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;
Related
I have this SQL problem: I have tables A and B. Table A has columns id and name, Table B amount and id which is a foreign key to table A.id.
I need to return all table A rows that don't have their id stored in table B. Any ideas?
So the complete opposite is:
SELECT *
FROM a
LEFT OUTER JOIN b ON a.id = b.id;
Here row what I need is left out of result
Just add a where clause:
SELECT a.*
FROM a LEFT OUTER JOIN
b
ON a.id = b.id
WHERE b.id IS NULL;
You can also use NOT EXISTS:
select a.*
from a
where not exists (select 1 from b where b.id = a.id);
In most databases, the two methods typically have similar performance.
I have two tables:
I am looking for the results like mentioned in the last.
I tried union (only similar col can be merged), left join, right join i am getting repeated fields in Null areas what can be other options where i can get null without column repeating
A full join would get all results from both tables.
select
A.ID,
A.ColA,
A.ColB,
B.ColC,
B.ColD
from TableA A
full join Table B on A.ID = B.ID
Here is a good post to understand joins
You can try distinct:
select distinct * from
tableA a,
tableB b
where a.id = b.id;
It will not give any duplicate tuples.
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 = ?
SQL:
WITH joined AS (
SELECT *
FROM table_a a
JOIN table_b b ON (a.a_id = b.a_id)
)
SELECT a_id
FROM joined
returns invalid identifier.
How can you select joined column when using WITH clause? I have tried aliases, prefixing and nothing worked. I know I can use:
WITH joined AS (
SELECT a.a_id
FROM table_a a
JOIN table_b b ON (a.a_id = b.a_id)
)
SELECT a_id
FROM joined
but I need this alias to cover all fields.
Only way I managed to meet this condition is using:
WITH joined AS (
SELECT a.a_id a_id_alias, a.*, b.*
FROM table_a a
JOIN table_b b ON (a.a_id = b.a_id)
)
SELECT a_id_alias
FROM joined
but it is not perfect solution...
You can use the effect of the USING clause when joining the tables.
When you join tables where the join columns have the same name (as it is the case with your example), the USING clause will return the join column only once, so the following works:
with joined as (
select *
from table_a a
join table_b b using (a_id)
)
select a_id
from joined;
SQLFiddle example: http://sqlfiddle.com/#!4/e7e099/2
I don't think you can do this without aliases. The result of the "joined" query has two fields, both named a_id. Unless you alias one (or both), as you did in your final query, the outer query has no idea which a_id you are referring to.
Why is your final query not a "perfect" solution?
You can probably use alias as below:
WITH JOINED AS (
SELECT A.A_ID A_A_ID, B.A_ID B_A_ID,
A.FIELD_NAME1 A_FIELDNAME1, A.FIELDNAME2 A_FIELDNAME2,A.FIELDNAME_N A_FIELDNAME_N,
B.FIELD_NAME1 B_FIELDNAME1, B.FIELDNAME2 B_FIELDNAME2,B.FIELDNAME_N B_FIELDNAME_N,
FROM TABLE_A A
JOIN TABLE_B B ON (A.A_ID = B.A_ID)
)
SELECT A_A_ID, B_A_ID
FROM JOINED
IT IS ALWAYS A GOOD PRACTICE TO AVOID USING SELECT *
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 );