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我是 JDOQL 的新手,但遇到以下问题。我正在尝试获取部门的平均工资,然后选择平均工资高于某个值的部门。

Query averageSalaryByDep = pm.newQuery(Employee.class);
averageSalaryByDep.setResult("department, avg(salary)");
averageSalaryByDep.setGrouping("department");

Query qry = pm.newQuery(Department.class);
qry.setFilter("this.name == dep.name && averageSalary > 10000");
qry.declareVariables("Department dep, double averageSalary");
qry.addSubquery(averageSalaryByDep, "Department dep, double averageSalary", null);

我目前收到的错误消息:

javax.jdo.JDOUserException: Class name averageSalary could not be resolved
    at org.datanucleus.api.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException(NucleusJDOHelper.java:636)
    at org.datanucleus.api.jdo.JDOQuery.executeInternal(JDOQuery.java:391)
    at org.datanucleus.api.jdo.JDOQuery.execute(JDOQuery.java:216)
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1 回答 1

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子查询有一个变量名(并返回一个事物)。如果不确定某事,请输入单字符串查询的外观(以及生成的 SQL),然后它应该是清楚的。JDO 规范有一些有用的例子 IIRC

关于您想要检索的内容,我建议您查看更多类似的内容

Query averageSalarySubq = pm.newQuery(Employee.class);
averageSalarySubq.setResult("avg(salary)");
averageSalarySubq.setFilter("this.department = :outerDepartment");

Query qry = pm.newQuery(Department.class);
qry.setFilter("averageSalary > 10000");
qry.declareVariables("double averageSalary");
qry.addSubquery(averageSalarySubq, "double averageSalary", null, "this");

这相当于

SELECT FROM mydomain.Department WHERE 
    (SELECT AVG(e.salary) FROM mydomain.Employee e WHERE e.department = this) > 10000

因此子查询获得平均工资但加入外部查询部门。定义 SQL 将向您揭示这是否是您想要的,但无论哪种方式,子查询都是针对单个变量的

于 2017-04-01T10:33:50.033 回答