In SQL I am trying to combine create a column id_main2 (after a right join) that is equal the value of column id_main (coming from a) if not NULL and the value of id (coming from b) if id_main is NULL.
Below is the join code followed by the desired output. How can I create this id_main2 column?
SELECT * FROM a
RIGHT JOIN b on a.id = b.id;
id_main id boy id girl id_main2
10 1 Alex 1 Alice 10
11 2 Bruce 2 Brunet 11
NULL NULL NULL 5 Emma 5
NULL NULL NULL 6 Fabia 6
I think you just want coalesce():
select a.*, b.*,
coalesce(a.id_main, b.id)
from b left join
a
on a.id = b.id;
I strongly prefer left join to right join, so I rearranged the tables in the from clause.
You can either use coalesce()
select
coalesce(a.id_main, b.id) as id_main2
from a
right join b on a.id = b.id;
or case when
select
case when a.id is not null then a.id
else b.id end as id_main2
from a
right join b on a.id = b.id;
Related
I have two tables:
Table A:
id names
1 a
2 b
3 c
and Table B:
id names
1 x
2 y
I'd like to perform a left join of Table B on Table A that results in the following table:
id names
1 x
2 y
3 c
How can I do this in Microsoft SQL?
You could use COALESCE:
SELECT a.id, COALESCE(b.name, a.name) AS name
FROM tab1 a
LEFT JOIN tab2 b
ON a.id = b.id
I think you just want coalesce():
select a.id, coalesce(b.name, a.name) as name
from a left join
b
on a.id = b.id;
I'm trying to join two tables like this:
Table A
ID Value1
1 A
2 B
3 C
Table B
ID Value2
1 A
3 B
4 C
Result should be:
ID Value1 Value2
1 A A
2 B null
3 C B
4 null C
I.e. join Table A to Table B on ID. If ID doesn't exist in Table A, add the ID from Table B.
The closest I've come is:
SELECT
a.ID, a.Value1, b.Value2
FROM
TableA a
OUTER JOIN
TableB b ON a.ID = b.ID
That gives me the new rows from TableB, but the ID is null.
How can I accomplish this?
You are very close, you just need a little push in the right direction:
SELECT COALESCE(a.ID, B.ID) As ID, a.Value1, b.Value2
FROM TableA a
FULL OUTER JOIN TableB b ON a.ID=b.ID
The COALESCE function returns the first parameter it gets that is not null. since this is a full outer join, a.id will be null on one row and b.id would be null on a different row.
Try this:
SELECT *
FROM TableA A
FULL OUTER JOIN TableB B
ON A.ID = B.ID;
Just a note: you should not name your tables in SQL with spaces in them.
Remember the basic for joining different tables
SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name=table2.column_name;
For your case:
SELECT a.value1, b.value2
FROM TableA a
FULL OUTER JOIN TableB b ON a.ID=b.ID
remember full outer join
The FULL OUTER JOIN keyword returns all rows from the table (tableA) and from the table (tableB) and the FULL OUTER JOIN keyword combines the result of both LEFT and RIGHT joins.
I have a table name "a"
Id name
1 abc
2 xyz
3 mmm
4 xxx
and Other table name is "b"
Id suId
3 2
3 1
My requirement is get detail from "a" table from "b" table where id=3. Any help?
SELECT a.Id, a.name, b.Id, b.suId FROM b JOIN a ON b.suId = a.Id WHERE b.Id = 3;
I wont recommend join for this kind of scenarios(you want all details from Table A whose ids are in Table B suId column, where Table B id should be 3., Its bad English but hope you got me and may be i got you too.)
SELECT a.name FROM a
WHERE
a.id IN(SELECT b.suId FROM b WHERE b.id = 3);
If you want to use join only then,
SELECT a.name FROM a,b
WHERE a.id = b.suId
AND
b.id = 3;
Simple answer:
SELECT a.Id,a.name FROM a,b
WHERE a.Id=b.suId AND b.Id=3
It will give you the result:
Id Name
1 abc
2 xyz
See result in SQL Fiddle
This should get the job done:
SELECT * FROM table_a a JOIN table_b b ON b.suId = a.Id WHERE b.Id = 3;
You can try this...You can try different JOIN clauses like INNER JOIN, LEFT OUTER JOIN or just simply JOIN etc. You will get different number of rows depending on field connections from 1 table to the other.
SELECT T1.*
FROM a T1
INNER JOIN b T2
ON T1.Id = T2.Id
WHERE T1.Id='3'
This is probably a really easy question, it's just very hard to google a word like "All".
SELECT a.Id, Max(b.Number)
FROM Table1 a
JOIN Table2 b
ON a.FK = b.Id
GROUP BY a.Id
But I want to add a where clause that specifies that all b.Id's linked to an a.FK must have values. So basically I don't want to select the a.Id grouping of b.Id's where any of those b.Id's are null. Hope I made that clear, let me know if I need to elaborate. Thanks.
Edit - For some clarification (Changed the query above as well):
Table1
Id, FK
1 1
1 2
2 3
3 4
3 5
3 6
Table 2
Id Number
1 1
2 NULL
3 10
4 20
5 30
6 40
I would want my query to show:
a.Id Max Number
2 10
3 40
(Notice that a.Id = 1 doesn't show up because one of the b.Number fields is null)
select t1.Id, max(Number) as [Max Number]
from Table1 t1
left join Table2 t2 ON t1.FK=t2.Id and t2.Number is not null
group by t1.Id
having count(distinct t1.FK) = count(distinct t2.Id)
Okay, you are asking a totally different question from the one I thought you were. I'm replacing my answer.
The way I would handle this is to join a to b twice -- once to get all matching rows in b, and a second join to search for rows in b where Number is null. If no such row exists, then we know they're all non-null.
SELECT a.Id, Max(b1.Number)
FROM Table1 a
JOIN Table2 b1 ON a.FK = b1.Id
LEFT OUTER JOIN Table2 b2 ON a.FK = b2.Id AND b2.Number IS NULL
WHERE b2.Id IS NULL
GROUP BY a.Id
b2.Id will be null only if no row is found where b2.Number is null.
SELECT a.Id, Max(b.Id)
FROM Table1 a
JOIN Table2 b
ON a.FK = b.Id
WHERE b.Id is NOT NULL
GROUP BY a.Id
Suppose we have a table A:
itemid mark
1 5
2 3
and table B:
itemid mark
1 3
3 5
I want to join A*B on A.itemid=B.itemid both right and left ways. i.e. result:
itemid A.mark B.mark
1 5 3
2 3 NULL
3 NULL 5
Is there a way to do it in one query in MySQL?
It's called a full outer join and it's not supported natively in MySQL, judging from its docs. You can work around this limitation using UNION as described in the comments to the page I linked to.
[edit] Since others posted snippets, here you go. You can see explanation on the linked page.
SELECT *
FROM A LEFT JOIN B ON A.id = B.id
UNION ALL
SELECT *
FROM A RIGHT JOIN B ON A.id = B.id
WHERE A.id IS NULL
Could do with some work but here is some sql
select distinct T.itemid, A.mark as "A.mark", B.mark as "B.mark"
from (select * from A union select * from B) T
left join A on T.itemid = A.itemid
left join B on T.itemid = B.itemid;
This relies on the left join, which returns all the rows in the original table (in this case this is the subselect table T). If there are no matches in the joined table, then it will set the column to NULL.
This works for me on SQL Server:
select isnull(a.id, b.id), a.mark, b.mark
from a
full outer join b on b.id = a.id