I have there different tables lets say A ,B ,C.
From table A the query I am using is
select a.status, a.resolution, a.ID
from A a ;
From table B I have to fetch B.destID when A.ID matches
For that I am using
select b.destID
from B b
where b.ID = A.ID ;
if b.destID exists then
select newstatus
from C
where C.id = B.destID
else
select newstatus
from C
where C.id = A.ID
Can somebody help me in combining all these three queries into one?
Any help is appreciated.. Thanks in advance
Sure:
select a.status,a.resolution,
Coalesce(c2.newstatus, c1.newstatus) newStatus
from A Left Join B On B.ID = A.ID
Left Join C c1 On c1.id = A.Id
Left Join C c2 On c2.id = B.destID
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
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);
I would like to do something like this but can't get it to work:
SELECT A.*,B.*,C.* FROM tableA A LEFT JOIN
B ON A.ID = B.ID
C ON A.ID = C.ID
I.e. I need to use a field from the first table for all joins as tableB and tableC don't
has any fields to link them together.
Can this be done?
you missed a join !
SELECT A.*,B.*,C.* FROM tableA A
LEFT JOIN
B ON A.ID = B.ID
left join
C ON A.ID = C.ID
Try this one -
SELECT *
FROM dbo.tableA A
LEFT JOIN dbo.B ON A.ID = B.ID
LEFT JOIN dbo.C ON A.ID = C.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.
i have four tables which are related like this:
TABLE A: 1 to many with TABLE B
TABLE B: 1 to many with TABLE C
TABLE D: many to 1 with TABLE B
I would like to create a result set which contains no duplicates.
SELECT A.f1
A.f2
B.f1
C.f1
D.f1
from A LEFT JOIN (B INNER JOIN D on D.fk_b = B.id) on A.id = B.fk_a
LEFT JOIN C on C.fk_b = B.id
Some but not all records are duplicated. Only the records from TABLE D which have the same FK to TABLE B.
If there are 2 the same D.fk_B fields then i would like to select only the first one. My INNER JOIN would become something like:
B INNER JOIN TOP 1 D on.....
But that's not possible?
Thank you!
Assuming that the structure in question is near the one shown bellow,
The following SELECT statement will show you just the primary keys, briefly giving an idea about what data is being returned.
SELECT
A.id AS `A_id`,
B.id AS `B_id`,
COALESCE(C.id, 0) AS `C_id`,
COALESCE(
(SELECT D.id FROM D WHERE D.fk_b = B.id LIMIT 1), 0
) AS `D_id`
FROM B
INNER JOIN A ON (B.fk_a = A.id)
LEFT JOIN C ON (B.id = C.fk_b);
Now the select you've asked for:
SELECT
A.f1 AS `A_f1`,
A.f2 AS `A_f2`,
B.f1 AS `B_f1`,
COALESCE(C.f1, '-') AS `C_f1`,
COALESCE(
(SELECT D.f1 FROM D WHERE D.fk_b = B.id LIMIT 1), '-'
) AS `D_f1`
FROM B
INNER JOIN A ON (B.fk_a = A.id)
LEFT JOIN C ON (B.id = C.fk_b);
Code above was tested and worked fine on MySQL 5.6
It appears that you have cartesian join.
You could try just putting DISTINCT infront of you column definition or you could so subqueries to link the tables together.
Try
SELECT DISTINCT A.f1
A.f2
B.f1
C.f1
D.f1
from A LEFT JOIN (B INNER JOIN D on D.fk_b = B.id) on A.id = B.fk_a
LEFT JOIN C on C.fk_b = B.id
You can do this:
B INNER JOIN TOP 1 D on.....
Like this
B INNER JOIN (SELECT TOP 1 fields from table) D ON ...
Try this:
SELECT DISTINCT A.f1
A.f2
B.f1
C.f1
D.f1
from A
LEFT JOIN (B INNER JOIN (SELECT DISTINCT fk_b FROM D) D on D.fk_b = B.id)
on A.id = B.fk_a
LEFT JOIN C on C.fk_b = B.id