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我在使用JDOQL(使用DataNucleus)进行子查询计数时遇到了问题。下面的查询JDOQL子查询计数问题
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)
下面的查询工作既不:
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()
什么是确保一个子查询的结果是不是空的正确方法?