I have this table:
and would like to convert it to the following:
Please help me, been stuck on it for way too long. Doesn't working for me using group by
WITH A as (SELECT id, a FROM XXX WHERE a is not null),
B as (SELECT id, b FROM XXX WHERE b is not null)
SELECT A.a, B.b, A.id FROM A
INNER JOIN B on A.id = B.id;
For this dataset, simple aggregation would do what you want:
select min(a) a, min(b) b, id
from mytable
group by id
This takes advantage of the fact that aggregate functions ignore null values; we could get the very same result with max() as we did with min().
I have a simple question on how to read the number of occurences of some values in a table B that references to a value in a table A. It's all explained better in the following example:
Let's say I have two simple tables, A with an attribute ID and B with an attribute ID that references A.ID; I use this code to find the number of occurences of a A.ID value into B:
SELECT A.ID, COUNT(*)
FROM A JOIN B ON A.ID = B.ID
GROUP BY A.ID
Is it possible to achieve the same result using something like the following code...
SELECT ID, -- SOMETHING --
FROM A
....
... using this subquery?
SELECT COUNT(*)
FROM B WHERE B.ID = A.ID
Thank you very much
I think you might be referring to a correlated subquery:
select a.id, (select count(1) from b where id=a.id) cnt from a;
The a.id term in the subquery binds with table a in the outer query.
How Can I translate the following SQL query to Criteria query:
Select A.TextProperty, B.TextProperty, Count(C.Id)
From A, B, C
Where A.Id In
(
Select A.Id, C.Id, Count(C.Id)
From A, C
Having Count(C.Id) > 1
)
I know the Where part is incorrect, but I need to find a way to get only the A.Id after the inner/Sub-query select statement is executed.
Is there any way to select only the A.Id property from the sub-query then apply the Where condition on it?!
Please help me figure this out!
I have a query like below:
select
a.id, a.title, a.description
from
my_table_name as a
where
a.id in (select id from another_table b where b.id = 1)
My question is, is there any way I can avoid the subquery in where clause and use it in from clause itself without compromising of performance?
Both of the answers given so far are incorrect in the general case (though the database may have unique constraints which ensure they are correct in a specific case)
If another_table might have multiple rows with the same id then the INNER JOIN will bring back duplicates that are not present in the IN version. Trying to remove them with DISTINCT can change the semantics if the columns from my_table_name themselves have duplicates.
A general rewrite would be
SELECT a.id,
a.title,
a.description
FROM my_table_name AS a
JOIN (SELECT DISTINCT id
FROM another_table
WHERE id = 1) AS b
ON b.id = a.id
The performance characteristics of this rewrite are implementation dependant.
You may use INNER JOIN as:
select
a.id, a.title, a.description
from
my_table_name as a INNER JOIN another_table as b ON (a.id = b.id and b.id = 1)
Or
select
a.id, a.title, a.description
from
my_table_name as a INNER JOIN another_table as b ON a.id = b.id
where b.id = 1
Both the queries may not return the same value for you. You may choose whatever works for you. Please use this as a starting point and not as a copy-paste code.
To express it as a join:
select distinct
a.id, a.title, a.description
from my_table_name as a
join another_table b on b.id = a.id
where b.id = 1
The use of distinct is to produce the same results in case another_table has the same id more than once so the same row doesn't get returned multiple times.
Note: if combinations of id, name and description in my_table_name are not unique, this query won't return such duplicates as the original query would.
To guarantee to produce the same results, you need to ensure that the id's in another_table is unique. To do this as a join:
select
a.id, a.title, a.description
from my_table_name as a
join (select distinct id from another_table) b on b.id = a.id
where b.id = 1
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