAVING COUNT(*) < 4
This excludes groups of rows having the same OwnerType that contain less than 4 rows. You might need to adjust the expression to your exact definition of a member.
Note that I added table aliases to the query to make it easier to read and write. I would also recommend prefixing column HoursWorked with the table it belongs to, to avoid ambiguity.
I've never been able to get my head around INNER JOINs (or any other JOIN types for that matter) so I'm struggling to work out how to use it in my specific situation. In fact, I'm not even sure if it's what I need. I've looked at other examples and read tutorials but my brain just doesn't seem to work the way needed to truly get it (or it doesn't function at all).
Here's the scenario:
I have two tables -
phone_numbers - this table has a list of phone numbers that
belong to lots of different customers. A single customer can have
multiple numbers. For simplicity's sake, we'll say the fields are
'number_id', 'customer_id', 'phone_number'.
call_history - this table has a record of every single call that one of these
numbers in the first table could have had. There's a record for
every individual call going back years. Again, for simplicity,
we'll say the relevant fields are customer_id, phone_number,
call_start_time.
What I'm trying to accomplish is to find all of the numbers that belong to a particular customer_id in the phone numbers table and use that information to search through the call_history table and find the number of calls each phone number has received, and group that by the number of calls for each number, preferably also showing zeros where a number hasn't received any calls at all.
The reason the zero calls is important is because that's the data I'm interested in. Otherwise, I could just get all the information out of the call_history table. But what I'm trying to achieve is find the numbers with no activity.
All I've been able to accomplish is run one query to get all of the numbers belonging to one customer:
SELECT customer_id, phone_number FROM phone_numbers WHERE customer_id = Y;
Then run a second query to get all phone calls for that customer_id for a set duration:
SELECT customer_id, phone_number, COUNT(*) FROM call_history WHERE customer_id = Y and call_start_time >= DATE_SUB(SYSDATE(), INTERVAL 30 DAY) GROUP BY phone_number;
I've then had to use the data returned from both queries and use a VLOOKUP function in Excel to match number of calls for each individual number from the second query to the list of all numbers from the first query, thus leaving blanks in my "all numbers" table and identifying those numbers that had no calls for that time period.
I'm hoping there's some way to do all of this with a single query and return a table of results, listing the zero number of calls with it and eliminate the whole manual Excel bit as it's not overly efficient and prone to human error.
Without at least a workable example from you, it's not easy to re-create your situation. Anyway, INNER JOIN might not return the result as how you expected. In my short time with MySQL, I mainly use 2 types of JOIN; one is already mentioned and the other is LEFT JOIN. From what I can understand in your question, what you want to achieve can be done by using LEFT JOIN instead of INNER JOIN. I may not be the best person to explain this to you but this is how I understand it:
INNER JOIN - only return anything that match in ON clause between two (or more) tables.
LEFT JOIN - will return everything from the table on the left side of the join and return NULL if ON get no match in the table on the right side of the join .. unless you specify some WHERE condition from something on the right table.
Now, here is my query suggestion and hopefully it'll be useful for you:
SELECT A.customer_id, A.phone_number,
SUM(CASE WHEN call_start_time >= DATE_SUB(SYSDATE(), INTERVAL 30 DAY)
THEN 1 ELSE 0 END) AS Total
FROM phone_numbers A
LEFT JOIN call_history B
ON A.customer_id=B.customer_id
GROUP BY A.customer_id,A.phone_number;
What I did here is I LEFT JOIN phone_numbers table with call_history on customer_id and I re-position the WHERE call_start_time >= .. condition into a CASE expression in the SELECT since putting it at WHERE will turn this into a normal join or inner join instead.
Here is an example fiddle : https://www.db-fiddle.com/f/hriFWqVy5RGbnsdj8i3aVG/1
For Inner join You should have to do like this way..
SELECT customer_id,phone_number FROM phone_numbers as pn,call_history as ch where pn.customer_id = ch.customer_id and call_start_time >= DATE_SUB(SYSDATE(), INTERVAL 30 DAY) GROUP BY phone_number;
Just add table name whatever you want to join and add condition
I'm trying to write a query which does the below:
For every guest who has the word “Edinburgh” in their address show the total number of nights booked. Be sure to include 0 for those guests who have never had a booking. Show last name, first name, address and number of nights. Order by last name then first name.
I am having problems with making the join work properly,
ER Diagram Snippet:
Here is my current (broken) solution:
SELECT last_name, first_name, address, nights
FROM booking
RIGHT JOIN guest ON (booking.booking_id = guest.id)
WHERE address LIKE '%Edinburgh%';
Here is the results from that query:
The query is partially complete, hoping someone can help me out and create a working version. I'm currently in the process of learning SQL so apologies if its a rather basic or dumb question!
Your query seems almost correct. You were joining the booking id with guets id which gave you some results because of overlapping (matching) ids, but this most likely doesn't correspond to the foreign keys. You should join on guest_id from booking to id from guest.
I'd add grouping to sum all booked nights for a particular guest (assuming that nights is an integer):
SELECT g.last_name, g.first_name, g.address, SUM(b.nights) AS nights
FROM guest AS g
LEFT JOIN booking AS b ON b.guest_id = g.id
WHERE g.address LIKE '%Edinburgh%'
GROUP BY g.last_name, g.first_name, g.address;
Are you sure that nights spent should be calculated using nights field? Why can it be null? If you'd like to show zero for null values just wrap it up with a coalesce function like that:
COALESCE(SUM(b.nights), 0)
Notes:
Rewriten RIGHT JOIN into LEFT JOIN, but that doesn't affect results - it's just cleaner for me
Using aliases eg. AS g makes the code shorter when specifying joining columns
Reference every column with their table alias to avoid ambiguity
SELECT g.first_name,
g.last_name,
g.address,
COALESCE(Sum(b.nights), 0)
FROM booking b
RIGHT JOIN guest g
ON ( b.guest_id = g.id )
WHERE address LIKE 'edinburgh%'
GROUP BY g.last_name,
g.first_name,
g.address;
This post answers your questions about how to make the query.
MySQL SUM with same ID
You can simply use COALESCE as referenced here to avoid the NULL Values
How do I get SUM function in MySQL to return '0' if no values are found?
I am using the following JOIN statement:
SELECT *
FROM students2014
JOIN notes2014 ON (students2014.Student = notes2014.NoteStudent)
WHERE students2014.Consultant='$Consultant'
ORDER BY students2014.LastName
to retrieve a list of students (students2014) and corresponding notes for each student stored in (notes2014).
Each student has multiple notes within the notes2014 table and each note has an ID that corresponds with each student's unique ID. The above statement is returning a the list of students but duplicating every student that has more than one note. I only want to display the latest note for each student (which is determined by the highest note ID).
Is this possible?
You need another join based on the MAX noteId you got from your select.
Something like this should do it (not tested; next time I'd recommed you to paste a link to http://sqlfiddle.com/ with your table structure and some sample data.
SELECT *
FROM students s
LEFT JOIN (
SELECT MAX(NoteId) max_id, NoteStudent
FROM notes
GROUP BY NoteStudent
) aux ON aux.NoteStudent = s.Student
LEFT JOIN notes n2 ON aux.max_id = n2.NoteId
If I may say so, the fact that a table is called students2014 is a big code smell. You'd be much better off with a students table and a year field, for many reasons (just a couple: you won't need to change your DB structure every year, querying across years is much, much easier, etc, etc). Perhaps you "inherited" this, but I thought I'd mention it.
GROUP the query by studentId and select the MAX of the noteId
Try :
SELECT
students2014.Student,
IFNULL(MAX(NoteId),0)
FROM students2014
LEFT JOIN notes2014 ON (students2014.Student = notes2014.NoteStudent)
WHERE students2014.Consultant='$Consultant'
GROUP BY students2014.Student
ORDER BY students2014.LastName
I have 2 simple tables - Firm and Groups. I also have a table FirmGroupsLink for making connections between them (connection is one to many).
Table Firm has attributes - FirmID, FirmName, City
Table Groups has attributes - GroupID, GroupName
Table FirmGroupsLink has attributes - FrmID, GrpID
Now I want to make a query, which will return all those firms, that have less groups then #num, so I write
SELECT FirmID, FirmName, City
FROM (Firm INNER JOIN FirmGroupsLink ON Firm.FirmID =
FirmGroupsLink.FrmID)
HAVING COUNT(FrmID)<#num
But it doesn't run, I try this in Microsoft Access, but it eventually should work for Sybase. Please show me, what I'm doing wrong.
Thank you in advance.
In order to count properly, you need to provide by which group you are couting.
The having clause, and moreover the count can't work if you are not grouping.
Here you are counting by Firm. In fact, because you need to retrieve information about the Firm, you are grouping by FirmId, FirmName and City, so the query should look like this:
SELECT Firm.FirmID, Firm.FirmName, Firm.City
FROM Firm
LEFT OUTER JOIN FirmGroupsLink
ON Firm.FirmID = FirmGroupsLink.FrmID
GROUP BY Firm.FirmID, Firm.FirmName, Firm.City
HAVING COUNT(FrmID) < #num
Note that I replace the INNER JOIN by a LEFT OUTER JOIN, because you might want Firm which doesn't belongs to any groups too.