I have a long stored procedure and I would like to make a slight modification to the procedure without having to create a new one(for maintenance purposes).
Is it possible to use a IF or CASE in the FROM statement of the select statement to join other tables?
Like this:
from tableA a
join tableB b a.indexed = c.indexed
IF #Param='Y'
BEGIN
join tableC c a.indexed = c.indexed
END
It didn't seem to work for me. But I am wondering if this is even possible and/or if this even makes sense to do.
Thanks.
No, it is not possible. You can only accomplish this through the use of dynamic SQL.
The Curse and Blessings of Dynamic SQL
An Intro to Dynamic SQL
I would not advise using Dynamic SQL, there are most likely better ways to perform this operation but you would have to provide more info.
You can achieve something like it if you have a left outer join
Consider
declare #param bit = 1
select a.*, b.*, c.* from a
inner join b on a.id = b.a_id
left outer join c on b.id = c.b_id and #param = 1
This will return all columns from a, b, c.
Now try with
declare #param bit = 0
This will return all columns from a and b, and nulls for columns of c.
It won't work if both joins are inner.
No this is not possible. Your best bet would probably be to select from both tables and only include the data your care about. If you provide an example of what you are trying to do I can provide a better answer.
Attempt at an example:
SELECT t1.id, COALESCE(t2.name, t3.name)
FROM Table1 as t1
LEFT JOIN Table2 as t2
ON t1.id = t2.id
LEFT JOIN Table2 as t3
ON t1.id = t3.id
While what you proposed is not possible, you can play with your where conditions:
from tableA a
inner join tableB b ON a.indexed = c.indexed
left join tableC c ON a.indexed = c.indexed AND 1 = CASE #Param WHEN 'Y' THEN 1 ELSE 0 END
More performant would be to just doing a big
IF #Param='Y' THEN
from tableA a
inner join tableB b ON a.indexed = c.indexed
ELSE
from tableA a
inner join tableB b ON a.indexed = c.indexed
left join tableC c ON a.indexed = c.indexed
You haven't revealed you SELECT clause. The essence of what you want is as follows:
SELECT indexed
FROM tableA
INTERSECT
SELECT indexed
FROM tableB
INTERSECT
SELECT indexed
FROM tableC
WHERE #Param = 'Y'
Then use this table expression as dictated by your SELECT clause e.g. say you only want to project tableA:
WITH T
AS
(
SELECT indexed
FROM tableA
INTERSECT
SELECT indexed
FROM tableB
INTERSECT
SELECT indexed
FROM tableC
WHERE #Param = 'Y'
)
SELECT *
FROM tableA
WHERE indexed IN ( SELECT indexed FROM T );
Related
I'd like to implement an antijoin on two table but using two keys so that the result is all rows in Table A that do not contain the combinations of [key_1, key_2] found in Table B. How can I write this query in SQL?
If you want an anti-left join, the logic is:
select a.*
from tablea a
left join tableb b on b.key_1 = a.key_1 and b.key_2 = a.key_2
where b.key_1 is null
As for me, I like to implement such logic with not exists, because I find that it is more expressive about the intent:
select a.*
from tablea a
where not exists (
select 1 from tableb b where b.key_1 = a.key_1 and b.key_2 = a.key_2
)
The not exists query would take advantage of an index on tableb(key_1, key_2).
select a.*
from table_a a
left anti join table_b b on a.key_1 = b.key_1 and a.key_2 = b.key_2;
Does SQL allow some form of conditional "table choosing" within the Join statement? ie. selecting a different table to join based on a predefined variable/condition.
define var = 1
select *
from tbl
join (case when &var=1 then tblA when &var=2 then tblB else tblC end) a on tbl.id = a.id
The error I get when attempting this method is ORA-00905: missing keyword.
No. Neither SQL nor Oracle allow this, unless you use dynamic SQL.
Assuming the tables have the same columns, you could write this logic as:
select *
from tbl join
(select a.* from tblA where &var = 1 union all
select b.* from tblB where &var = 2 union all
select c.* from tblC where &var not in (1, 2)
) abc
on tbl.id = abc.id;
You still need to specify all joins ahead of time and they would have to be left outer joins, but you can rewrite your statement like this. This way will work regardless of the number of fields in each of the tables (requirement for the union), and if they are named differently then you can access the appropriate field by name.
DECLARE #var int
SET #var=1
select tbl.*, tblA.ShippingName, tblB.BillingName, tblC.OtherName
from tbl
left outer join tblA on tbl.id = tblA.id and #var = 1
left outer join tblB on tbl.id = tblB.id and #var = 2
left outer join tblC on tbl.id = tblC.id and #var = 3
Here is pseudocode of what I am trying to achieve
Select * from TableA
if(TableA.criteria != 1)
inner join TableB.criteria = TableA.criteria
I must do it in view can use sp, functions, etc.
Thanks for any help you will be able to provide
Is this what you want?
Select a.*, b.* from TableA a join TableB b
on b.criteria = case when a.Criteria = 1
then 1 else null end
This may be what you want:
select a.*, b.*
from a left join
b
on b.criteria = a.criteria and b.criteria = 1;
The left join will keep all rows in a, even when the on condition is not true. The extra columns from b will be NULL, unless the criterias are both "1".
I am trying to join 4 tables. Currently I've achieved it by doing this.
SELECT columns
FROM tableA
LEFT OUTER JOIN tableB ON tableB.address_id = tableA.address_id
INNER JOIN tableC ON tableC.company_id = tableA.company_id AND tableC.client_id = ?
UNION
SELECT columns
FROM tableA
LEFT OUTER JOIN tableB ON tableB.address_id = tableA.gaddress_id
INNER JOIN tableD ON tableD.company_id = tableA.company_id AND tableD.branch_id = ?
The structure of tableC and tableD is very similar. Let's say that tableC contains data for clients. And tableD contains data for client's branch. tableA are companies and tableB are addresses My goal is to get data from tableA that are joined to table B (All companies that has addresses) and all the data from tableD and also from tableC.
This wroks nice, but I am afraid that is would be very slow.
I think you can trick it like this:
First UNION between C,D and only the join to the rest of the query, it should improve the query significantly :
SELECT columns
FROM TableA
LEFT OUTER JOIN tableB ON tableB.address_id = tableA.address_id
INNER JOIN(SELECT Columns,'1' as ind_where FROM tableC
UNION ALL
SELECT Columns,'2' FROM TableD) joined_Table
ON (joined_Table.company_id = tableA.company_id AND joined_Table.New_Col_ID= ?)
The New_Col_ID -> just select both branch_id and client_id in the same column and alias it as New_Col_ID or what ever
In addition you can index the tables(if not exists yet) :
TableA(address_id,company_id)
TableB(address_id)
TableC(company_id,client_id)
TableD(company_id,branch_id)
Why should that be slow? You select client adresses and branch addresses and show the complete result. That seems straight-forward.
You join on IDs and this should be fast (as there should be indexes available accordingly). You may want to introduce composite indexes on
create index idx_c on tableC(client_id, company_id)
and
create index idx_d on tableD(branch_id, company_id)
However: UNION is a lot of work for the DBMS, because it has to look for and eliminate duplicates. Can there even be any? Otherwise use UNION ALL.
Try CTE so that you don't have to go through TableA and TableB twice for the union.
; WITH TempTable (Column1, Column2, ...)
AS ( SELECT columns
FROM tableA
LEFT OUTER JOIN tableB
ON tableB.address_id = tableA.gaddress_id
)
SELECT Columns
FROM TempTable
INNER JOIN tableC
ON tableC.company_id = tableA.company_id AND tableC.client_id = ?
UNION
SELECT Columns
FROM TempTable
INNER JOIN tableD ON tableD.company_id = tableA.company_id AND tableD.branch_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'