How can I get the red section of the following Venn diagram in SQL
Thanks for your help!
I would think first of except:
select c.*
from c
except
select a.*
from a
except
select b.*
from b;
My next thought would be not exists:
select c.*
from t
where not exists (select 1 from a where a.id = c.id) and
not exists (select 1 from b where b.id = c.id);
Using Joins you can get any portion of Ven diagram, Somethink like below for your scenario.
select c.*
from TableC c
left join TableA a on a.id = c.id
left join TableB b on b.id = c.id
Where a.id is null and b.id is null -- Records which does not match in both tables
Well there is gonna be a bit of handwaving considering you are not giving actual table structures, but something like this:
Select c.name
From c
Where not exists (select 1 from b where b.id = c.id)
And not exists (select 1 from a where a.id = c.id);
You can use NOT IN (assuming id is the common attribute):
SELECT c.id FROM c
WHERE c.id NOT IN (SELECT a.id FROM a)
AND c.id NOT IN (SELECT b.id FROM b);
Related
I'm writing an SQL statement in PostgreSQL where I'm JOINing data from different tables that are each connected by foreign keys on their ids. Table b has a field a_id which relates to the id of table a and so on.
My problem is that I want to reuse a value from the joined table in a WHERE clause without having to do all the JOINs again, like this:
SELECT *
FROM a
INNER JOIN b ON b.a_id = a.id
INNER JOIN c ON c.b_id = b.id
WHERE a.id = 3
AND a.x =
(SELECT c.y
FROM a
INNER JOIN b ON b.a_id = a.id
INNER JOIN c ON c.b_id = b.id
WHERE a.id = 3
AND c.id = 5)
I bet there's a simpler solution for this snippet that I'm just not realising. I'll be glad if anybody can help me out.
I don't have a silver bullet answer which simplifies your query, but CTEs certainly could make it a bit easier on the eyes:
WITH cte AS (
SELECT *
FROM a
INNER JOIN b ON b.a_id = a.id
INNER JOIN c ON c.b_id = b.id
WHERE a.id = 3
)
SELECT *
FROM cte
WHERE x IN (SELECT y FROM cte WHERE c_id = 5);
My aliases or column names may be off, and you may need to tidy up the CTE a bit before it would actually work for you.
You can use window functions for this:
SELECT . . .
FROM (SELECT a.*, b.*, c.*, -- should list the columns explicitly
MAX(c.y) FILTER (WHERE c.id = 5) OVER () as y_5
FROM a INNER JOIN
b
ON b.a_id = a.id INNER JOIN
c
ON c.b_id = b.id
WHERE a.id = 3
) abc
WHERE abc.x = abc.y_5;
I hope the below-mentioned query will help you.
SELECT *
FROM a
INNER JOIN b ON b.a_id = a.id
INNER JOIN c ON c.b_id = b.id
WHERE a.id = 3 and c.id =5 and a.x = c.y
Given two tables, is there a name for the result of subtracting inner join from full outer join, both on the same condition? Is it a type of "join"? Thanks.
It is not a type of join in SQL. You can write it as:
select . . .
from a full join
b
on a.id = b.id
where a.id is null or b.id is null;
If you are looking for ids that are in only one table, it can be more efficient to do:
select a.id
from a
where not exists (select 1 from b where b.id = a.id)
union all
select b.id
from b
where not exists (select 1 from a where a.id = b.id);
I have tables a, b, c, and d whereby:
There are 0 or more b rows for each a row
There are 0 or more c rows for each a row
There are 0 or more d rows for each a row
If I try a query like the following:
SELECT a.id, SUM(b.debit), SUM(c.credit), SUM(d.other)
FROM a
LEFT JOIN b on a.id = b.a_id
LEFT JOIN c on a.id = c.a_id
LEFT JOIN d on a.id = d.a_id
GROUP BY a.id
I notice that I have created a cartesian product and therefore my sums are incorrect (much too large).
I see that there are other SO questions and answers, however I'm still not grasping how I can accomplish what I want to do in a single query. Is it possible in SQL to write a query which aggregates all of the following data:
SELECT a.id, SUM(b.debit)
FROM a
LEFT JOIN b on a.id = b.a_id
GROUP BY a.id
SELECT a.id, SUM(c.credit)
FROM a
LEFT JOIN c on a.id = c.a_id
GROUP BY a.id
SELECT a.id, SUM(d.other)
FROM a
LEFT JOIN d on a.id = d.a_id
GROUP BY a.id
in a single query?
Your analysis is correct. Unrelated JOIN create cartesian products.
You have to do the sums separately and then do a final addition. This is doable in one query and you have several options for that:
Sub-requests in your SELECT: SELECT a.id, (SELECT SUM(b.debit) FROM b WHERE b.a_id = a.id) + ...
CROSS APPLY with a similar query as the first bullet then SELECT a.id, b_sum + c_sum + d_sum
UNION ALL as you suggested with an outer SUM and GROUP BY on top of that.
LEFT JOIN to similar subqueries as above.
And probably more... The performance of the various solutions might be slightly different depending on how many rows in A you want to select.
SELECT a.ID, debit, credit, other
FROM a
LEFT JOIN (SELECT a_id, SUM(b.debit) as debit
FROM b
GROUP BY a_id) b ON a.ID = b.a_id
LEFT JOIN (SELECT a_id, SUM(b.credit) as credit
FROM c
GROUP BY a_id) c ON a.ID = c.a_id
LEFT JOIN (SELECT a_id, SUM(b.other) as other
FROM d
GROUP BY a_id) d ON a.ID = d.a_id
Can also be done with correlated subqueries:
SELECT a.id
, (SELECT SUM(debit) FROM b WHERE a.id = b.a_id)
, (SELECT SUM(credit) FROM c WHERE a.id = c.a_id)
, (SELECT SUM(other) FROM d WHERE a.id = d.a_id)
FROM a
I have table A, B and C
I want to return all entries in table A that do not exist in table B and of that list do not exist in table C.
select * from table_A as a
where not exists (select 1 from table_B as b
where a.id = b.id)
this gives me the first result of entries in A that are not in B. But now I want only those entries of this result that are also not in C.
I tried flavours of:
select * from table_A as a
where not exists (select 1 from table_B as b
where a.id = b.id)
AND
where not exists (select 1 from table_C as c
where a.id = c.id)
But that isnt the correct logic. If there is a way to store the results from the first query and then select * from that result that are not existent in table C. But I'm not sure how to do that. I appreciate the help.
Try this:
select * from (
select a.*, b.id as b_id, c.id as c_id
from table_A as a
left outer join table_B as b on a.id = b.id
left outer join table_C as c on c.id = a.id
) T
where b_id is null
and c_id is null
Another implementation is this:
select a1.*
from table_A as a1
inner join (
select a.id from table_A
except
select b.id from table_B
except
select c.id from table_c
) as a2 on a1.id = a2.id
Note the restrictions on the form of the sub-query as described here. The second implementation, by most succinctly and clearly describing the desired operation to SQL Server, is likely to be the most efficient.
You have two WHERE clauses in (the external part of) your second query. That is not valid SQL. If you remove it, it should work as expected:
select * from table_A as a
where not exists (select 1 from table_B as b
where a.id = b.id)
AND
not exists (select 1 from table_C as c -- WHERE removed
where a.id = c.id) ;
Tested in SQL-Fiddle (thnx #Alexander)
how about using LEFT JOIN
SELECT a.*
FROM TableA a
LEFT JOIN TableB b
ON a.ID = b.ID
LEFT JOIN TableC c
ON a.ID = c.ID
WHERE b.ID IS NULL AND
c.ID IS NULL
SQLFiddle Demo
One more option with NOT EXISTS operator
SELECT *
FROM dbo.test71 a
WHERE NOT EXISTS(
SELECT 1
FROM (SELECT b.ID
FROM dbo.test72 b
UNION ALL
SELECT c.ID
FROM dbo.test73 c) x
WHERE a.ID = x.ID
)
Demo on SQLFiddle
Option from #ypercube.Thank for the present;)
SELECT *
FROM dbo.test71 a
WHERE NOT EXISTS(
SELECT 1
FROM dbo.test72 b
WHERE a.ID = b.ID
UNION ALL
SELECT 1
FROM dbo.test73 c
WHERE a.ID = c.ID
);
Demo on SQLFiddle
I do not like "not exists" but if for some reason it seems to be more logical to you; then you can use a alias for your first query. Subsequently, you can re apply another "not exists" clause. Something like:
SELECT * FROM
( select * from tableA as a
where not exists (select 1 from tableB as b
where a.id = b.id) )
AS A_NOT_IN_B
WHERE NOT EXISTS (
SELECT 1 FROM tableC as c
WHERE c.id = A_NOT_IN_B.id
)
I have two tables with a 1:n relationship to my base table, both of which I want to LEFT JOIN.
-------------------------------
Table A Table B Table C
-------------------------------
|ID|DATA| |ID|DATA| |ID|DATA|
-------------------------------
1 A1 1 B1 1 C1
- - 1 C2
I'm using:
SELECT * FROM TableA a
LEFT JOIN TableB b
ON a.Id = b.Id
LEFT JOIN TableC c
ON a.Id = c.Id
But this is showing duplicates for TableB:
1 A1 B1 C1
1 A1 B1 C2
How can I write this join to ignore the duplicates? Such as:
1 A1 B1 C1
1 A1 null C2
I think you need to do logic to get what you want. You want for any multiple b.ids to eliminate them. You can identify them using row_number() and then use case logic to make subsequent values NULL:
select a.id, a.val,
(case when row_number() over (partition by b.id, b.seqnum order by b.id) = 1 then val
end) as bval
c.val as cval
from TableA a left join
(select b.*, row_number() over (partition by b.id order by b.id) as seqnum
from tableB b
) b
on a.id = b.id left join
tableC c
on a.id = c.id
I don't think you want a full join between B and C, because you will get multiple rows. If B has 2 rows for an id and C has 3, then you will get 6. I suspect that you just want 3. To achieve this, you want to do something like:
select *
from (select b.*, row_number() over (partition by b.id order by b.id) as seqnum
from TableB b
) b
on a.id = b.id full outer join
(select c.*, row_number() over (partition by c.id order by c.id) as seqnum
from TableC c
) c
on b.id = c.id and
b.seqnum = c.seqnum join
TableA a
on a.id = b.id and a.id = c.id
This is enumerating the "B" and "C" lists, and then joining them by position on the list. It uses a full outer join to get the full length of the longer list.
The last join references both tables so TableA can be used as a filter. Extra ids in B and C won't appear in the results.
Do you want to use distinct
SELECT distinct * FROM TableA a
LEFT JOIN TableB b
ON a.Id = b.Id
LEFT JOIN TableC c
ON a.Id = c.Id
Do it as a UNION, i.e.
SELECT TableA.ID, TableB.ID, TableC.Id
FROM TableA a
INNER JOIN TableB b ON a.Id = b.Id
LEFT JOIN TableC c ON a.Id = c.Id
UNION
SELECT TableA.ID, Null, TableC.Id
FROM TableA a
LEFT JOIN TableC c ON a.Id = c.Id
i.e. one SELECT to being back the first row and another to bring back the second row. It's a bit rough because I don't know anything about the data you are trying to read but the principle is sound. You may need to rework it a bit.