I've 3 tables as under
MERCHANDISE
+-----------+-----------+---------------+
| MERCH_NUM | MERCH_DIV | MERCH_SUB_DIV |
+-----------+-----------+---------------+
| 1 | car | awd |
| 1 | car | awd |
| 2 | bike | 1kcc |
| 3 | cycle | hybrid |
| 3 | cycle | city |
| 4 | moped | fixie |
+-----------+-----------+---------------+
PRIORITY
+----------+-----------+---------+---------+------------+------------+---------------+
| CUST_NUM | SALES_NUM | DOC_NUM | BALANCE | PRIORITY_1 | PRIORITY_2 | PRIORITY_CODE |
+----------+-----------+---------+---------+------------+------------+---------------+
| 90 | 1000 | 10 | 23 | 1 | 6 | NO |
| 91 | 1001 | 20 | 32 | 3 | 7 | PRI |
| 92 | 1002 | 30 | 11 | 2 | 8 | LATE |
| 93 | 1003 | 40 | 22 | 5 | 9 | 1MON |
+----------+-----------+---------+---------+------------+------------+---------------+
ORDER
+----------+-----------+---------+---------+-----------+-----------+
| CUST_NUM | SALES_NUM | DOC_NUM | COUNTRY | MERCH_NUM | MERCH_DIV |
+----------+-----------+---------+---------+-----------+-----------+
| 90 | 1000 | 10 | INDIA | 1 | car |
| 91 | 1001 | 20 | CHINA | 2 | bike |
| 92 | 1002 | 30 | USA | 3 | cycle |
| 93 | 1003 | 40 | UK | 4 | moped |
+----------+-----------+---------+---------+-----------+-----------+
I want to join the left joined table from the last two tables with the first one such that the MERCH_SUB_DIV 'awd' appears only once for each unique combination of merch_num and merch_div
the code I came up with is as under, but I'm not sure how do I eliminate the duplicate row just for the awd
select
ROW#, MERCH.MERCH_NUMBER, ORDPRI.MERCH_NUMBER, ORDPRI.CUST_NUM,
BALANCE, SALES_NUM, ITEM_NUM, RANK, PRIORITY_1
from (
select
ROW_NUMBER() OVER(
PARTITION BY ORD.DOC_NUM, ORD.ITEM_NUM
ORDER BY ORD.DOC_NUM, ORD.ITEM_NUM ASC
) AS Row#,
ORD.CUST_NUM, PRI.CUST_NUM, ORD.MERCH_NUM, ORD.MERCH_DIV, PRI.BALANCE,
pri.DOC_NUM, pri.SALES_NUM, pri.PRIORITY_1, pri.PRIORITY_2
from ORDER as ORD
left join PRIORITY as PRI on ORD.DOC_NUM = PRI.DOC_NUM
and ORD.SALES_NUMBER = PRI.SALES_NUM
where country_name in ('USA', ‘INDIA’)
) as ORDPRI
left join MERCHANDISE as MERCH on ORDPRI.DIV = MERCH.DIV
and ORDPRI.MERCH_NUM = MERCH.MERCH_NUM
You have to use 'DISTINCT' keyword to get unique values, but if your 'Priority table' & 'Order table' contains different values for Same MERCH_NUM then the final result contains the repetation of the 'MERCH_NUM'.
SELECT DISTINCT M.MERCH_NUMBER, O.MERCH_NUMBER, O.CUST_NUM, BALANCE, SALES_NUM,ITEM_NUM,RANK,PRIORITY_1
FROM priority_table P
LEFT JOIN order_table O ON P.CUST_NUM = O.CUST_NUM AND P.SALES_NUM=O.SALES_NUM AND P.DOC_NUM = O.DOC_NUM
LEFT JOIN merchandise_table M ON M.MERCH_NUM = O.MERCH_NUM
A way around can be to add one new Row_Number() in the outermost query having Partition by MERCH_SUB_DIV + all the columns in the final list and then filter final results based on the New Row_Number() . Follows a pseudo code that might help:
select
-- All expected columns in final result except the newRow#
ROW#, MERCH_NUM, CUST_NUM,
BALANCE, SALES_NUM, PRIORITY_1
from (
select
ROW#,
-- the new row number includes all column you want to show in final result
row_number() over ( PARTITION BY MERCH.MERCH_SUB_DIV ,
MERCH.MERCH_NUM, ORDPRI.MERCH_NUM, ORDPRI.CUST_NUM,
BALANCE, SALES_NUM, PRIORITY_1
order by (select 1 )) as newRow# ,
MERCH.MERCH_NUM, ORDPRI.CUST_NUM,
BALANCE, SALES_NUM, PRIORITY_1
from (
-- main query goes here
select
ROW_NUMBER() OVER(
PARTITION BY ORD.DOC_NUM --, ORD.ITEM_NUM
ORDER BY ORD.DOC_NUM ASC --, ORD.ITEM_NUM
) AS Row#,
ORD.CUST_NUM, ORD.MERCH_NUM, ORD.MERCH_DIV as DIV, PRI.BALANCE,
pri.DOC_NUM, pri.SALES_NUM, pri.PRIORITY_1, pri.PRIORITY_2
from #ORDER as ORD
left join #PRIORITY as PRI on ORD.DOC_NUM = PRI.DOC_NUM
and ORD.SALES_NUMBER = PRI.SALES_NUM
where country_name in ('USA', 'INDIA')
) as ORDPRI
left join #MERCHANDISE as MERCH on ORDPRI.DIV = MERCH.DIV
and ORDPRI.MERCH_NUM = MERCH.MERCH_NUM
) as T
-- final filter to get distinct values
where newRow# = 1
Sample code here .. Hope this helps!!
The concerned tables are as follows:
students(rollno, name, deptcode)
depts(deptcode, deptname)
course(crs_rollno, crs_name, marks)
The query is
Find the name and roll number of the students from each department who obtained
highest total marks in their own department.
Consider:
i) Courses of different department are different.
ii) All students of a particular department take same number and same courses.
Then only the query makes sense.
I wrote a successful query for displaying the maximum total marks by a student in each department.
select do.deptname, max(x.marks) from students so
inner join depts do
on do.deptcode=so.deptcode
inner join(
select s.name as name, d.deptname as deptname, sum(c.marks) as marks from students s
inner join crs_regd c
on s.rollno=c.crs_rollno
inner join depts d
on d.deptcode=s.deptcode
group by s.name,d.deptname) x
on x.name=so.name and x.deptname=do.deptname group by do.deptname;
But as mentioned I need to display the name as well. Accordingly if I include so.name in select list, I need to include it in group by clause and the output is as below:
Kendra Summers Computer Science 274
Stewart Robbins English 80
Cole Page Computer Science 250
Brian Steele English 83
expected output:
Kendra Summers Computer Science 274
Brian Steele English 83
Where is the problem?
I guess this can be easily achieved if you use window function -
select name, deptname, marks
from (select s.name as name, d.deptname as deptname, sum(c.marks) as marks,
row_number() over(partition by d.deptname order by sum(c.marks) desc) rn
from students s
inner join crs_regd c on s.rollno=c.crs_rollno
inner join depts d on d.deptcode=s.deptcode
group by s.name,d.deptname) x
where rn = 1;
To solve the problem with a readable query I had to define a couple of views:
total_marks: For each student the sum of their marks
create view total_marks as select s.deptcode, s.name, s.rollno, sum(c.marks) as total from course c, students s where s.rollno = c.crs_rollno group by s.rollno;
dept_max: For each department the highest total score by a single student of that department
create view dept_max as select deptcode, max(total) max_total from total_marks group by deptcode;
So I can get the desidered output with the query
select a.deptcode, a.rollno, a.name from total_marks a join dept_max b on a.deptcode = b.deptcode and a.total = b.max_total
If you don't want to use views you can replace their selects on the final query, which will result in this:
select a.deptcode, a.rollno, a.name
from
(select s.deptcode, s.name, s.rollno, sum(c.marks) as total from course c, students s where s.rollno = c.crs_rollno group by s.rollno) a
join (select deptcode, max(total) max_total from (select s.deptcode, s.name, s.rollno, sum(c.marks) as total from course c, students s where s.rollno = c.crs_rollno group by s.rollno) a_ group by deptcode) b
on a.deptcode = b.deptcode and a.total = b.max_total
Which I'm sure it is easily improvable in performance by someone more skilled then me...
If you (and anybody else) want to try it the way I did, here is the schema:
create table depts ( deptcode int primary key auto_increment, deptname varchar(20) );
create table students ( rollno int primary key auto_increment, name varchar(20) not null, deptcode int, foreign key (deptcode) references depts(deptcode) );
create table course ( crs_rollno int, crs_name varchar(20), marks int, foreign key (crs_rollno) references students(rollno) );
And here all the entries I inserted:
insert into depts (deptname) values ("Computer Science"),("Biology"),("Fine Arts");
insert into students (name,deptcode) values ("Turing",1),("Jobs",1),("Tanenbaum",1),("Darwin",2),("Mendel",2),("Bernard",2),("Picasso",3),("Monet",3),("Van Gogh",3);
insert into course (crs_rollno,crs_name,marks) values
(1,"Algorithms",25),(1,"Database",28),(1,"Programming",29),(1,"Calculus",30),
(2,"Algorithms",24),(2,"Database",22),(2,"Programming",28),(2,"Calculus",19),
(3,"Algorithms",21),(3,"Database",27),(3,"Programming",23),(3,"Calculus",26),
(4,"Zoology",22),(4,"Botanics",28),(4,"Chemistry",30),(4,"Anatomy",25),(4,"Pharmacology",27),
(5,"Zoology",29),(5,"Botanics",27),(5,"Chemistry",26),(5,"Anatomy",25),(5,"Pharmacology",24),
(6,"Zoology",18),(6,"Botanics",19),(6,"Chemistry",22),(6,"Anatomy",23),(6,"Pharmacology",24),
(7,"Sculpture",26),(7,"History",25),(7,"Painting",30),
(8,"Sculpture",29),(8,"History",24),(8,"Painting",30),
(9,"Sculpture",21),(9,"History",19),(9,"Painting",25) ;
Those inserts will load these data:
select * from depts;
+----------+------------------+
| deptcode | deptname |
+----------+------------------+
| 1 | Computer Science |
| 2 | Biology |
| 3 | Fine Arts |
+----------+------------------+
select * from students;
+--------+-----------+----------+
| rollno | name | deptcode |
+--------+-----------+----------+
| 1 | Turing | 1 |
| 2 | Jobs | 1 |
| 3 | Tanenbaum | 1 |
| 4 | Darwin | 2 |
| 5 | Mendel | 2 |
| 6 | Bernard | 2 |
| 7 | Picasso | 3 |
| 8 | Monet | 3 |
| 9 | Van Gogh | 3 |
+--------+-----------+----------+
select * from course;
+------------+--------------+-------+
| crs_rollno | crs_name | marks |
+------------+--------------+-------+
| 1 | Algorithms | 25 |
| 1 | Database | 28 |
| 1 | Programming | 29 |
| 1 | Calculus | 30 |
| 2 | Algorithms | 24 |
| 2 | Database | 22 |
| 2 | Programming | 28 |
| 2 | Calculus | 19 |
| 3 | Algorithms | 21 |
| 3 | Database | 27 |
| 3 | Programming | 23 |
| 3 | Calculus | 26 |
| 4 | Zoology | 22 |
| 4 | Botanics | 28 |
| 4 | Chemistry | 30 |
| 4 | Anatomy | 25 |
| 4 | Pharmacology | 27 |
| 5 | Zoology | 29 |
| 5 | Botanics | 27 |
| 5 | Chemistry | 26 |
| 5 | Anatomy | 25 |
| 5 | Pharmacology | 24 |
| 6 | Zoology | 18 |
| 6 | Botanics | 19 |
| 6 | Chemistry | 22 |
| 6 | Anatomy | 23 |
| 6 | Pharmacology | 24 |
| 7 | Sculpture | 26 |
| 7 | History | 25 |
| 7 | Painting | 30 |
| 8 | Sculpture | 29 |
| 8 | History | 24 |
| 8 | Painting | 30 |
| 9 | Sculpture | 21 |
| 9 | History | 19 |
| 9 | Painting | 25 |
+------------+--------------+-------+
I take chance to point out that this database is badly designed. This becomes evident with course table. For these reasons:
The name is singular
This table does not represent courses, but rather exams or scores
crs_name should be a foreign key referencing the primary key of another table (that would actually represent the courses)
There is no constrains to limit the marks to a range and to avoid a student to take twice the same exam
I find more logical to associate courses to departments, instead of student to departments (this way also would make these queries easier)
I tell you this because I understood you are learning from a book, so unless the book at one point says "this database is poorly designed", do not take this exercise as example to design your own!
Anyway, if you manually resolve the query with my data you will come to this results:
+----------+--------+---------+
| deptcode | rollno | name |
+----------+--------+---------+
| 1 | 1 | Turing |
| 2 | 6 | Bernard |
| 3 | 8 | Monet |
+----------+--------+---------+
As further reference, here the contents of the views I needed to define:
select * from total_marks;
+----------+-----------+--------+-------+
| deptcode | name | rollno | total |
+----------+-----------+--------+-------+
| 1 | Turing | 1 | 112 |
| 1 | Jobs | 2 | 93 |
| 1 | Tanenbaum | 3 | 97 |
| 2 | Darwin | 4 | 132 |
| 2 | Mendel | 5 | 131 |
| 2 | Bernard | 6 | 136 |
| 3 | Picasso | 7 | 81 |
| 3 | Monet | 8 | 83 |
| 3 | Van Gogh | 9 | 65 |
+----------+-----------+--------+-------+
select * from dept_max;
+----------+-----------+
| deptcode | max_total |
+----------+-----------+
| 1 | 112 |
| 2 | 136 |
| 3 | 83 |
+----------+-----------+
Hope I helped!
Try the following query
select a.name, b.deptname,c.marks
from students a
, crs_regd b
, depts c
where a.rollno = b.crs_rollno
and a.deptcode = c.deptcode
and(c.deptname,b.marks) in (select do.deptname, max(x.marks)
from students so
inner join depts do
on do.deptcode=so.deptcode
inner join (select s.name as name
, d.deptname as deptname
, sum(c.marks) as marks
from students s
inner join crs_regd c
on s.rollno=c.crs_rollno
inner join depts d
on d.deptcode=s.deptcode
group by s.name,d.deptname) x
on x.name=so.name
and x.deptname=do.deptname
group by do.deptname
)
Inner/Sub query will fetch the course name and max marks and the outer query gets the corresponding name of the student.
try and let know if you got the desired result
Dense_Rank() function would be helpful in this scenario:
SELECT subquery.*
FROM (SELECT Student_Total_Marks.rollno,
Student_Total_Marks.name,
Student_Total_Marks.deptcode, depts.deptname,
rank() over (partition by deptcode order by total_marks desc) Student_Rank
FROM (SELECT Stud.rollno,
Stud.name,
Stud.deptcode,
sum(course.marks) total_marks
FROM students stud inner join course course on stud.rollno = course.crs_rollno
GROUP BY stud.rollno,Stud.name,Stud.deptcode) Student_Total_Marks,
dept dept
WHERE Student_Total_Marks.deptcode = dept.deptname
GROUP BY Student_Total_Marks.deptcode) subquery
WHERE suquery.student_rank = 1
I am trying to select multiple columns from a table, but I want to select top certain number of records based on one column. I tried this :
select roll_no ,marks as Percentage
from database
where marks in (select top (3) *
from database
where subject = ''
order by marks desc) order by percentage desc
and I am getting the error:
Only one expression can be specified in the select list when the
sub-query is not introduced with EXISTS or more than specified number
of records.
I also tried :
select roll_no ,marks as Percentage
from database
where marks in (select top (3) marks
from database
where subject = ''
order by marks desc) order by percentage desc
which returns the right result for some subjects but for others..it is displaying top marks from other subjects as well.
eg :
+---------+-------+
| roll_no | marks |
+---------+-------+
|10003 | 87 |
|10006 | 72 |
|10003 | 72 |
|10002 | 67 |
|10004 | 67 |
+---------+-------+
How to frame the query correctly?
sample data :
+---------+-------+---------+
| roll_no | marks |subject |
+---------+-------+---------+
|10001 | 45 | Maths |
|10001 | 72 | Science |
|10001 | 64 | English |
|10002 | 52 | Maths |
|10002 | 35 | Science |
|10002 | 75 | English |
|10003 | 52 | Maths |
|10003 | 35 | Science |
|10003 | 75 | English |
|10004 | 52 | Maths |
|10004 | 35 | Science |
|10004 | 75 | English |
+---------+-------+---------+
If I'm right and you are looking for the best 3 marks for each subject, then you can get it with the following:
DECLARE #SelectedSubject VARCHAR(50) = 'Maths'
;WITH FilteredSubjectMarks AS
(
SELECT
D.Subject,
D.Roll_no,
D.Marks,
MarksRanking = DENSE_RANK() OVER (ORDER BY D.Marks DESC)
FROM
[Database] AS D
WHERE
D.Subject = #SelectedSubject
)
SELECT
F.*
FROM
FilteredSubjectMarks AS F
WHERE
F.MarksRanking <= 3
You can use window functions to rank your marks column (specifically dense_rank, which allows duplicate rankings whilst retaining sequential numbering) and then return all rows with a rank of 3 or less:
declare #t table(roll_no int identity(1,1),marks int);
insert into #t(marks) values(2),(4),(5),(8),(6),(1),(3),(2),(1),(8);
with t as
(
select roll_no
,marks
,dense_rank() over (order by marks desc) as r
from #t
)
select *
from t
where r <= 3;
Output:
+---------+-------+---+
| roll_no | marks | r |
+---------+-------+---+
| 4 | 8 | 1 |
| 10 | 6 | 1 |
| 5 | 6 | 2 |
| 3 | 5 | 3 |
+---------+-------+---+
I have a sample table of doctor visits by ID. I'm looking to rank the problems by age, partitioned by ID so I can do some statistic calculations on the 2nd and 3rd visit of the same problem by ID. Please Note: I have a larger dataset so i'm looking for something that will handle that.
So far I have
SELECT
ID, Age, Problem, COUNT(Problem) AS cnt,
RANK() OVER (PARTITION BY id ORDER BY Problem, Age ASC) AS rnk
FROM
#Test1
GROUP BY
ID, Problem, Age
ORDER BY
Age ASC
The code runs but the rank is not properly calculated. Please help.
As I understand, you need partition by ID and Problem:
CREATE TABLE #Test1 (ID int, Problem nvarchar(20), Age int)
INSERT INTO #Test1
VALUES
(1,'Arm',50),
(1,'Arm',52),
(1,'Foot',54),
(1,'Tongue',55),
(1,'Arm',59),
(2,'Toe',60),
(2,'Toe',60),
(2,'Arm',61),
(3,'Tooth',75),
(3,'Tooth',76),
(3,'Knee',78)
SELECT
ID,
Age,
Problem,
COUNT(*) OVER (PARTITION BY ID, Problem, Age) as cnt,
RANK() OVER (PARTITION BY ID, Problem ORDER BY Age) as rnk
FROM #Test1 AS t
ORDER BY t.Age
DROP TABLE #Test1
In this solution you will get the same rank = 1 for data (2,'Toe',60). To enumerate them, replace RANK with ROW_NUMBER
I believe you want row_number() instead of rank():
select
id
, Age
, Problem
, cnt = count(*) over (partition by id, Problem)
, rnk = row_number() over (partition by id, Problem order by Age)
from t
order by id, Age, Problem
test setup: http://rextester.com/DUWG50873
returns:
+----+-----+---------+-----+-----+
| id | Age | Problem | cnt | rnk |
+----+-----+---------+-----+-----+
| 1 | 50 | Arm | 3 | 1 |
| 1 | 52 | Arm | 3 | 2 |
| 1 | 54 | Foot | 1 | 1 |
| 1 | 55 | Tongue | 1 | 1 |
| 1 | 59 | Arm | 3 | 3 |
| 2 | 60 | Toe | 2 | 1 |
| 2 | 60 | Toe | 2 | 2 |
| 2 | 61 | Arm | 1 | 1 |
| 3 | 75 | Tooth | 2 | 1 |
| 3 | 76 | Tooth | 2 | 2 |
| 3 | 78 | Knee | 1 | 1 |
+----+-----+---------+-----+-----+
I would like to filter my table by MIN() function but still keep columns which cant be grouped.
I have table:
+----+----------+----------------------+
| ID | distance | geom |
+----+----------+----------------------+
| 1 | 2 | DSDGSAsd23423DSFF |
| 2 | 11.2 | SXSADVERG678BNDVS4 |
| 2 | 2 | XCZFETEFD567687SDF |
| 3 | 24 | SADASDSVG3423FD |
| 3 | 10 | SDFSDFSDF343DFDGF |
| 4 | 34 | SFDHGHJ546GHJHJHJ |
| 5 | 22 | SDFSGTHHGHGFHUKJYU45 |
| 6 | 78 | SDFDGDHKIKUI45 |
| 6 | 15 | DSGDHHJGHJKHGKHJKJ65 |
+----+----------+----------------------+
This is what I would like to achieve:
+----+----------+----------------------+
| ID | distance | geom |
+----+----------+----------------------+
| 1 | 2 | DSDGSAsd23423DSFF |
| 2 | 2 | XCZFETEFD567687SDF |
| 3 | 10 | SDFSDFSDF343DFDGF |
| 4 | 34 | SFDHGHJ546GHJHJHJ |
| 5 | 22 | SDFSGTHHGHGFHUKJYU45 |
| 6 | 15 | DSGDHHJGHJKHGKHJKJ65 |
+----+----------+----------------------+
it is possible when I use MIN() on distance column and grouping by ID but then I loose my geom which is essential.
The query looks like this:
SELECT "ID", MIN(distance) AS distance FROM somefile GROUP BY "ID"
the result is:
+----+----------+
| ID | distance |
+----+----------+
| 1 | 2 |
| 2 | 2 |
| 3 | 10 |
| 4 | 34 |
| 5 | 22 |
| 6 | 15 |
+----+----------+
but this is not what I want.
Any suggestions?
One common approach to this is to find the minimum values in a derived table that you join with:
SELECT somefile."ID", somefile.distance, somefile.geom
FROM somefile
JOIN (
SELECT "ID", MIN(distance) AS distance FROM somefile GROUP BY "ID"
) t ON t.distance = somefile.distance AND t.ID = somefile.ID;
Sample SQL Fiddle
You need a window function to do this:
SELECT "ID", distance, geom
FROM (
SELECT "ID", distance, geom, rank() OVER (PARTITION BY "ID" ORDER BY distance) AS rnk
FROM somefile) sub
WHERE rnk = 1;
This effectively orders the entire set of rows first by the "ID" value, then by the distance and returns the record for each "ID" where the distance is minimal - no need to do a GROUP BY.
select a.*,b.geom from
(SELECT ID, MIN(distance) AS distance FROM somefile GROUP BY ID) as a
inner join somefile as b on a.id=b.id and a.distance=b.distance
You can use "distinct on" clause of the PostgreSQL.
select distinct on(id) id, distance, geom
from table_name
order by distance;
I think this is what you are exactly looking for.
For more details on how "distinct on" works, refer the documentation and the example.
But, remember, using "distinct on" does not comply to SQL standards.