SQL statement with pagination and sorting (join tables) - sql

I have two tables (Books, Authors) with ManyToMany relationship. I need SQL statement to retrieve books with authors, sorted by authors/books. Important thing is that I must retrieve them with pagination (offset ... fetch in sql).
One of the problem that when I join tables there are duplicates in results (of course) and offset/fetch can't be used for this results. Another problem the results must be sorted (not subpages but all books of course).
I have one idea: (it retrieves books sorted by author name and include pagination)
select b.id, b.title, a.name from Books b inner join Books_Authors ba
on ba.bookID = b.id inner join Authors a
on ba.authorID = a.id
where a.name in (select name from Authors order by name offset 9 rows fetch next 3 rows only)
order by a.name
But I think it's not efficient way.


Something like this?
select * from
(
select tmp1.*, ROW_NUMBER() over(partition by b.title, a.name order by b.id, a.id) rang2
from
(
select a.id, b.id, b.title, a.name, ROW_NUMBER() over(partition by b.title, a.name order by b.id, a.id) rang
from Books b inner join Books_Authors ba on ba.bookID = b.id
inner join Authors a on ba.authorID = a.id
) tmp1 where rang=1
) tmp2
where rang2 between 3 and 9
order by title, name


table1
sno exam questions time_duration
1 unit test 1 10
2 mock 1 2 10
3 mock2 5 10
4 mock3 6 6
table2
qid answer user_attempt_option
1 1 1
2 2 3
2 3 4
3 4 1
3 1 2
3 2 3
3 3 1

Related

Select all items having silmutaneously 2different values at the same column

I want to run an sql query and find all the books that have type="adventure" AND type="drama".
AND does not allow searching at the same time 2 different values of the same column.
My tables are like this
Books
Bid Bname Author
1 Sql loren
2 Monster Mike
3 Minnie Michel
----------
Copies
Cid Bid Type
1 1 Science
2 1 Teaching
3 2 Adventure
4 3 Romance
5 3 Drama
6 3 Adventure
The result I want:
Bid Title
3 Minnie
The tables can't change

There are several ways to do it, here is one using two exists conditions. Bottom line is that you have to check copies table twice.
SELECT * FROM books b
WHERE EXISTS
(
SELECT * FROM copies c1
WHERE b.bid = c1.bid
AND c1.type='adventure'
)
AND EXISTS
(
SELECT * FROM copies c2
WHERE b.bid = c2.bid
AND c2.type='drama'
)

You can achieve with JOIN, here is the DEMO. And you can use EXISTS as per #NenadZivkovic answer.
select
b.Bid,
Bname as Title
from books b
join Copies c
on b.Bid = c.Bid
and c.Type ='Drama'
join Copies c1
on c.Bid = c1.Bid
and c1.Type = 'Adventure'
group by
b.Bid,
Bname
order by
b.Bid

Join one row only over three tables

(My question has been asked a lot of times with two tables involved, and has been answered here, here and here. But I can't figure out how to do the same with three tables involved.)
I have three tables, A, B and C, where A has many B and B has many C. I want to join these tables and select zero or one rows per A, which one should be based on a condition in C.
Example, assume that:
SELECT
a.aId
,b.bId
,c.cId
FROM
a
INNER JOIN b ON b.aId=a.aId
INNER JOIN c ON c.bId=b.bId
WHERE
c.someColumn='foo'
...yields the following result:
aId bId cId
=== === ===
1 11 101
1 12 102
1 12 103
2 21 201
2 21 203
2 22 202
...then I would like to, for instance, retrieve two distinct A-rows, the ones with highest cId.
aId bId cId
=== === ===
1 12 103
2 21 203

You can use ROW_NUMBER:
WITH Cte AS (
SELECT
a.aId,
b.bId,
c.cId,
rn = ROW_NUMBER() OVER (PARTITION BY a.aId ORDER BY c.cId DESC)
FROM a
INNER JOIN b
ON b.aId = a.aId
INNER JOIN c
ON c.bId = b.bId
WHERE c.someColumn = 'foo'
)
SELECT
aId, bId, cId
FROM Cte
WHERE rn = 1

Is it possible to left join two tables and have the right table supply each row no more than once?

Given this table structure:
Table A
ID AGE EDUCATION
1 23 3
2 25 6
3 22 5
Table B
ID AGE EDUCATION
1 26 4
2 24 6
3 21 3
I want to find all matches between the two tables where the age is within 2 and the education is within 2. However, I do not want to select any row from TableB more than once. Each row in B should be selected 0 or 1 times and each row in A should be selected one or more times (standard left join).
SELECT *
FROM TableA as A LEFT JOIN TableB as B ON
abs(A.age - B.age) <= 2 AND
abs(A.education - B.education) <= 2
A.ID A.AGE A.EDUCATION B.ID B.AGE B.EDUCATION
1 23 3 3 21 3
2 25 6 1 26 4
2 25 6 2 24 6
3 22 5 2 24 6
3 22 5 3 21 3
As you can see, the last two rows in the output have duplicated B.ID of 2 and 3 when compared to the entire result set. I'd like those rows to return as a single null match with A.ID = 3 since they were both matched to previous A values.
Desired output:
(note that for A.ID = 3, there is no match in B because all rows in B have already been joined to rows in A.)
A.ID A.AGE A.EDUCATION B.ID B.AGE B.EDUCATION
1 23 3 3 21 3
2 25 6 1 26 4
2 25 6 2 24 6
3 22 5 null null null
I can do this with a short program, but I'd like to solve the problem using a SQL query because it is not for me and I will not have the luxury of ever seeing the data or manipulating the environment.
Any ideas? Thanks

As #Joel Coehoorn said earlier, there has to be a mechanism that selects which pairs of (a,b) with the same (b) are filtered out from the output. SQL is not great on allowing you to select ONE row when multiple match, so a pivot query needs to be created, where you filter out the records you don't want. In this case, filtering can be done by reducing all of match IDs of B as a smallest (or largest, it doesn't really matter), using any function that will return one value from a set, it's just min() and max() are most convenient to use. Once you reduced the result to know which (a,b) pairs you care about, then you join against that result, to pull out the rest of the table data.
select a.id a_id, a.age a_age, a.education a_e,
b.id b_id, b.age b_age, b.education b_e
from a left join
(
SELECT
a.id a_id, min(b.id) b_id from a,b where
abs(A.age - B.age) <= 2 AND
abs(A.education - B.education) <= 2
group by a.id
) g on a.id = g.a_id
left join b on b.id = g.b_id;

To my knowledge something like this is not possible with a simple select statement and joins because you need to know what has already been selected in order to eliminate duplicates.
You can however try something a little more like this:
DECLARE #JoinResults TABLE
(A_ID INT, A_Age INT, A_Education INT, B_ID INT, B_Age INT, B_Education INT)
INSERT INTO #JoinResults (A_ID, A_Age, A_Education)
SELECT ID, AGE, EDUCATION
FROM TableA
DECLARE #i INT
SET #i = 1
--Assume that A_ID is incremental and no values missed
WHILE (#i < (SELECT Max(A_ID) FROM #JoinResults
BEGIN
UPDATE #JoinResult
SET B_ID = SQ.ID,
B_Age = SQ.AGE,
B_Education = SQ.Education
FROM (
SELECT ID, AGE, EDUCATION
FROM TableB b
WHERE (
abs((SELECT A_Age FROM #JoinResult WHERE A_Id = #i) - AGE) <=2
AND abs((SELECT A_Education FROM #JoinResult WHERE A_Id = #i) - EDUCATION) <=2
) AND (SELECT B_ID FROM #JoinResults WHERE B_ID = b.id) IS NULL
) AS SQ
SET #i = #i + 1
END
SELECT #JoinResults
NOTE: I do not currently have access to a database so this is untested and I am weary of 2 potential issues with it
I am not sure how the update will react if there are no results
I am unsure if the IS NULL check is correct to eliminate the duplicates.
If these issues do arise let me know and I can help troubleshoot.

In SQL-Server, you can use the CROSS APPLY syntax:
SELECT
a.id, a.age, a.education,
b.id AS b_id, b.age AS b_age, b.education AS b_education
FROM tableB AS b
CROSS APPLY
( SELECT TOP (1) a.*
FROM tableA AS a
WHERE ABS(a.age - b.age) <= 2
AND ABS(a.education - b.education) <= 2
ORDER BY a.id -- your choice here
) AS a ;
Depending on the order you choose in the subquery, different rows from tableA will be selected.
Edit (after your update): But the above query will not show rows from A that have no matching rows in B or even some that have but not been selected.
It could also be done with window functions but Access does not have them. Here is a query that I think will work in Access:
SELECT
a.id, a.age, a.education,
s.id AS s_id, s.age AS b_age, s.education AS b_education
FROM tableB AS a
LEFT JOIN
( SELECT
b.id, b.age, b.education, MIN(a.id) AS a_id
FROM tableB AS b
JOIN tableA AS a
ON ABS(a.age - b.age) <= 2
AND ABS(a.education - b.education) <= 2
GROUP BY b.id, b.age, b.education
) AS s
ON a.id = s.a_id ;
I'm not sure if Access allows such a subquery but if it doesn't, you can define it as a "Query" and then use it in another.

Use SELECT DISTINCT
SELECT DISTINCT A.id, A.age, A.education, B.age, B.education
FROM TableA as A LEFT JOIN TableB as B ON
abs(A.age - B.age) <= 2 AND
abs(A.education - B.education) <= 2

Get Count for each Joined Record

I have 2 tables which I'd like to join and..
A:
ID Otherfields..
1 ...
2
3
4
B:
ID aId Otherfields..
1 1 ...
2 1
3 2
4 1
So I'm perfectly capable of joining them by a.Id but how do get I get the count for the matches in Table B, like:
a.id count(b)
1 3
2 1
I figured it must be something with count() over() but cannot recall the exact use.
Thanks!

You can simply do this:
SELECT
A.ID, COUNT(b.ID)
FROM A
INNER JOIN B ON A.Id = b.aID
GROUP BY A.ID

You can have
SELECT A.ID, COUNT(b.ID)
FROM A
LEFT JOIN B ON A.Id = b.aID
GROUP BY A.ID
This will give you all a.IDs that don't exist in b.ID and hence show their count as 0.
E.g.,
ID Count
1 3
2 1
3 0
4 0

sql query for 3 tables

i have 3 tables (A,B,C)
Table A -
ID Name
1 Sam
2 Manuel
3 Jane
Table B
ID Tab_A_ID Name
1 1 Meer
2 1 Kutti
3 2 Mikaro
Table C
ID Tab_B_ID Price
1 1 255.11
2 1 30.52
3 3 125.22
I need a query that shall pick up the top price for TableA-Name from TableC. So only 1 top price for 1 nae record.
e.g.-
Sam - 255.11
Manuel - 125.22
How can i get this?

To get the max price per entry in A:
SELECT a.Name,
MAX(c.price)
FROM a
INNER JOIN b
ON a.id = b.tab_a_id
INNER JOIN c
ON b.id = c.tab_b_id
GROUP BY a.id, a.name
To get the max price per entry A per entry B:
SELECT a.Name,
b.Name
MAX(c.price)
FROM a
INNER JOIN b
ON a.id = b.tab_a_id
INNER JOIN c
ON b.id = c.tab_b_id
GROUP BY a.id, b.id, a.name, b.name
Note that entries in A without corresponding entires in B or entries in B without corresponding entries in C will not appear in the result. Use LEFT JOIN if you want to include these in the result.