I have several entities and want to do a join like this:
SELECT g FROM Gift g
LEFT JOIN Worker w ON g.receiver = w.person
WHERE ....
AND w.company = :companyId
The problem is that there's no direct connection between g.receiver who is a Person and w.person. I don't want to inner join them either, because a receiver of a gift may not be a worker of a company.
I had the same problem, but i didn't find any solution in JPQL, it looks like if you don't have a mapped relation, you can't perform a left join.
I solved the problem with 2 query and a join implemented by code.
Another solution is a native query.
Related
I need the JPQL in this format:
SELECT *
FROM Person p
LEFT JOIN Address a ON p.id = a.id AND a.flat = 100;
But when i run the code the query being slightly modified henceforth the output of data changed..
SELECT * FROM Person p LEFT JOIN Address a ON p.id = a.id where a.flat = 100;
I suppose you want to format the sql output.
So for hibernate, you can set hibernate.format_sql=true to well format the sql.
If you are using spring boot, you can config it via spring.jpa.properties.hibernate.format_sql=true simply.
JPQL does not allow joining to arbitrary other root objects, so you can't do that in JPQL; only allowing you to join along relations. Individual vendors may offer a vendor extension to allow joining across arbitrary roots but you then lose portability.
To provide more than that you have to post the actual JPA entities, and you haven't.
I want to join two tables together and add additional information from two other tables to the same columns in both queried tables. I've come up with the below code, which works, but I don't feel comfortable about having to add another JOIN clause for each table, as it would make the query substantially long if I wanted to join/add more things.
Is there a way to combine it, so that I can join additional tables only once (just use S and E aliases every time)?
SELECT
J.JobId,
J.StandardJobId,
S.JobName,
J.EngineerId,
E.EngineerName,
JF.JobId AS FollowUpJobId,
JF.StandardJobId AS FollowUpStandardJobId,
SF.JobName AS FollowUpJobName,
JF.EngineerId AS FollowUpEngineerId,
EF.EngineerName AS FollowUpEngineerName
FROM
Jobs J
INNER JOIN
Jobs JF
ON
J.FollowUpJobId = JF.JobId
INNER JOIN
StandardJobs S
ON
J.StandardJobId = S.StandardJobId
INNER JOIN
Engineers E
ON
E.EngineerId = J.EngineerId
INNER JOIN
StandardJobs SF
ON
SF.StandardJobId = JF.StandardJobId
INNER JOIN
Engineers EF
ON
EF.EngineerId = JF.EngineerId
One approach would be to use a Common Table Expression (CTE) - something like:
with cte as
(SELECT J.JobId,
J.StandardJobId,
S.JobName,
J.EngineerId,
E.EngineerName,
J.FollowUpJobId
FROM Jobs J
INNER JOIN StandardJobs S ON J.StandardJobId = S.StandardJobId
INNER JOIN Engineers E ON E.EngineerId = J.EngineerId)
SELECT O.*,
F.StandardJobId AS FollowUpStandardJobId,
F.JobName AS FollowUpJobName,
F.EngineerId AS FollowUpEngineerId,
F.EngineerName AS FollowUpEngineerName
FROM CTE AS O
JOIN CTE AS F ON O.FollowUpJobId = F.JobId
You can sort of do this with either a CTE (Common Table Expressions, the WITH clause) or a View:
;WITH Jobs_Extended As
(
SELECT j.*,
s.JobName,
E.EngineerName
FROM Jobs As j
JOIN StandardJobs As s ON s.StandardJobId = j.StandardJobId
JOIN Engineer As e ON e.EngineerId = j.EngineerId
)
SELECT
J.JobId,
J.StandardJobId,
J.JobName,
J.EngineerId,
J.EngineerName,
JF.JobId AS FollowUpJobId,
JF.StandardJobId AS FollowUpStandardJobId,
JF.JobName AS FollowUpJobName,
JF.EngineerId AS FollowUpEngineerId,
JF.EngineerName AS FollowUpEngineerName
FROM Jobs_Extended J
JOIN Jobs_Extended JF ON J.FollowUpJobId = JF.JobId
In this example the CTE Jobs_Extended becomes a defined alias for the relationship between the Jobs, Engineers and StandardJobs tables. Then once defined, you can use it multiple times in the query without having to redefine those interior relations.
You can do the same thing by change the WITH to a View, which will make the defined alias permannet in your database.
No, you cannot avoid JOINing related tables each time a separate reference is needed. The issue is that you are not working with the tables in a general sense but instead working with the specific rows of each table, even more specifically, just those rows that match the JOIN and WHERE conditions.
There is no way to specify the references to either StandardJobs or Engineers only once because you are needing to work with two rows from each table at the same time, at least in the given example.
However, depending on which direction you are wanting to go with "additional tables" (more references to Jobs or more lookups like StandardJobs and Engineers for the given 2 references of Jobs), the CTE construct shown by Mark is the probably the easiest / best way to abstract it. I posted this answer mainly to explain the issue at hand.
Should SQL Server yield the same results for both of the queries below? The primary difference is the condition being placed in the WHERE clause with the former, and with the latter being placed as a condition upon the join itself.
SELECT *
FROM cars c
INNER JOIN parts p
ON c.CarID = p.CarID
WHERE p.Desc LIKE '%muffler%'
SELECT *
FROM cars c
INNER JOIN parts p
ON c.CarID = p.CarID
AND p.Desc LIKE '%muffler%'
Thanks in advance for any help that I receive upon this!
For INNER JOINS it will make no difference to semantics or performance. Both will give the same plan. For OUTER JOINs it does make a difference though.
/*Will return all rows from cars*/
SELECT c.*
FROM cars c
LEFT JOIN parts p
ON c.CarID = p.CarID AND c.CarID <> c.CarID
/*Will return no rows*/
SELECT c.*
FROM cars c
LEFT JOIN parts p
ON c.CarID = p.CarID
WHERE c.CarID <> c.CarID
For inner joins the only issue is clarity. The JOIN condition should (IMO) only contain predicates concerned with how the two tables in the JOIN are related. Other unrelated filters should go in the WHERE clause.
For inner joins the two queries should yield exactly the same results. Are you seeing a difference?
Yes, they both get the same results. The difference is when the condition is checked, if during the join or afterwards.
The execution plan will be identical in your example. Next to the parse button should be the "Show execution plan" button. It will give you a clearer picture.
I think in a more complex query with many joins it can be an issue in efficiency, as stated above, before or after.
EDIT: sorry assuming your using sql server management studio.
My recommendation for this kind of situation would be:
put the JOIN condition (what establishes the "link" between the two tables) - and only that JOIN condition - after the JOIN operator
any additional conditions for one of the two joined tables belongs in the regular WHERE clause
So based on that, I would always recommend to write your query this way:
SELECT
(list of columns)
FROM
dbo.cars c
INNER JOIN
dbo.parts p ON c.CarID = p.CarID
WHERE
p.Desc LIKE 'muffler%'
It seem "cleaner" and more expressive that way - don't "hide" additional conditions behind a JOIN clause if they don't really belong there (e.g. help establish the link between the two tables being joined).
How can I produce something like this with Linq? I'm trying to work something out, this is related to my other post, but my distinct keeps coming back with more rows than expected
Add Conditional Join Dynamically with Linq
select distinct c.CompanyID, c.CompanyName from Company c
left join CompanyIndustry ci
on c.companyid = ci.companyid
left join CompanyService cs
on c.CompanyID = cs.CompanyID
where cs.ServiceID = 6 and ci.IndustryID = 4
If your companyID has more than one related industry or service, you'll get more than one row per company.
You should use GROUP BY Not distinct
I have a fairly conventional set of order entry tables divided by:
Orders
OrdersRows
OrdersRowsOptions
The record in OrderRowOptions is not created unless needed. When I create a set of joins like
select * from orders o
inner join OrdersRows r on r.idOrder = o.idOrder
inner join ordersrowsoptions ro on ro.idOrderRow = r.idOrderRow
where r.idProduct = [foo]
My full resultset is blank if no ordersrowsoptions records exist for the given product.
what's the correct syntax to return records even if no records exist at one of the join clauses?
thx
select * from orders o
inner join OrdersRows r on r.idOrder = o.idOrder
left join ordersrowsoptions ro on ro.idOrderRow = r.idOrderRow
where r.idProduct = [foo]
Of course you should not use select * in any query but especially never when doing a join. The repeated fields are just wasting server and network resources.
Since you seem unfamiliar with left joins, you probably also need to understand the concepts in this:
http://wiki.lessthandot.com/index.php/WHERE_conditions_on_a_LEFT_JOIN
LEFT JOIN / RIGHT JOIN.
Edit: yes, the following answer, given earlier, is correct:
select * from orders o
inner join OrdersRows r on r.idOrder = o.idOrder
left join ordersrowsoptions ro on ro.idOrderRow = r.idOrderRow
where r.idProduct = [foo]
LEFT JOIN (or RIGHT JOIN) are probably what you are looking for, depending on which side of the join no rows may appear.
Interesting, do you want to get all orders that have that product in them? The other post is correct that you have to use LEFT or RIGHT OUTER JOINS. But if you want to get entire orders that have that product then you'd need a more complex where clause.