Currently I have joined two tables using inner join , like following
SELECT A.*,B.*
FROM A,B
WHERE A.COLUMN_A = B.COLUMN_B
now I want to join Left outer join to above results , lets say I want to join Table C
So I did like following
SELECT A.*,B.*
FROM A,B
LEFT OUTER JOIN C ON B.COLUMN_X = C.COLUMN_X
WHERE A.COLUMN_A = B.COLUMN_B
this is executing without errors in SQL navigator, But in this result I cannot see any output.
anything wrong in this query , please advise
Change it to have proper join syntax like
SELECT A.*,B.*
FROM A
INNER JOIN B ON A.COLUMN_A = B.COLUMN_B
LEFT OUTER JOIN C ON B.COLUMN_X = C.COLUMN_X;
Better change all to outer join
SELECT A.*,B.*
FROM A
LEFT JOIN B ON A.COLUMN_A = B.COLUMN_B
LEFT OUTER JOIN C ON B.COLUMN_X = C.COLUMN_X;
Use this
SELECT A.*,B.*,C.*
FROM A
INNER JOIN B
ON A.COLUMN_A = B.COLUMN_B
LEFT OUTER JOIN C
ON B.COLUMN_X = C.COLUMN_X
If you absolutely have to use legacy syntax, then use this. But I won't recommend it.
SELECT A.*,B.*,C.*
FROM A,B,C
where A.COLUMN_A = B.COLUMN_B
AND
B.COLUMN_X = C.COLUMN_X (+)
Related
I have some very old Oracle SQL code I need to review, as per below and am trying to understand what the (+) operator is doing in the where clause after the first use of it
select *
from table_a a,
table b b
where
a.id = b.id (+)
and b.seq_nb (+) = 1
and b.type_cd (+) = 'DOLLR'
I thought (+) was a outer join equivalent, so
from table_a a,
table b b
where
a.id = b.id (+)
would be the same as
from table a a left outer join table b b on a.id=b.id
so how can you have outer joins to hard coded variables as below?
b.seq_nb (+) = 1
and b.type_cd (+) = 'DOLLR'
Any help would be greatly appreciated, thank you!
It's the same as:
select *
from table_a a
left outer join table_b b
on a.id = b.id
and b.type_cd = 'DOLLR'
and b.seq_nb = 1
Sometimes also referred to as a "filtered outer join".
It is equivalent to an outer join with a derived table:
select *
from table_a a
left outer join (
select *
from table_b
where b.type_cd = 'DOLLR'
and b.seq_nb = 1
) b on a.id = b.id
I have a question about Oracle's (+) left/right join in a scenario where the 2 tables were joined on 2 columns but one column was with (+) but the other was without the (+). I am trying to convert a whole bunch of queries and changing them to the proper join and curious about this one.
The query using the (+) join works but when convert to a proper left/right join the results are different. See sample code.
--OLD
select *
from tbl1 a, tbl2 b
where a.col1 = b.col1 (+)
and a.col2 = b.col2
--CONVERTED
select *
from tbl1 a
left join tbl2 b on a.col1 = b.col1 and a.col2 = b.col2
Is there a way to make the CONVERTED code work just like the OLD?
Thanks.
RS..
Your first query will not do left outer join but it will do inner join as there are condition without (+) that is why using new format of join is more suitable for readability and less complexity.
If you really want to stick to old join format that is using (+) then you can use the following code.
select *
from tbl1 a, tbl2 b
where a.col1 = b.col1 (+)
and a.col2 = b.col2 (+)
Above code will do proper left outer join as all the condition pertaining to the table are now tagged with (+)
BUT, It is recommended that you use new join format, that is, use LEFT JOIN syntax.
Hope, It will clear your doubts.
Cheers!!
If you simply want to convert to ANSI syntax, then you should know that your old query is executed as an inner join and not as an outer join. The converted query should be:
select *
from tbl1 a
join tbl2 b on (
b.col1 = a.col1
and b.col2 = a.col2
)
If you think you have stumbled on a bug, and that the query should be executed as an outer join, then your query will be:
select *
from tbl1 a
left join tbl2 b on (
b.col1 = a.col1
and b.col2 = a.col2
)
If you want to repeat the same mistake as the original query, i.e appearing to be an outer join while actually being executed as an inner join... the query will be:
select *
from tbl1 a
left join tbl2 b on (
b.col1 = a.col1
)
where b.col2 = a.col2
I am trying to optimize my LINQ query performance, and I've noticed a lot of LEFT OUTER JOINs being generated. I know that in SQL, there are some cases in which a single row subquery works better than the equivalent LEFT OUTER JOIN.
For example:
Query 1:
select f.FacilityName, p.Id PatientId, u.DOB, (select u2.NameComputed from adm.Staffs s inner join dbo.AspNetUsers u2 on s.UserId = u2.Id where s.Id = p.StaffId) AssignedTo
from ptn.Patients p
inner join dbo.AspNetUsers u on p.UserId = u.Id
inner join hco.Hcos f on p.HcoId = f.Id
where p.IsRemoved = 0
Query 2:
select f.FacilityName, p.Id PatientId, u.DOB, u2.NameComputed
from ptn.Patients p
inner join dbo.AspNetUsers u on p.UserId = u.Id
inner join hco.Hcos f on p.HcoId = f.Id
left outer join adm.Staffs s on p.StaffId = s.Id
left outer join dbo.AspNetUsers u2 on s.UserId = u2.Id
where p.IsRemoved = 0
Query 1 takes less than a second. Query 2 takes about 45 seconds. If I wanted to make sure LINQ is structured in such a way as to take advantage of this in some cases, how would I go about doing that? That is, is there a way to write a LINQ statement that produces a subquery instead of a LEFT OUTER JOIN?
What is the best way to structure/write a query in Hive when I have a complex sub-query that is repeated multiple times throughout the select statement?
I originally created a temporary table for the sub-query which was refreshed before each run. Then I began to use a CTE as part of the original query (discarding the temp table) for readability and noticed degraded performance. This made me curious about which implementation methods are best with respect to performance when needing to reuse sub-queries.
The data I am working with contains upwards of 10 million records. Below is an example of the query I wrote that made use of a CTE.
with temp as (
select
a.id,
x.type,
y.response
from sandbox.tbl_form a
left outer join sandbox.tbl_formStatus b
on a.id = b.id
left outer join sandbox.tbl_formResponse y
on b.id = y.id
left outer join sandbox.tbl_formType x
on y.id = x.typeId
where b.status = 'Completed'
)
select
a.id,
q.response as user,
r.response as system,
s.response as agent,
t.response as owner
from sandbox.tbl_form a
left outer join (
select * from temp x
where x.type= 'User'
) q
on a.id = q.id
left outer join (
select * from temp x
where x.type= 'System'
) r
on a.id = r.id
left outer join (
select * from temp x
where x.type= 'Agent'
) s
on a.id = s.id
left outer join (
select * from temp x
where x.type= 'Owner'
) t
on a.id = t.id;
There are issues in your query.
1) In the CTE you have three left joins without ON clause. This may cause serious performance problems because joins without ON clause are CROSS JOINS.
2) BTW where b.status = 'Completed' clause converts LEFT join with table b to the inner join though still without ON clause it multiplicates all records from a by all records from b with a where.
3) Most probably you do not need CTE at all. Just join correctly with ON clause and use case when type='User' then response end + aggregate using min() or max() by id:
select a.id
max(case when x.type='User' then y.response end) as user,
max(case when x.type='System' then y.response end) as system,
...
from sandbox.tbl_form a
left outer join sandbox.tbl_formStatus b
on a.id = b.id
left outer join sandbox.tbl_formResponse y
on b.id = y.id
left outer join sandbox.tbl_formType x
on y.id = x.typeId
where b.status = 'Completed' --if you want LEFT JOIN add --or b.status is null
group by a.id
I need to use left outer join on three table. Example I have three table called A,B and C. I want result like
A left outer join ( B left outer join c).
What is the best way to do it.
I have written something like this.
select * from A,B,C where A.column_a=B.column_a(+) and B.column_b=C.column_b(+);
depending on how the tables are related (which is not entirely clear from your question),
select *
from A
left join B on b.column_a = a.column_a
left join C on c.column_b = b.column_b
or,
select *
from A
left join (B left join C on c.column_b = b.column_b)
on b.column_a = a.column_a