I want to get values from two tables like in the following example:
Suppose we have this two tables:
TableA (with link to tableB):
Id | Id_TableB | Name
---------------------
1 | 1 | Ralf
2 | NULL | Marta
TableB:
Id | Color
---------------------
1 | Blue
2 | Red
I would like to get values for Color if there is a link, NULL otherwise:
Result:
Id | Name | Color
-----------------------------
1 | Ralf| Blue
2 | Marta| NULL
Any ideas on how to solve this?
You need a left outer join .
SELECT t1.Id, t1.Name, t2.Color
from TableA t1 left outer join TableB t2
on t1.Id_TableB = t2.Id;
Please check the link that I have provided above. Its a simplified tutorial
select
a.Id,
a.Name,
b.Color
from
a
left outer join
b
on
a.Id_TableB = b.Id
group by
b.Id
The group by b.Id is necessary if you have a one-to-many relationship a->b.
You need to use a LEFT OUTER JOIN, which includes rows even when there are NULLs. Something like this:
SELECT *
FROM TableA a
LEFT OUTER JOIN TableB b on a.ID_TableB = b.ID
More info here:
http://msdn.microsoft.com/en-us/library/ms187518.aspx
Hope this helps,
John
just you have to use outer join for this....
select a.id,a.Name, b.Color from tableB as b
left join tableA as a on b.Id = a.id_tableB
and for this you can use in condition as well
you can try below query--
select a.id,a.Name, b.Color from tableB as b,tableA as a on b.Id(+) = a.id_tableB
Related
I would like to know if it's possible to create a left join twice on the same table with different where statements within them that create a new column so that the data returns 1 row per ID. Example data below:
ID | Title |
123| 1 |
123| 2 |
321| 1 |
321| 2 |
I've tried running this code but it gives me an error
Forgive me, I am new at SQL and am not sure I am even going about this right, but here is what I tried to do:
select c.ID, Title1, Title2
From c
left join (select b.title "title1"
from titles b
where title='1' and c.ID=b.ID)
left join (select b.title "title2"
from titles b
where title='2' and c.ID=b.ID)
Desired output
ID | Title1| Title2 |
123| 1 | 2 |
321| 1 | 2 |
You can use
select ID, min(title) as title1, max(title) as title2
from titles
group by ID
You can use 2 alias for the same table
select a.ID, a.Title Title1, b.Title Title 2
from titles a
inner join title b on a.id = b.id and a.Title = 1 and b.title = 2
Not sure how to do it with a LEFT JOIN but you can do it pretty easily with an INNER JOIN.
SELECT a.ID, a.Title, b.Title
FROM (
SELECT ID, Title
FROM a
WHERE Title=1
) a
INNER JOIN (
SELECT ID, Title
FROM b
WHERE Title=2
) b
ON a.ID = b.ID
You need a way to join your subqueries together which requires you to keep the ID field in each of the subqueries so it can be used in the JOIN condition.
If you really want to do this using left join:
select a.ID, Title1, Title2
From a left join
titles t1
on a.id = t1.id and t1.title = '1' left join
titles t2
on a.id = t2.id and t2.title = '2' ;
It is unclear what you are using for join keys between the tables.
I have the following between these two tables, id column and case column
Left Table Right Table
| id1 | case#1 | | case#1 | id1 |
| id2 | case#1 | | case#1 | id3 |
| id3 | case#2 | | case#2 | id1 |
As you can see case#1 is not assigned to id2 on the right table, therefore I would like to pull the (id2, case#1) record from the left table.
You would need to perform an OUTER JOIN with a multiple JOIN condition:
left_table as l right outer join right_table as r
on l.id = r.id and l.case_ = r.case_
where l.id IS NULL;
This will return non-matching rows from the left table
Have you tried a left join?
LEFT OUTER JOIN table ON table1.field1 = table2.field2
Depends on what you want. If you do INNER JOIN, you get the rows that match in Table1 AND Table2. If you do OUTER JOIN, you get all of Table1 and only the matching rows from Table2.
I've used LEFT JOIN and selected the record with NULL id in the Right Table using WHERE clause. See my query and demo below:
SELECT
*
FROM LeftTable A
LEFT JOIN RightTable B ON A.id=B.id
WHERE B.id IS NULL
DEMO HERE
I would use NOT EXISTS operation in that case.
SELECT l.id, l.value
FROM LeftTable l
WHERE NOT EXISTS (SELECT 1 FROM RightTable r WHERE r.id = l.id and r.case_value = l.case_value)
Efficiency comparing and the difference between NOT EXISTS vs. NOT IN vs. LEFT JOIN WHERE IS NULL are here
I have a two tables in my postgresql database.
Both tables have same columns.
How can i prefer values from tableA which are not null?
TableA
id | name
1 | val_a_1
2 | val_a_2
3 | (null)
TableB
id | name
1 | (null)
2 | val_b_2
3 | val_b_3
Result which i want to get:
id | name
1 | val_a_1
2 | val_a_2
3 | val_b_3
For now I've got it like this, but its more complicated, because there are lots of columns.
SELECT *
CASE
WHEN TableA.name is NULL or TableA.name = ''
THEN (SELECT TableB.name FROM TableB where TableB.id = 1)
ELSE TableA.name
END
AS name,
CASE
.
. another columns
.
END
Thanks
why not use COALESCE? Assuming all recordID in tableA is present on Table2
SELECT a.ID,
COALESCE(a.name, b.name) AS "Name"
FROM TableA a
INNER JOIN TableB b
ON a.ID = b.ID
SQLFIddle Demo
Conditional Expressions
The COALESCE function returns the first of its arguments (there can be more arguments) that is not null.
It's all about the COALESCE, not the join itself.
you can use a full outer join for the values which exist in tableA but not in tableB and vice versa:
select coalesce(tableA.ID, tableB.ID) as ID,
coalesce(tableA.Name, tableB.Name) as Name
from tableA full outer join tableB on tableA.ID = tableB.ID
I have a problem in writing sql query. Here is the illustration about my problem.
I have 2 tables in the database as follows :
| Table A | | Table B |
| idTableA | | idTableB |
| idPriority | | idReference |
Those tables above are related. The idReference in Table B is referring to idPriority in Table A. BUT if the value of the idPriority is NULL, then the idReference should be referring to idTableA. Hope you guys get the illustration and can help me working with this problem. Thx in advance.
Double-join method, easy to read
select
B.idTableB,
isnull(A1.idPriority, A2.idTableA) as RefValue
from
TableB as B
left join TableA as A1 on A1.idPriority = B.idReference
left join TableA as A2 on A1.idTableA = B.idReference
Single-join method, two IsNulls()'s:
select
B.idTableB,
isnull(A1.idPriority, A1.idTableA) as RefValue
from
TableB as B
left join TableA as A1 on isnull(A1.idPriority, A1.idTableA) = B.idReference
would the following construct work for you?
select *
from tableA join tableB on (join condition)
where (idpriority is not null)
union
select *
from tableA join tableB on (join condition)
where (idpriority is null)
select *
from tableB b
join tableA a
on
a.idPriority = b.idReference
or
(a.idPriority IS NULL AND b.idReference = a.idTableA)
I want to retrieve all records from one table when there are no matches in the second table.
So it is kind of the opposite of an inner join.
You need a LEFT JOIN WHERE IS NULL query (aka outer join):
SELECT table1.*
FROM table1
LEFT OUTER JOIN table2
ON table1.id = table2.id
WHERE table2.id IS NULL
Or a NOT IN:
SELECT *
FROM table1
WHERE id NOT IN (SELECT id FROM table2)
You have three options:
Correlated sub-query.
SELECT * FROM TableA
WHERE NOT EXISTS
(SELECT * FROM TableB WHERE TableB.ID = TableA.ID)
Non-correlated sub-query.
SELECT * FROM TableA
WHERE ID NOT IN (SELECT ID FROM TableB)
OUTER JOIN with NULL elimination.
SELECT * FROM TableA
LEFT [OUTER] JOIN TableB
ON TableA.ID = TableB.ID
WHERE TableB.ItsPrimaryKey IS NOT NULL
In the last example some DBMSes require the word OUTER, some permit it, and some do not allow it at all.
Depending on the DBMS, the various options might produce different execution plans and different performance. Select the one with good performance and that best expresses your intent.
It's an outer join:
SELECT *
FROM tableA AS a
LEFT JOIN tableB AS b USING(x)
Say you have:
tableA:
a | x
-----
1 | 1
3 | 3
table B:
b | x
-------
1 | 'a'
2 | 'b'
then the query above will give you
a | b | x
------------
1 | 'a' | 1
3 | NULL | 3
if you want
a | b | x
----------------
1 | 'a' | 1
NULL | 'b' | 2
3 | NULL | 3
you have to use FULL OUTER JOIN instead of LEFT JOIN.
EDIT: As Larry Lustig told me (and I think is correct after rereading the question) the OP does not want any rows from B. So the query should be:
SELECT a.*
FROM tableA AS a
LEFT JOIN tableB AS b USING(x)
WHERE b.x IS NULL
that will yield
a | x
-------
3 | 3
The "opposite" of inner join is called outer join.
Outer join. Technically possibly FULL OUTER JOIN ;)
Adding to the Solution of Johannes Weiß the solution to your other question about finding objects in table a without objects in table b:
SELECT *
FROM tableA AS a
LEFT JOIN tableB AS b
USING(x)
WHERE b.foo IS NULL
You are looking for LEFT JOIN or FULL OUTER JOIN
Not all DBMS support FULL though.
Simulation of it is possible with UNION, example in MySQL:
SELECT * FROM t1
LEFT JOIN t2 ON t1.id = t2.id
UNION
SELECT * FROM t1
RIGHT JOIN t2 ON t1.id = t2.id
I believe you are looking for FULL OUTER JOIN (works with Oracle 9i+).
EDIT: didn't read your question well... LEFT JOIN if you only want NULL values for the second table