I'm using EntityManager ("em") and creating a query using the method "createQuery", but it changes my query, If I use the method "createNativeQuery" it works fine, but than I can't add a list to parameters.
String query = " SELECT t0.id FROM Movie t0, Tagged t1, Tag t2 "
+ " WHERE t2.id = t1.tagfk AND t1.moviefk = t0.id AND t2.name in :tagList "
+ " GROUP BY t0.id HAVING count(distinct t2.id) = :size "
+ " ORDER BY count(t1) DESC, t0.popularity DESC";
Query q = em.createQuery(query, Integer.class);
q.setParameter("tagList", tagList);
q.setParameter("size", tagList.size());
q.setMaxResults(20);
result = (List<Integer>)q.getResultList();
The problem here is, when I print the query
System.out.println(q);
I got
SELECT t0.ID AS a1 FROM MOVIE t0, TAG t2, TAGGED t1 WHERE (((t2.ID = t1.TAGFK) AND
(t1.MOVIEFK = t0.ID)) AND (t2.NAME IN ?)) GROUP BY t0.ID
HAVING (COUNT(DISTINCT(t0.ID)) = ?) ORDER BY COUNT(t1.ID) DESC, t0.POPULARITY DESC LIMIT ? OFFSET ?"))
If you look closer, the:
HAVING count(distinct t2.id) = :size
became
HAVING (COUNT(DISTINCT(t0.ID)) = ?)
And obvious I got wrong result, it is checking the wrong table.
Is it a bug or I'm doing something wrong? I can't find why it is happening. thanks.
I solved it doing the follow:
First:
Update from JPA 2.0.X to 2.1.X
Second:
In the HAVING clause I added the column used in the SELECT and GROUP BY with a statement that doesn't interfere with anything:
HAVING t0.id IS NOT NULL AND count(distinct t2.id) = :size
The solution above does not work on 2.0.X, it will result in:
HAVING (COUNT(DISTINCT(t0.ID)) = ?) AND (COUNT(DISTINCT(t0.ID)) = ?)
weird!!!
I'm using Eclipse Link, I forgot to mention that.
It just works, but still, I'm not happy with the HAVING parser on JPA, it needs improvement.
Related
For school I needed to get all players who never played a match for the team with number 1. So I thought I would look for all players who played a match for the team with number 1 in a subquery. This is my subquery:
select distinct s.spelersnr, naam
from spelers s inner join wedstrijden w on (s.spelersnr = w.spelersnr and teamnr = 1)
Now to extract the players who never played a match for team 1 I thought I could use the "NOT EXISTS" operator. My query then looked like this:
select spelersnr, naam
from spelers
where not exists (select distinct s.spelersnr, naam
from spelers s inner join wedstrijden w on (s.spelersnr = w.spelersnr and teamnr = 1))
order by naam, spelersnr
But this query didn't return the result I needed (in fact it didn't return anything). Then I tried this query:
select spelersnr, naam
from spelers
where (spelersnr, naam) not in (select distinct s.spelersnr, naam
from spelers s inner join wedstrijden w on (s.spelersnr = w.spelersnr and teamnr = 1))
order by naam, spelersnr
This query returned the result I needed, but now I don't really understand the difference between "NOT EXISTS" and "NOT IN".
You where close, the difference between the NOT EXISTS and NOT IN is how the SQL is executed, using NOT IN will be much slower (obviously this depends on the size of the data sets involved) because it compares each row to each of the items in the clause.
in contrast EXISTS or NOT EXISTS does a lookup for the single row based on a a contextual where clause.
All that's missing in you example is the WHERE clause in the EXISTS
select spelersnr, naam
from spelers as sp
where not exists (select 1
from spelers s inner join wedstrijden w on (s.spelersnr = w.spelersnr and teamnr = 1)
where sp.spelersnr = s.spelersnr and sp.naam = s.naam)
order by naam, spelersnr
Hope this helps :)
In SQL Server, I know for sure that the following query;
SELECT things.*
FROM things
LEFT OUTER JOIN (
SELECT thingreadings.thingid, reading
FROM thingreadings
INNER JOIN things on thingreadings.thingid = things.id
ORDER BY reading DESC LIMIT 1) AS readings
ON things.id = readings.thingid
WHERE things.id = '1'
Would join against thingreadings only once the WHERE id = 1 had restricted the record set down. It left joins against just one row. However in order for performance to be acceptable in postgres, I have to add the WHERE id= 1 to the INNER JOIN things on thingreadings.thingid = things.id line too.
This isn't ideal; is it possible to force postgres to know that what I am joining against is only one row without explicitly adding the WHERE clauses everywhere?
An example of this problem can be seen here;
I am trying to recreate the following query in a more efficient way;
SELECT things.id, things.name,
(SELECT thingreadings.id FROM thingreadings WHERE thingid = things.id ORDER BY id DESC LIMIT 1),
(SELECT thingreadings.reading FROM thingreadings WHERE thingid = things.id ORDER BY id DESC LIMIT 1)
FROM things
WHERE id IN (1,2)
http://sqlfiddle.com/#!15/a172c/2
Not really sure why you did all that work. Isn't the inner query enough?
SELECT t.*
FROM thingreadings tr
INNER JOIN things t on tr.thingid = t.id AND t.id = '1'
ORDER BY tr.reading DESC
LIMIT 1;
sqlfiddle demo
When you want to select the latest value for each thingID, you can do:
SELECT t.*,a.reading
FROM things t
INNER JOIN (
SELECT t1.*
FROM thingreadings t1
LEFT JOIN thingreadings t2
ON (t1.thingid = t2.thingid AND t1.reading < t2.reading)
WHERE t2.thingid IS NULL
) a ON a.thingid = t.id
sqlfiddle demo
The derived table gets you the record with the most recent reading, then the JOIN gets you the information from things table for that record.
The where clause in SQL applies to the result set you're requesting, NOT to the join.
What your code is NOT saying: "do this join only for the ID of 1"...
What your code IS saying: "do this join, then pull records out of it where the ID is 1"...
This is why you need the inner where clause. Incidentally, I also think Filipe is right about the unnecessary code.
I have a query as
return Connection.db.Fetch<Issue, Condition , Result , Status>(
"SELECT * FROM Issue I, Condition C, Result R, Status S " +
"LEFT JOIN Issue ON Condition .ID = Issue.ConditionID" +
"LEFT JOIN Issue ON Result.ID = Issue.ResultID" +
"LEFT JOIN Issue ON Status.ID = Issue.StatusID " +
"WHERE Issue.ID= "+ issueId);
which is giving the error message:
The multi-part identifier "Condition.ID" could not be bound.
The objects "Issue" and "Issue" in the FROM clause have the same exposed names. Use correlation names to distinguish them.
What is worng with the above?
You're joining to Issue table several times, but never use aliases. This is especially a problem because you've added the same table to FROM part of your SELECT clause. Always use aliases in joins. It's the safest way.
So whenever you said Issue.ID query engine could not resolve to which one you're referring. Is it to the one in FROM part or the one in JOIN part.
Try out this code:
return Connection.db.Fetch<Issue, Condition , Result , Status>(
"SELECT * FROM Issue I, Condition C, Result R, Status S " +
"LEFT JOIN Issue i1 ON C.ID = i1.ConditionID" +
"LEFT JOIN Issue i2 ON R.ID = i2.ResultID" +
"LEFT JOIN Issue i3 ON S.ID = i3.StatusID " +
"WHERE I.ID = " + issueId);
And apart from that I strongly suggest you use parameters instead of string concatenation:
return Connection.db.Fetch<Issue, Condition , Result , Status>(
"SELECT * FROM Issue I, Condition C, Result R, Status S " +
"LEFT JOIN Issue i1 ON C.ID = i1.ConditionID" +
"LEFT JOIN Issue i2 ON R.ID = i2.ResultID" +
"LEFT JOIN Issue i3 ON S.ID = i3.StatusID " +
"WHERE I.ID = #0", issueId); // see the change in this line
After some thought this is actually invalid SQL query
The problem that you're having is not PetaPoco related at all. You've actually written an invalid SQL query. If you'd run this same statement in SSMS you'd get the same error and that's because your query is interpreted as:
SELECT * FROM Issue I, Condition C, Result R,
(Status S
LEFT JOIN Issue i1
ON C.ID = i1.ConditionID
LEFT JOIN Issue i2
ON R.ID = i2.ResultID
LEFT JOIN Issue i3
ON S.ID = i3.StatusID
)
WHERE I.ID = x;
And that's the main reason why the first two joins fail. The last one is the only one that works, because it sees both tables. You probably thought that your select makes a result of those tables and then joins as in:
SELECT * FROM (Issue I, Condition C, Result R, Status S)
LEFT JOIN ...
But that is not the case.
Depending on what kind of results you want (you may end up with a large result set the way that you're doing it) you will have to rewrite your query to a different form and possibly omit the multi table list in your FROM part.
I am trying to write the following SQL query as a JPA query. The SQL query works (MySQL database) but I don't know how to translate it. I get a error token right after the first FROM. There are probably other errors here too because I was not able to find any guides on how to do sub-queries in the from part, aliasing and so on.
SQL query
SELECT tbl.* from (
SELECT u.*, COUNT(u.id) AS question_count FROM app_user AS u
INNER JOIN question AS q ON u.id = q.user_id GROUP BY u.id
) AS tbl ORDER BY tbl.question_count DESC LIMIT 10;
JPA query:
SELECT tbl FROM (SELECT u, COUNT(u.id) question_count FROM User u
INNER JOIN u.questions q ON u.id = q.user_id GROUP BY u.id) tbl
ORDER BY tbl.question_count LIMIT 10")
I can't test this with anything right now, but something along the lines of:
final String queryStr = "SELECT u, COUNT(u.id) FROM User u, Questions q WHERE u.id = q.user_id GROUP BY u.id ORDER BY COUNT(u.id) DESC";
Query query = em().createQuery(queryStr);
query.setMaxResults(10);
List<Object[]> results = query.getResultList(); //Index [0] will contain the User-object, [1] will contain Long with result of COUNT(u.id)
I want to write a lttl complicated query in JPQL where i access a OneToMany Join table. I get QuerySyntaxException: Pan_PanRes is not mapped.
QUERY -
query = "SELECT p FROM Pan p WHERE p.id IN " +
"(SELECT p_id FROM Pan_PanRes p_prs WHERE prs_id IN " +
"(SELECT r.id FROM PRS r where r.pant = :pant))"+
" ORDER BY pr.clD"
i tried implementing this concept in MYSQL. It works fine. So i know i am not calling the join table in right way. How should it be called then?
I would like to add MYSQL statement which works fine -
mysql> select * from pan where id not in
(select pan_id from pan_panres where panres_id in
(select id from panres where pant_id = 3));
Thanks...
Solved it myself -
query = "SELECT p FROM Pan p WHERE p.id IN " +
"(SELECT p.id FROM p.panRes prs WHERE id IN " +
"(SELECT r.id FROM PanRes r where r.pant = :pant))"+
" ORDER BY pr.clD"
Where panRes is the oneToMany variable name i have used in Pan Class.