Here is the Exercise we were given to practice our SQL refresher
Get all rows from TableA. If a match is available in both TableB and TableC, include it. This means that if data is available in TableB or TableC, but not both, data from both willbe excluded and only TableA data will be show
This is currently my full syntax I am using at the current moment.
SELECT *
FROM dbo.TableA a
LEFT JOIN dbo.TableB b ON a.ID = b.ID
LEFT JOIN dbo.TableC c ON a.ID = b.ID AND b.ID = c.ID
WHERE a.ID <100;
go
And this is the corresponding output I am getting.
I am trying to change Column B record 2 into NULL as it does not match Column C. Is there anyway I can get something like this to work, if I try this in the syntax it throws an identifier can not be found.
LEFT JOIN dbo.TableB b
on a.ID = b.ID and TableC.ID = b.ID
Expecting
All From Table A
Rows from TableB that match TableA and TableC
Rows from TableC that match TableA and TableB
Figured out my logic was a bit wrong.
I decided to try and layout the tables differently to see if that works and it ended up getting to what I needed
select *
from dbo.TableB b
inner join dbo.TableC c
on b.ID = c.ID
right outer join dbo.TableA a
on b.ID = a.ID
where a.ID < 100;
go
Related
I have problem getting values from tables.
I need something like this
A.Id a1
B.Id b1
C.Id c1
B.Id b2
C.Id c2
C.Id c3
C.Id c4
Table A and B are joined together and also table B and C.
Table A can have one/zero or more values from table B. Same situation is for values from table C.
I need to perform left join on table A over table B and inside that left join on table B over table C.
I tried with left join from table A and B, but don't know how to perform left join inside that left join.
Is that possible? What would syntax for that look like?
edit:
Data would look like this
ZZN1 P1 NULL
ZZN1 P2 NAB1
ZZN2 P3 NAB2
ZZN2 P3 NAB3
No need to nest the left joins, you can simply flatten them and let your RDMBS handle the logic.
Sample schema:
a(id)
b(id, aid) -- aid is a foreign key to a(id)
c(id, bid) -- bid is a foreign key to b(id)
Query:
select a.id, b.id, c.id
from a
left join b on b.aid = a.id
left join c on c.bid = b.id
If the first left join does not succeed, then the second one cannot be performed either, since joining column b.id will be null. On the other hand, if the first left join succeeds, then the second one may, or may not succeed, depending if the relevant bid is available in c.
SELECT A.Name, B.Name , C.Name
FROM A
LEFT JOIN B ON A.id = B.id
LEFT JOIN C ON B.id = C.id
Can anyone help me figure out the correct WHERE clause for the following scenario:
select A.name
from tableA A, tableB B
where A.id = B.id
and
(
B.field = 5
OR
B.hasNoRowForJoinedID
)
I feel like I'm missing something really obvious here in how to accomplish this, but I can't for the life of me put my finger on it.
You are using an outdated SQL Syntax. To perform the LEFT OUTER JOIN based your your request above, you can do the following:
SELECT A.name
FROM A
LEFT OUTER JOIN B ON A.id = B.id
WHERE (B.field = 5 OR B.field IS NULL)
Use proper join syntax and not the outdated ones:
select A.name
from tableA A
left join tableB B on A.id = B.id and B.field = 5
I am not sure if this can be done with a single JOIN, but I basically have two tables with an ID column in common. To make it simple I'll say Table A just contains an ID while Table B contains an ID and Code. There is a 1:M relationship between Table A and Table B, however it's also possible an ID from Table A is not contained in Table B at all. I was hoping to have a query return every ID that exists in Table B within a particular code range, or does not exist in Table B at all.
I tried using a LEFT JOIN with something like:
SELECT A.id FROM A LEFT JOIN B ON A.id = B.id AND b.code BETWEEN '000' AND '123'
But, this still gives me the IDs that exist in Table B outside of the code range.
Use a left join, and filter the result to contain the codes in the range, and also the lines where there is no matching record in table B:
select
A.id
from
A
left join B on B.id = A.id
where
B.code between '000' and '123' or B.id is null
What about
SELECT id FROM A LEFT JOIN B ON A.id = B.id
WHERE b.code IS NULL OR b.code BETWEEN ' ' AND '123'
This is evidently correct syntax in SQL Server:
SELECT a.id, b.name
FROM Table1 a, Table2 b
WHERE a.id = b.fk1
So is this:
SELECT a.id, c.status
FROM Table1 a
JOIN Table3 c ON a.id = c.fk2
But this apparently isn't:
SELECT a.id, b.name, c.status
FROM Table1 a, Table2 b
JOIN Table3 c ON a.id = c.fk2
WHERE a.id = b.fk1
I would NOT normally want to construct a query in the third case's style (and really not the first case's either), but it would probably be the path of least resistence in editing some code that's already been written at my company. Somebody used the first form with five different tables, and I really need to work in a sixth table through a JOIN statement, without taking chances of messing up what they already have. Even though I could re-write their stuff outright if I need to, I would really like to know how to do something like in the third case.
Running the code exactly as-is in the examples, the third case gives me this error message:
The multi-part identifier "a.id" could not be bound.
What is syntactically breaking the third case? What simple fix could be applied? Thanks!
I, likewise, would not recommend doing this. But, you can just change the , to a cross join:
SELECT a.id, b.name, c.status
FROM Table1 a cross join Table2 b
JOIN Table3 c ON a.id = c.fk2
WHERE a.id = b.fk1
This code:
SELECT a.id, b.name, c.status
FROM Table1 a, Table2 b
JOIN Table3 c ON a.id = c.fk2
WHERE a.id = b.fk1
is doing a cross join on a and the result of an inner join on b and c. c cannot access any of the fields in a because the join is being performed on b. what you should do is change your query to:
SELECT a.id, b.name, c.status
FROM Table1 a
inner join Table2 b on a.id = b.fk1
inner JOIN Table3 c ON a.id = c.fk2
Say I have three tables in SQL server 2008 R2
SELECT a.*, b.*, c.*
FROM
Table_A a
RIGHT JOIN Table_B b ON a.id = b.id
LEFT JOIN Table_C c ON b.id = c.id
or
SELECT a.*, b.*, c.*
FROM
Table_A a
RIGHT JOIN Table_B b ON a.id = b.id
JOIN Table_C c ON b.id = c.id
also, does it matter if I use b.id or a.id on joining c?
i.e. instead of JOIN Table_C c ON b.id = c.id, use JOIN Table_C c ON a.id = c.id
Thank you!
If it doesn't change the semantics of the query, the database server can reorder the joins to run in whichever way it thinks is more efficient.
Usually, if you want to force a certain order, you can use inline view subqueries, as in
SELECT a.*, x.*
FROM
Table_A a
RIGHT JOIN
(
SELECT *, b.id as id2 FROM Table_B b
LEFT JOIN Table_C c ON b.id = c.id
) x
ON a.id = x.id2
According to the definitions:
JOIN
: Return rows when there is at least one match in both tables
LEFT JOIN Return all rows from the left table, even if there are no matches in the right table
RIGHT JOIN Return all rows from the right table, even if there are no matches in the left table
The first option would include all raws from the 1st Join on Tables a and b even if there are no matching ones in table c, while the second statement would show only raws which match ones in table c.
regarding the second question i guess it would make a difference, since the 1st join includes all ids from table b, even though there are no matching ones in table a, so once you change your Join creterium to a.id you will get a different set of ids than b.id.
Yes, you do need a LEFT JOIN after a RIGHT JOIN
See
http://sqlfiddle.com/#!3/2c079/5/0
http://sqlfiddle.com/#!3/2c079/6/0
If you don't, the (inner) JOIN at the end will cancel out the effect of your RIGHT JOIN.
That wouldn't make any sense to have a RIGHT JOIN if you don't care. And if you care, you will have to add a LEFT JOIN after it.