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  • Mybatis-Plus条件构造器select方法返回指定字段

    条件构造器select方法介绍

    根据业务需求,有时候只需要返回特定的几个数据表字段,我们通过条件构造器的select方法可以指定;

    还有一种情况,假如数据库字段很多的时候,我们要排除某几个字段,其他字段返回的时候,select方法也支持排除某些字段,查询其他的;

    最后还有一种情况,我们搞分组聚合函数的时候,可以使用select方法,返回聚合函数执行后的数据字段;

    实例

    实例一:查找薪水大于3500 名字里有“小”的 员工  (只显示编号和姓名)

    @Test
    public void selectByQueryWrapper7(){
        QueryWrapper<Employee> queryWrapper=new QueryWrapper();
        // QueryWrapper<Employee> queryWrapper2=Wrappers.<Employee>query();
        queryWrapper.select("id","name").gt("salary",3500).like("name","");
        List<Employee> employeeList = employeeMapper.selectList(queryWrapper);
        System.out.println(employeeList);
    }

    实例二:查找薪水大于3500 名字里有“小”的 员工  (排除出生日期和性别)

    @Test
    public void selectByQueryWrapper8(){
        QueryWrapper<Employee> queryWrapper=new QueryWrapper();
        // QueryWrapper<Employee> queryWrapper2=Wrappers.<Employee>query();
        queryWrapper
                 .select(Employee.class,fieldInfo->!fieldInfo.getColumn().equals("birthday")&&!fieldInfo.getColumn().equals("gender"))
                 .gt("salary",3500)
                 .like("name","");
        List<Employee> employeeList = employeeMapper.selectList(queryWrapper);
        System.out.println(employeeList);
    }

    实例三:查询每个部门的平均薪资

    sql实现:

    SELECT departmentId,AVG(salary) AS avg_salary FROM t_employee GROUP BY department_id;
    @Test
    public void selectByQueryWrapper9(){
        QueryWrapper<Employee> queryWrapper=new QueryWrapper();
        // QueryWrapper<Employee> queryWrapper2=Wrappers.<Employee>query();
        queryWrapper
                 .select("department_id","AVG(salary) AS avg_salary")
                 .groupBy("department_id");
        List<Employee> employeeList = employeeMapper.selectList(queryWrapper);
        System.out.println(employeeList);
    }

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    作者: java1234_小锋

    出处:https://www.cnblogs.com/java688/p/13594789.html

    版权:本站使用「CC BY 4.0」创作共享协议,转载请在文章明显位置注明作者及出处。

    ------------------------------------------------------------------------------------------------------------------------------

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  • 原文地址:https://www.cnblogs.com/java688/p/13594789.html
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