I need to join two tables in such way that in the output I have an UNION of:
INNER JOIN of matching records
CARTESIAN of those which does not match (excluding the records above, i.e. those that match)
Maybe this looks like a piece of cake, but I need to do it in an efficient way (for far more complex query than this below).
a: 1|2|3|5
b: 2|3|4|6
result: (2,2)|(3,3)|(1,4)|(1,6)|(5,4)|(5,6)
Any helpful tricks you could advise? (I work on SQL Server 2012)
Thanks!
I'd use a CTE to define the joined records, something like this:
WITH MatchedRows
AS
SELECT A.a, B.b FROM A a INNER JOIN B b ON A.a = B.b
SELECT MatchedRows.a, MatchedRows.b
FROM MatchedRows
UNION
SELECT A.a, B.b FROM A a, B b
WHERE A.a NOT IN (SELECT a FROM MatchedRows)
AND B.b NOT IN (SELECT b FROM MatchedRows)
You didn't say what the column names were, so just called them Col.
SELECT A.Col,
B.Col
FROM A
INNER JOIN B
on A.Col = B.Col
UNION ALL
SELECT A.Col,
B.Col
FROM A
CROSS JOIN B
WHERE A.Col NOT IN (SELECT B.Col FROM B)
AND B.Col NOT IN (SELECT A.Col FROM A)
Related
Suppose I issue a query like this:
SELECT a.x, b.y FROM a LEFT JOIN b ON b.id = a.id
I also want to know if a row from b is actually joined or there are just placeholder NULL values supplied by LEFTJOIN. I guess I can determine it comparing values of a.id and b.id in the result, but is there a way to do this in the query itself?
I.e. I'd want something like
SELECT a.x, b.y, b_is_actually_joined FROM a LEFT JOIN b ON b.id = a.id
where values in the column b_is_actually_joined are 1 or 0 (for example).
Just check for NULL b.id:
SELECT a.x, b.y, b.id IS NOT NULL AS b_is_actually_joined
FROM a
LEFT JOIN b ON b.id = a.id
For Oracle SQL you can use NVL2 function:
SELECT a.id, b.*, NVL2(b.id, 1, 0) AS b_is_actually_joined
FROM a
LEFT JOIN b ON b.id = a.id
SQL Fiddle
This should work in Ms Sql Server:
select CAST((coalesce(b.id, 0)) as bit) as b_is_actually_joined FROM a
LEFT JOIN b ON b.id = a.id
I am unaware of a standard SQL solution for this
I have 3 tables and i want to join two of them with a condition.
For exemple if i have table A, table B and Table C, i'd like to have JOIN AB or JOIN BC.
Does something like this exists ?
SELECT *
FROM B
(JOIN A
ON (B.b=A.id_a)
OR (B.b=A.id_b))
OR
(JOIN C
ON (B.b=C.id_a)
OR (B.b=C.id_b))
WHERE B.a=1001485422
You can do both joins at once
select *
from
b
left join
a on b.b in (a.id_a, a.id_b)
left join
c on b.b in (c.id_a, c.id_b)
where b.a = 1001485422
I have three queries with the same column count and structure, does Google BigQuery support union all? I know it supports union but I need it to merge the result of the query into one result.
I have tried:
SELECT *
FROM
(SELECT a.a AS a, a.b AS b, d.c AS c FROM table_a a JOIN table_d d on d.a = a.a),
(SELECT c.a AS a, c.b AS b, d.c AS c FROM table_c c JOIN table_d d on d.a = ca.a),
(SELECT b.a AS a, b.b AS b, d.c AS c FROM table_b b JOIN table_d d on d.a = b.a)
I get the following error:
Union results in ambiguous schema [d.c] is ambiguous and is aliasing multiple fields
Thanks For your help.
Must you know if the data are come from table a, b or c? If you don't need to know, you can try the following query:
select *
from
(select a, b
from table_a, table_b, table_c) as a
join
(select a, c
from table_d) as d
on a.a = d.a
Hi I have looked through the "Case with multiple columns" questions and don't see something the same as this so I think I should ask.
Basically I have two tables (both are the result of a subquery) which I want to join. They have the same column names. If I join them on their ids and SELECT * I get each row being something like this:
A.id, A.x, A.y, A.z, A.num, B.id, B.x, B.y, B.z, B.num
What I want is a way to only select the columns of the table with the lower value of num. So in this case the result table would always have 5 columns, id, x, y, z, num, and I don't care which table id, x, y, z, num came from after the fact. Also either table result is fine if they are equal.
SELECT CASE WHEN A.num < B.num THEN A.* ELSE B.* END FROM A JOIN B ON A.id=B.id
would be perfect but you can only return one column in a CASE statement, and I could use a CASE for every column but that seems so wasteful (there are 8 in each table in my actual database so I would have 8 CASE statements).
This is SQLite btw. Any help would be appreciated!
Edit for more info on A and B:
A and B come from Queries like this
SELECT "thought case statement might go here" FROM
(SELECT id, x, y, z, num FROM Table1 a JOIN Table2 b ON a.id=b.id AND (y BETWEEN (53348574-3593) AND (53348574+3593)) AND (z BETWEEN (-6259973-6027) AND (-6259973+6027)) JOIN Table3 c ON c.id= b.id GROUP BY a.id, c.r) A
JOIN
(SELECT id, x, y, z, num FROM Table1 a JOIN Table2 b ON a.id=b.id AND (y BETWEEN (53401007-3593) AND (53401007+3593)) AND (z BETWEEN (-6397286-6027) AND (-6397286+6027)) JOIN Table3 c ON c.id= b.id GROUP BY a.id, c.r ) B ON A.id=B.id
So it joins two tables, made based on geolocation if you're wondering why the big numbers, and needs to decide which of the tables to take its data from based on attributes of what it finds in either of the locations.
try
select A.id, A.x, A.y, A.z, A.num from A JOIN B ON A.id=B.id where a.num<b.num
union
select b.id, b.x, b.y, b.z, b.num from A JOIN B ON A.id=B.id where b.num<a.numhere
I don't know of any RDBMS supporting what you want. You will have to write 8 CASE statements. But why is it so wasteful? Or are you just lazy? :)
Edit:
See, when you write SELECT * ... what your RDBMS is doing is to query system tables (information_schema and so on) and get the list of columns in the table.
So when you write
SELECT CASE WHEN A.num < B.num THEN A.* ELSE B.* END ...
you basically write
SELECT CASE WHEN A.num < B.num THEN A.num, A.whatever, A.more, ... ELSE B.num, B.whatever, B.more... END FROM A JOIN B ON A.id=B.id
and this is unfortunately wrong syntax.
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