I have a table and want to get the average score for each student。
To be more specific, scoremonth1 has more weight to be calculated than 2,3,4,5 and 6 (1>2>3>4>5>6). And we should add no more than 3 monthly scores from the table.
For instance, the average score for Tom should be (80+90)/2 since there are only 2 scores available. As for Marry, the average score should be (90+70+80)/3 since those are the three monthly scores with more weight. And again, for Anna, the average score should be (90+100+70)/3
In my case, there would be over 100 students. Except listing all the possible cases like CASE WHEN scoremonth1 is not null, scoremonth2 is NULL . etc to calculate the average, what else method could do the calculation dynamically?
I know there is a SQL function coalesce to return the first not null value, but how could I get the second and third not null values? And is there a way to track which monthlyscores are added up? I really appreciate your help!
Stu mentioned your underlying issue. To normalize your data without changing table design you can use cross apply...
select student, sum(score)
from table
cross apply (
values(1,scoremonth1),(2,scoremonth2),(3,scoremonth3)) as scores(month,score)
group by student
I strongly suggest you redesign so you don't have to manage this query when adding months by creating a new table called studentScores.
create table studentscores
(
student varchar(200)
,scoremonth int
,score decimal(5,2)
)
And then populate it like this...
insert into studentScores(student,scoremonth,score)
select *
from table
cross apply
(values
(student,1,scoremonth1)
,(student,2,scoremonth2)
,(student,3,scoremonth3)
,(student,4,scoremonth4)
,(student,5,scoremonth5)
) ca(ca1,ca2,ca3)
where ca3 is not null
And finally, usse it like this...
select ss.student, sum(score), count(*) NumOfScores, sum(score)/Count(*) avg
from table
join studentscores ss on ss.student=table.student
where ss.scoremonth between 1 and 3
group by ss.student
Related
All first name should randomly match with each other and when I tried to run query again the First Name should be match with others name. Not the match with FIRST time match.
For example I have 6 records in one table ...
First name column looks like:
JHON
LEE
SAM
HARRY
JIM
KRUK
So I want result like
First name1 First name2
Jhon. Harry
LEE. KRUK
HARRY SAM
The simplest solution is to first randomly sort the records, then calculate the grouping and a sequence number within the group and then finally select out the groups as rows.
You can follow along with the logic in this fiddle: https://dbfiddle.uk/9JlK59w4
DECLARE #Sorted TABLE
(
Id INT PRIMARY KEY,
FirstName varchar(30),
RowNum INT IDENTITY(1,1)
);
INSERT INTO #Sorted (Id, FirstName)
SELECT Id, FirstName
FROM People
ORDER BY NEWID();
WITH Pairs as
(
SELECT *
, (RowNum+1)/2 as PairNum
, RowNum % 2 as Ordinal
FROM #Sorted
)
SELECT
Person1.FirstName as [First name1], Person2.FirstName as [First name2]
FROM Pairs Person1
LEFT JOIN Pairs Person2 ON Person1.PairNum = Person2.PairNum AND Person2.Ordinal = 1
WHERE Person1.Ordinal = 0
ORDER BY Person1.PairNum
ORDER BY NEWID() is used here to randomly sort the records. Note that it is indeterminate and will return a new value with each execution. It's not very efficient, but is suitable for our requirement.
You can't easily use CTE's for producing lists of randomly sorted records because the result of a CTE is not cached. Each time the CTE is referenced in the subsequent logic can result in re-evaluating the expression. Run this fiddle a few times and watch how it often allocates the names incorrectly: https://dbfiddle.uk/rpPdkkAG
Due to the volatility of NEWID() this example stores the results in a table valued variable. For a very large list of records a temporary table might be more efficient.
PairNum uses the simple divide by n logic to assign a group number with a length of n
It is necessary to add 1 to the RowNum because the integer math will round down, see this in action in the fiddle.
Ordinal uses the modulo on the RowNumber and is a value we can use to differentiate between Person 1 and Person 2 in the pair. This helps us keep the rest of the logic determinate.
In the final SELECT we select first from the Pairs that have an Ordinal of 0, then we join on the Pairs that have an Ordinal of 1 matching by the PairNum
You can see in the fiddle I added a solution using groups of 3 to show how this can be easily extended to larger groupings.
I'm trying to find rows with max credit on my table ,
CREATE TABLE Course(
CourseNr INTEGER,
CourseTitel VARCHAR(60),
CourseTyp VARCHAR(10),
CourselenghtDECIMAL,
Credit DECIMAL,
PRIMARY KEY (CourseNr)
);
and there is more than one courses with max value. I dont want to use any default functions for that, any ideas?
Presumably, you want the rows with the maximum credit. A common method is to find any rows that have no larger credit:
select c.*
from course c
where c.credit >= all (select c2.credit from course c2);
Get the rows with Credit for which there don't exist any rows with greater Credit:
SELECT
c.*
FROM Course c
WHERE
NOT EXISTS (
SELECT 1 FROM Course WHERE Credit > c.Credit
)
I have two tables which are joined by an ID...
table 1
- Assessment ID
- Module ID
- Assessment Weighting
table 2
- ID
- AssessmentID
- ModuleID
- UserID
- MarkFrom100
An assessment can have many students taking the assessment.
For example
A module has two assessments, one worth 60% and the other worth 40%. in table 2, I want to take the weighting value from table 1 and multiply it against the mark from 100.
SELECT * FROM Assessment, ModuleAssessmentUser WHERE
INNER JOIN moduleassementuser.assessmentID on Assessment.assessmentID
MULTIPLY AssessmentWeighting BY MarkFrom100 AS finalmark
UserID = 1
I know this is way off, but I really don't know how else to go about it.
My SQL knowledge is limited, so any help is appreciated!
You may use a SUM function in your query which will sum all the data of a certain group in a sub query wich will allow you to multiply the sum to the weight
sub query :
SELECT ModuleID, AssessmentID, UserID, SUM(MarkFrom100) as Total
FROM Table_2
GROUP BY ModuleID
Then use this sub query as a table in a main query :
SELECT T1.Assessment_ID, T1.ModuleID, Q1.UserID (Q1.Total * T1.Assessment_Weighting) as FinalMark
FROM (SELECT ModuleID, UserID, SUM(MarkFrom100) as Total
FROM Table_2
GROUP BY ModuleID) AS Q1
INNER JOIN Table_1 as T1 on T1.ModuleID = Q1.ModuleID
-- WHERE T1.ModuleID = 2 -- a particular module ID
GROUP BY ModuleID;
Note that the WHERE statement is in comment. If you want the whole data, remove it, if you want a particular data, use it ^^
NOTE :
I don't have your database, so it may need some tweeks, but the main idea is there
I m using report tab -> group sort expert-> top n to get top n record but i m getting sum of value in report footer for all records
I want only sum of value of top n records...
In below image i have select top 3 records but it gives sum of all records.
The group sort expert (and the record sort expert too) intervenes in your final result after the total summary is calculated. It is unable to filter and remove rows, in the same way an ORDER BY clause of SQL cannot effect the SELECT's count result (this is a job for WHERE clause). As a result, your summary will always be computed for all rows of your detail section and, of course, for all your group sums.
If you have in mind a specific way to exlude specific rows in order to appear the appropriate sum the you can use the Select Expert of Crystal Reports to remove rows.
Alternatively (and I believe this is the best way), I would make all the necessary calculations in the SQL command and I would sent to the report only the Top 3 group sums (then you can get what you want with a simple total summary of these 3 records)
Something like that
CREATE TABLE #TEMP
(
DEP_NAME varchar(50),
MINVAL int,
RMAVAL int,
NETVAL int
)
INSERT INTO #TEMP
SELECT TOP 3
T.DEP_NAME ,T.MINVAL,T.RMAVAL,T.NETVAL
FROM
(SELECT DEP_NAME AS DEP_NAME,SUM(MINVAL) AS MINVAL,SUM(RMAVAL) AS
RMAVAL,SUM(NETVAL) AS NETVAL
FROM YOURTABLE
GROUP BY DEP_NAME) AS T
ORDER BY MINVAL DESC
SELECT * FROM #TEMP
I currently have a table called tempHouses that looks like:
avgprice | dates | city
dates are stored as yyyy-mm-dd
However I need to move the records from that table into a table called houses that looks like:
city | year2002 | year2003 | year2004 | year2005 | year2006
The information in tempHouses contains average house prices from 1995 - 2014.
I know I can use SUBSTRING to get the year from the dates:
SUBSTRING(dates, 0, 4)
So basically for each city in tempHouses.city I need to get the the average house price from the above years into one record.
Any ideas on how I would go about doing this?
This is an SQL Server approach, and a PIVOT may be a better, but here's one way:
SELECT City,
AVG(year2002) AS year2002,
AVG(year2003) AS year2003,
AVG(year2004) AS year2004
FROM (
SELECT City,
CASE WHEN Dates BETWEEN '2002-01-01T00:00:00' AND '2002-12-31T23:59:59' THEN avgprice
ELSE 0
END AS year2002,
CASE WHEN Dates BETWEEN '2003-01-01T00:00:00' AND '2003-12-31T23:59:59' THEN avgprice
ELSE 0
END AS year2003
CASE WHEN Dates BETWEEN '2004-01-01T00:00:00' AND '2004-12-31T23:59:59' THEN avgprice
ELSE 0
END AS year2004
-- Repeat for each year
)
GROUP BY City
The inner query gets the data into the correct format for each record (City, year2002, year2003, year2004), whilst the outer query gets the average for each City.
There many be many ways to do this, and performance may be the deciding factor on which one to choose.
The best way would be to use a script to perform the query execution for you because you will need to run it multiple times and you extract the data based on year. Make sure that the only required columns are city & row id:
http://dev.mysql.com/doc/refman/5.0/en/insert-select.html
INSERT INTO <table> (city) VALUES SELECT DISTINCT `city` from <old_table>;
Then for each city extract the average values, insert them into a temporary table and then insert into the main table.
SELECT avg(price), substring(dates, 0, 4) dates from <old_table> GROUP BY dates;
Otherwise you're looking at a combination query using joins and potentially unions to extrapolate the data. Because you're flattening the table into a single row per city it's going to be a little tough to do. You should create indexes first on the date column if you don't want the database query to fail with memory limits or just take a very long time to execute.