I need to implement sql query like:
SELECT * FROM (SELECT a FROM b WHERE a.z = 1) WHERE rownum <=1;
How can I write such statement with QueryDSL (I am not using JPA and JDO - only clean sql)?
Querydsl SQL emulates paging of all the supports databases, so you can write directly
query.from(a)
.where(a.z.eq(1))
.limit(1)
.list(a);
If you need to write this via a subquery then like this
query.from(
new SQLSubQuery().from(a).where(a.z.eq(1)).list(a).as(a))
.where(rownum.loe(1))
.list(a);
Related
I find that cosmos DB support get a distinct count using SQL like
select value count(1) from (SELECT distinct c.StoreId FROM c)
But with EF core, context.Model.FromSqlRaw(#join) does not support return a Raw type instead of dbset model. Is it possible to return a custom raw type in ef core?
Queries with an aggregate system function and a subquery with DISTINCT are only supported in specific SDK versions. For example, queries with the following shape are only supported in the below specific SDK versions:
SELECT COUNT(1) FROM (SELECT DISTINCT f.lastName FROM f)
https://learn.microsoft.com/en-us/azure/cosmos-db/sql/sql-query-keywords
I need to implement select from a nested query, for the sake of simplicity let it be:
select * from (select * from city) c
How can this be done using CriteriaQuery and Subquery?
You can't because (select * from city) is not an entity and CritieriaAPI queries on entities not on tables.
The only way would be to create a view for (select * from city) and map that view to an entity.
First, your syntax is not JPA compliant as mentioned previously, secondly, you must know that subqueries in JPQL are allowed only in WHERE and HAVING clauses. The same applies to Criteria queries. If you need the more powerful SQL subquery features then with JPA you have to use JPA provisions for native queries, or otherwise, use another type of JDBC library.
is it possible in QueryDsl to perform a subquery in the from clause?
I would like to do something like:
SELECT * FROM
(Select Ammount, Ammount*(.10) as TenPercent From Expense)
Where TenPercent > 1
The general problem I am trying to solve is using a field from the projection (in this case TenPercent and PlusTenPerceent) in the where clause which can only be solved by using subqueries in the from clause.
How do you express this in QueryDsl? JPAExpressions do not solve this because it can not be used in the JPAQuery.from() method.
Any input is welcome!
Spring DATA JPA support subquery in from ?
like
select * from (
select unique_id
from table_a
) as from_a
inner join table_b
on from_a.unique_id = table_b.unique_id
querydsl JPASubquery or Spring DATA criteria impossible?
I think it is noe possible.
in other way. you use JPAExpressions. it will be serching for subquery in query dsl.
But i aleardy user that subQuery that are result only one table.
I wrote the following query for MySQL:
SELECT subquery.t1_column1,
subquery.t2_id,
MAX(subquery.val)
FROM (
SELECT t1.column1 as t1_column1,
t1.id_t2 AS t2_id,
count(1) AS val
FROM table1 t1
INNER JOIN table2 t2
ON t2.id = t1.id_t2
GROUP BY t1.id_t2
) subquery
GROUP BY t1_column1
And I'd like to translate it into JPA (JPQL or criteria query).
I don't know how to make this max(count) thing, and JPA doesn't seem to like the SELECT FROM SELECT...
If anyone has an idea other than native queries (I'll do it for now), it would be great.
I haven't checked tha JPA specification, but given that the Hibernate documentation says
Note that HQL subqueries can occur only in the select or where
clauses.
I very much doubt that your query can be transformed in a valid JPQL query.
You'll have to keep using this native SQL query.
JPA 2.0 JPQL does not support sub-selects in the from clause. You may want to try to rewrite your query, or use a native SQL query.
EclipseLink 2.4 will support sub-selects in the FROM clause,
see,
http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Querying/JPQL#Sub-selects_in_FROM_clause