我在使用 JDOQL(使用 DataNucleus)时遇到子查询计数问题。以下查询
SELECT this.price
FROM com.mysema.query.jdo.test.domain.Product
WHERE (SELECT count(other)
FROM com.mysema.query.jdo.test.domain.Product other
WHERE other.price > this.price) > a1
PARAMETERS java.lang.Long a1
导致异常
javax.jdo.JDOUserException: Cannot perform operation ">" on SubqueryExpression "(SELECT COUNT("OTHER".PRODUCT_ID) FROM PRODUCT "OTHER" WHERE "OTHER".PRICE > THIS.PRICE)" and IntegerLiteral "?"
at org.datanucleus.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException(NucleusJDOHelper.java:390)
at org.datanucleus.jdo.JDOQuery.executeWithArray(JDOQuery.java:321)
以下查询均无效:
SELECT this.price
FROM com.mysema.query.jdo.test.domain.Product
WHERE !(SELECT other
FROM com.mysema.query.jdo.test.domain.Product other
WHERE other.price > this.price).isEmpty()
确保子查询结果不为空的正确方法是什么?