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)
Related
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.
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.
So I have two tables (A and B) that have a relation of n-n.
So there is a third table (C) that is used to connect both tables.
Table A and B both have an Id and a name.
Table C has IDA, IDB and an Order, the number that is used to sort and that is user given.
My issue is that I need to migrate table C since I just added that order column and so I need to give every line an ordering number, according to the B name.
So if table A has:
Id Name
1 A
2 B
3 C
And Table B has:
Id Name
1 J
2 L
3 M
And table C has:
IdA IdB Order
1 2 0
1 1 0
1 3 0
2 1 0
2 3 0
I need a query that updates table C to be more like:
IdA IdB Order
1 2 2
1 1 1
1 3 3
2 1 1
2 3 2
I have a query that can basically do what i want but it leaves me with "gaps"
reading my results above i get:
IdA IdB Order
1 2 2
1 1 1
1 3 3
2 1 1
2 3 3
I think this should work for what you need:
With ToUpdate As
(
Select C.*,
Row_Number() Over (Partition By C.IdA Order By B.Name) As NewOrder
From C
Join B On B.Id = C.IdB
)
Update C
Set "Order" = U.NewOrder
From ToUpdate U
Where U.IdA = C.IdA
And U.IdB = C.IdB
(In full disclosure, I'm not terribly familiar with postgres, but I think this should be valid).
I have following tables in APEX A and B.
A has columns:
ID_A;
VALUE;
B has columns:
ID_C_FK;
ID_A_FK
I want to update the VALUE column in table A in rows where ID_A equals ID_A_FK in selected rows from table B where ID_C_FK equal x
For example: A has rows (
ID_A value
------------
1 1
2 1
3 0
4 0
5 0
Table B has rows
ID_C_FK ID_A_FK
------------------
8 4
9 4
9 5
I want to update VALUE in table A only for those rows that have ID_A in rows selected from B and condition to select rows from B is that ID_C_FK equals x = 9; and as a result, table A should end up having rows:
ID_A value
------------
1 1
2 1
3 0
4 1
5 1
How to write such update in PL/SQL?
Thank you for considering my request.
I think this is what you want:
update a
set value = 1
where exists (select 1
from b
where b.id_a_fk = a.id_a and b.id_c_fk = 9
);