Java 如何进行 JPQL 子查询？
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How do I do a JPQL SubQuery?
提问by ErVeY
It is possible to do the equivalent of this sql query in JPQL?
可以在 JPQL 中执行与此 sql 查询等效的操作吗？
SELECT *
FROM COUNTRIES c WHERE COUNTRY_ID IN (
SELECT DISTINCT COUNTRY_ID
FROM PORTS p
WHERE p.COUNTRY_ID = c.COUNTRY_ID AND STATE = 'A'
)
采纳答案by topchef
You need to test it with INand subquerysince both do work in JPQL (according to syntax reference they do work together). You may also look at MEMBER OF expressions.
您需要使用IN和子查询对其进行测试，因为两者都在 JPQL 中工作（根据语法参考，它们确实可以一起工作）。您还可以查看MEMBER OF 表达式。
But there is a better approach in my opinion. Such queries are called correlated sub-queries and one can always re-write them using EXISTS:
但我认为有更好的方法。此类查询称为相关子查询，并且始终可以使用 EXISTS 重写它们：
SELECT * FROM COUNTRIES c WHERE
EXISTS (
SELECT 'found' FROM PORTS p
WHERE p.COUNTRY_ID = c.COUNTRY_ID AND STATE = 'A'
)
JPQL supports EXISTS with subqueries.
JPQL 支持带有子查询的 EXISTS。
