I am using MS SQL SERVER 2008R2. i have two tables A and B as
create table A(
id int primary key, name Varchar(20));
create table B(
id int primary key, user_name Varchar(20));
insert into A values(1,'A1');
insert into A values(2,'A2');
insert into A values(3,'A3');
insert into A values(4,'A4');
insert into A values(5,'A5');
Now my problem is :
select A.*
from A left outer join B on A.id = B.id
where B.user_name like '%';
or
select A.*
from A left outer join B on A.id = B.id
where B.user_name like '%%';
Above written query does not return any records even though left table have 5 entries in it. without any filter on right table it works fine.
select A.* from A left outer join B on A.id = B.id
this query will give you out put like this...
id name id user_name
1 A1 NULL NULL
2 A2 NULL NULL
3 A3 NULL NULL
4 A4 NULL NULL
5 A5 NULL NULL
and you are comparing username using like with null
select A.* from A left outer join B on A.id = B.id where B.user_name like '%%';
hence it will not give you any output
you should try following query
select A.*,b.* from A left outer join B on A.id = B.id where (b.user_name like '%%' or b.user_name is null)
In your scenario...first left join is happening it is finding 5 entries and then on that record set sql sever is applying filter of user_name and as user_name for all rows is null..no records are getting displayed.
you can change your query to
select A.* from A left outer join B on A.id = B.id where ISNULL(B.user_name,'') like '%%';
You are using wild card for comparing null values as well,
Use this,
SELECT a.* FROM a LEFT OUTER JOIN b ON a.id = b.id WHERE b.user_name LIKE '%' OR b.user_name IS NULL;
Since all values in table B are NULL, any wildcard match on NULL values will return NULL.
So the condition where B.user_name like '%'; translates into where NULL like '%'; which evaluates to NULL as NULL cannot be compared with any value.
select A.* from A left outer join B on
A.id = B.id where COALESCE(B.user_name,'') like '%%';
select A.* from A left outer join B on
A.id = B.id where COALESCE(B.user_name,'') like '%';
supporting sql fiddle : http://sqlfiddle.com/#!6/1ca91/8
Note that the COALESCE is ANSI, and therefore supported in Oracle, SQL Server and PostGres and does shortcut evaluation. n
Edit: Based on new information that this same query should work in all SQL Server, PostGres and Oracle. I am changing the SQL query to
use COALESCE instead which is supported in all
Unless you use ISNULL() and check like this where
ISNULL(B.user_name,'') like '%';
select A.* from A left outer join B on
A.id = B.id where ISNULL(B.user_name,'') like '%%';
select A.* from A left outer join B on
A.id = B.id where ISNULL(B.user_name,'') like '%';
See this fiddle
http://sqlfiddle.com/#!6/1ca91/6
Please try this one:
select A.* from A
left outer join (SELECT * FROM B where user_name like '%') X on A.id = X.id;
Related
I have the following Hive query:
select *
from A
left outer join B
on A.ID = B.ID
where B.ID IS NULL
The result produces duplicate data but I need only non-duplicate records.
After some research, I tried the below query:
select *
from (
select *
from A
left outer join on B
where A.ID = B.ID AND B.ID IS NULL ) join_result
group by jojn_result.ID
It's showing an ambiguous column reference ID error.
I do not have the columns name of table A.
Please help me to identify the solution to this .
Thank you .
Hmmm . . . How about select:
Select A.*
from A left outer join
B
on A.ID = B.ID
where B.ID IS NULL;
I removed the B columns because they are not needed.
One of your join columns may have NULL values. Whenever there is NULL in any of the join key values, it will skip that column. Try replacing the NULL with some default value while joining using NVL or COALESCE. I was looking for same answer and saw your post here. But there was no solution. But since i found the solution I just wanted to post here so that someone can benefit.
select *
from A
left outer join B
on coalesce(A.ID,000) = coalesce(B.ID,000)
where B.ID IS NULL
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'm trying to do a simple LEFT JOIN with tables with 2 IDs - basically an ID and Sub-ID. Each row has an ID, but not necessarily a Sub-ID. When a Sub-ID exists, I want to join based on that, if not join on the ID. I'd imagine something like
SELECT ...
FROM tablename a
LEFT JOIN tablename b
ON CASE WHEN SUB_ID IS NOT NULL THEN
a.SUB_ID = b.SUB_ID
ELSE
a.ID = b.ID END
AND
a.otherfield = b.otherfield
But I couldn't get anything like this to work, so instead I had to do 2 queries with a UNION (one that joined on SUB_ID WHERE SUB_ID IS NOT NULL and another that joined on ID WHERE SUB_ID IS NULL.) It worked but I can't imagine there isn't a way to do it. If it helps, my ID and SUB_ID values look like this:
ID SUB_ID
10000 NULL
10001 NULL
10001 10001-3
10001 10001-5
10014 NULL
Any suggestions on how to achieve this without doing a UNION? Thanks in advance!!
We can use COALESCE for this purpose:
SELECT ...
FROM tablename a
LEFT JOIN tablename b
ON COALESCE(a.SUB_ID,a.ID) = COALESCE(b.SUB_ID,b.ID)
COALESCE returns value of first not null parameter from left.
Here is the code at SQL Fiddle
This should work for you.
SELECT ...
FROM tablename a
LEFT JOIN tablename b
ON ((b.SUB_ID IS NOT NULL AND a.SUB_ID = b.SUB_ID) OR
(a.ID = b.ID))
AND a.otherfield = b.otherfield
Interesting.
SELECT ...
FROM tablename a
LEFT JOIN tablename b
ON (
a.SUB_ID = b.SUB_ID
OR (a.SUB_ID IS NULL AND b.SUB_ID IS NULL AND a.ID = b.ID)
)
AND a.otherfield = b.otherfield
That might well work. It's NOT going to be fast, though.
Depending on the state of your data and what you want to achieve, you might want to change the join clause to
ON (
a.SUB_ID = b.SUB_ID
OR (a.SUB_ID IS NULL AND a.ID = b.ID)
OR (b.SUB_ID IS NULL AND a.ID = b.ID)
)
AND a.otherfield = b.otherfield
... instead.
You could JOIN the table twice:
SELECT ...
FROM tablename a
LEFT JOIN tablename b
ON a.SUB_ID = b.SUB_ID
AND a.otherfield = b.otherfield
LEFT JOIN tablename c
ON a.ID = b.ID
AND a.SUB_ID IS NULL
AND a.otherfield = c.otherfield
Then use ISNULL to get the columns, e.g.
ColumnName = ISNULL(b.ColumnName, c.ColumnName)
It depends on your indexes, but I suspect this may get optimised better than having a conditional join clause.
Try something like this:
SELECT *
FROM TABLENAME A
LEFT JOIN TABLENAME B
ON (A.SUB_ID IS NOT NULL AND A.SUB_ID = B.SUB_ID)
OR (A.SUB_ID IS NULL AND A.ID = B.ID)
If i write a sql:
select *
from a,b
where a.id=b.id(+)
and b.val="test"
and i want all records from a where corresponding record in b does not exist or it exists with val="test", is this the correct query?
You're much better off using the ANSI syntax
SELECT *
FROM a
LEFT OUTER JOIN b ON( a.id = b.id and
b.val = 'test' )
You can do the same thing using Oracle's syntax as well but it gets a bit hinkey
SELECT *
FROM a,
b
WHERE a.id = b.id(+)
AND b.val(+) = 'test'
Note that in both cases, I'm ignoring the c table since you don't specify a join condition. And I'm assuming that you don't really want to join A to B and then generate a Cartesian product with C.
Move the condition into the JOIN clause and use the ANSI standard join pattern.
SELECT NameYourFields,...
FROM A
LEFT OUTER JOIN B
ON A.ID = B.ID
AND B.VAL = 'test'
INNER JOIN C
ON ...
A LEFT OUTER JOIN is one of the JOIN operations that allow you to specify a join clause. It preserves the unmatched rows from the first (left) table, joining them with a NULL row in the shape of the second (right) table.
So you can do as follows :
SELECT
FROM a LEFT OUTER JOIN b
ON a.id = b.id
--Note that you have used double quote "test" which is not used for varchar in SQL you should use single quote 'test'
AND b.val = 'test';
SELECT * FROM abc a, xyz b
WHERE a.id = b.id
AND b.val = 'test'
I need to simulate the left join effect without using the "left join" key.
I have two tables, A and B, both with id and name columns. I would like to select all the dbids on both tables, where the name in A equals the name in B.
I use this to make a synchronization, so at the beginning B is empty (so I will have couples with id from A with a value and id from B is null). Later I will have a mix of couples with value - value and value - null.
Normally it would be:
SELECT A.id, B.id
FROM A left join B
ON A.name = B.name
The problem is that I can't use the left join and wanted to know if/how it is possible to do the same thing.
you can use this approach, but you must be sure that the inner select only returns one row.
SELECT A.id,
(select B.id from B where A.name = B.name) as B_ID
FROM A
Just reverse the tables and use a right join instead.
SELECT A.id,
B.id
FROM B
RIGHT JOIN A
ON A.name = B.name
I'm not familiar with java/jpa. Using pure SQL, here's one approach:
SELECT A.id AS A_id, B.id AS B_id
FROM A INNER JOIN B
ON A.name = B.name
UNION
SELECT id AS A_id, NULL AS B_id
FROM A
WHERE name NOT IN ( SELECT name FROM B );
In SQL Server, for example, You can use the *= operator to make a left join:
select A.id, B.id
from A, B
where A.name *= B.name
Other databases might have a slightly different syntax, if such an operator exists at all.
This is the old syntax, used before the join keyword was introduced. You should of course use the join keyword instead if possible. The old syntax might not even work in newer versions of the database.
I can only think of two ways that haven't been given so far. My last three ideas have already been given (boohoo) but I put them here for posterity. I DID think of them without cheating. :-p
Calculate whether B has a match, then provide an extra UNIONed row for the B set to supply the NULL when there is no match.
SELECT A.Id, A.Something, B.Id, B.Whatever, B.SomethingElse
FROM
(
SELECT
A.*,
CASE
WHEN EXISTS (SELECT * FROM B WHERE A.Id = B.Id) THEN 1
ELSE 0
END Which
FROM A
) A
INNER JOIN (
SELECT 1 Which, B.* FROM B
UNION ALL SELECT 0, B* FROM B WHERE 1 = 0
) B ON A.Which = B.Which
AND (
A.Which = 0
OR (
A.Which = 1
AND A.Id = b.Id
)
)
A slightly different take on that same query:
SELECT A.Id, B.Id
FROM
(
SELECT
A.*,
CASE
WHEN EXISTS (SELECT * FROM B WHERE A.Id = B.Id) THEN A.Id
ELSE -1 // a value that does not exist in B
END PseudoId
FROM A
) A
INNER JOIN (
SELECT B.Id PseudoId, B.Id FROM B
UNION ALL SELECT -1, NULL
) B ON A.Which = B.Which
AND A.PseudoId = B.PseudoId
Only for SQL Server specifically. I know, it's really a left join, but it doesn't SAY LEFT in there!
SELECT A.Id, B.Id
FROM
A
OUTER APPLY (
SELECT *
FROM B
WHERE A.Id = B.Id
) B
Get the inner join then UNION the outer join:
SELECT A.Id, B.Id
FROM
A
INNER JOIN B ON A.name = B.name
UNION ALL
SELECT A.Id, NULL
FROM A
WHERE NOT EXISTS (
SELECT *
FROM B
WHERE A.Id = B.Id
)
Use RIGHT JOIN. That's not a LEFT JOIN!
SELECT A.Id, B.Id
FROM
B
RIGHT JOIN A ON B.name = A.name
Just select the B value in a subquery expression (let's hope there's only one B per A). Multiple columns from B can be their own expressions (YUCKO!):
SELECT A.Id, (SELECT TOP 1 B.Id FROM B WHERE A.Id = B.Id) Bid
FROM A
Anyone using Oracle may need some FROM DUAL clauses in any SELECTs that have no FROM.
You could use subqueries, something like:
select a.id
, nvl((select b.id from b where b.name = a.name), "") as bId
from a
you can use oracle + operator for left join :-
SELECT A.id, B.id
FROM A , B
ON A.name = B.name (+)
Find link :-
Oracle "(+)" Operator
SELECT A.id, B.id
FROM A full outer join B
ON A.name = B.name
where A.name is not null
I'm not sure if you just can't use a LEFT JOIN or if you're restricted from using any JOINS at all. But as far as I understand your requirements, an INNER JOIN should work:
SELECT A.id, B.id
FROM A
INNER JOIN B ON A.name = B.name
Simulating left join using pure simple sql:
SELECT A.name
FROM A
where (select count(B.name) from B where A.id = B.id)<1;
In left join there are no lines in B referring A so 0 names in B will refer to the lines in A that dont have a match
+ or A.id = B.id in where clause to simulate the inner join