Table A: 1 1 1 2 2 3 3 3 4 4
Table B: 1 1 2 2 3 3 5 5 5
What will be the output if the two tables are inner joined?
My answer was 1 1 2 2 3 3 but the interviewer said it wrong :/
According to my knowledge, inner join means the common factors of two tables. What should be my approach to this question?
Answer will be :
1
1
1
1
1
1
2
2
2
2
3
3
3
3
3
3
db<>fiddle demo
Let me explain for 1:
There are three rows containing 1 in TableA and two rows with 1 in TableB, so the final output will have 3*2 = six 1. Similarly for the other values.
It depends entirely on what the query is. If you do:
select *
from a join
b
on 1=0;
You will get no rows.
If you do:
select *
from t1 join
t2
on 1=1;
You will generate a Cartesian product.
If you do:
select *
from a join
b
on a.col = 4 and b.col = 2;
You will get 4 rows with 4 2 repeated four times.
If you do:
select *
from a join
b
on b.col^2 = a.col^3 + 1;
You will get four rows each with 2 and 3.
And so on.
Your question doesn't have enough information.
Related
The table to find which rows contains same value on two different columns for 2 rows. Here is a small sample rows among 2k+ rows.
id left right
1 3 4
2 4 1
3 1 9
4 2 6
5 2 5
6 9 8
7 0 7
In the above case, I need to get row 1,2,3,6 as it contains 4 on two rows of two different columns i.e (id=1&2),1 on two rows of two different columns(id=1&3) and 9 on two rows of two different columns(id=3&6)
My thoughts:
I did thought many things for example cross join on left and right column, group by and count etc.
with Final as (With OuterTable as (WITH Alias AS (SELECT id as left_id , left FROM Test)
SELECT DISTINCT id, left_id FROM Alias
INNER JOIN Test ON Alias.left = Test.right)
SELECT id from OuterTable
UNION ALL
SELECT left_id from OuterTable)
SELECT DISTINCT * from Final;
It's messy, but it works.
You can do it with EXISTS:
SELECT t1.*
FROM tablename t1
WHERE EXISTS (
SELECT 1 FROM tablename t2
WHERE t1.id <> t2.id AND (t2.left = t1.right OR t1.left = t2.right)
)
See the demo.
Results:
id
left
right
1
3
4
2
4
1
3
1
9
6
9
8
I am currently having troubles with filtering my SQL records. I need something like what it results in the following concept: Table is
A B
1 1
1 3
2 1
2 2
2 3
2 4
3 1
3 2
I want to select value of A , where B=1 and B=2 And B=3 when same A .... result is
A
2
Please help
You can use aggregation:
select a
from mytable
where b in (1, 2, 3)
group by a
having count(*) = 3
This assumes no duplicates in the table - else, you need to change the having clause to:
having count(distinct b) = 3
Lets say I have the following table
a b c
-----------
1 1 5
1 2 3
4 1 2
1 2 4
4 2 10
And I want to delete all rows where none of the first n rows has the same value in a and b as that row.
So for example the resulting tables for various n's would be
n = 1
a b c
-----------
1 1 5
// No row other than the first has a 1 in a, and a 1 in b
n = 2
a b c
-----------
1 1 5
1 2 3
1 2 4
// The fourth row has the same values in a and b as the second, so it is not deleted. The first 2 rows of course match themselves so are not deleted
n = 3
a b c
-----------
1 1 5
1 2 3
4 1 2
1 2 4
// The fourth row has the same values in a and b as the second, so it is not deleted. The first 3 rows of course match themselves so are not deleted
n = 4
a b c
-----------
1 1 5
1 2 3
4 1 2
1 2 4
// The first 4 rows of course match themselves so are not deleted. The fifth row does not have the same value in both a and b as any of the first 4 rows, so is deleted.
I've been trying to work out how to do this using a not in or a not exists, but since I'm interested in two columns matching not just 1 or the whole record, I'm struggling.
Since you are not defining a specific order, the result is not completely defined, but depends on arbitrary choices of implementation regarding which rows are computed first in the limit clause. A different SQLite version for example may give you a different result. With that being said, I believe that you want the following query:
select t1.* from table1 t1,
(select distinct t2.a, t2.b from table1 t2 limit N) tabledist
where t1.a=tabledist.a and t1.b=tabledist.b;
where you should replace N with the desired number of rows
EDIT: So, to delete directly from the existing table you need something like:
with toremove(a, b, c) as
(select * from table1 tt
EXCEPT select t1.* from table1 t1,
(select distinct t2.a, t2.b from table1 t2 limit N) tabledist
where t1.a=tabledist.a and t1.b=tabledist.b)
delete from table1 where exists
(select * from toremove
where table1.a=toremove.a and table1.b=toremove.b and table1.c=toremove.c);
I have the following tables:
Table I:
etu | nr |
1 2
2 2
2 3
2 1
3 4
3 9
Table A:
etu | rsp | nr
2 8 2
2 7 3
2 3 1
3 2 4
3 6 9
Now what I want to have as a result table is
etu | nr | rsp
2.. 3 7
3.. 9 6
So etu and nr are linked together and if multiple equal etu entries are available only the one with the highest nr is taken and the rsp value is added in the result table. in addition if more etu entries are available in the table I there are .. added to the etu value.
Explain: For the 3 9 6 row: The last row on table I is 3 9 so 3 is the number that is looked for and 9 is the highest number for the 3 rows. So we take that and add the rsp value for that ( 6 ) and we add that to the result table. For the 2 row it is the same 2 3 being the highest 2 row in table I.
I got something like:
select x.etu, x.rsp, y.nr from(
select i.etu etu, max(i.nr) maxnr, a.rsp from i left join a on
i.etu=a.etu and i.nr=a.nr group by etu)t
inner join a x on x.etu=t.etu and x.nr=t.nr inner join y on y.etu=t.etu
and y.nr=t.nr
or
select i.etu, max(i.nr) a.rsp from i left join a on i.etu=a.etu and
i.nr=a.nr grounp by
None even get me close to get the results that I want less add the .. after the etu when having the right result.
The system is DB10.5 Windows.
Thank you for all your help in advance.
Viking
I would use a CTE here like this:
with tmp as (
select i.etu, max(i.nr) as nt, count(*) as cnt
from i
group by i.etu)
select case
when tmp.cnt = 1 then char(a.etu)
else concat(rtrim(char(a.etu)), '..')
end as etu,
a.nr,
a.rsp
from tmp
left outer join a
on a.etu = tmp.etu
and a.nr = tmp.nr
The CTE provides the information necessary to join with a to get the correct response, and append the .. as necessary.
I've got a simple problem that really has me stumped.
I have a master table Table X
Table X
ID
_________
1
2
3
4
5
I have a join table for Table X that allows records to be self joined. Let's call this JoinTableX
JoinTableX
RecordAID RecordBID
--------- --------
1 2 (So Record 1 from Table X has a link to Record 2 from Table X)
1 3
1 4
2 3
2 4
3 1
3 2
4 1
4 2
So how do I write a SQL query to show me all the records in JoinTableX that have a duplicate dependency on each other (example bove Table X Record 1 is linked to Table X Record 4 and Table X Record 4 is linked to Table X Record 1.
select *
from JoinTableX a
inner join JoinTableX b on a.RecordAID = b.RecordBID
and a.RecordBID = b.RecordAID
(SELECT RecordAID, RecordBID FROM JoinTableX)
INTERSECT
(SELECT RecordBID, RecordAID FROM JoinTableX)