9. coo---prolaris

发布于：2022-12-12 ⋅ 阅读:(432) ⋅ 点赞:(0)

47 子查询课后练习

子查询的编码技巧（或步骤）：①从里网往外写；②从外往里写
如何选择？
①如果子查询相对较简单。建议从外往里写，一旦子查询结构结构较复杂，建议从里往外写。
②如果是相关子查询的话，通常都是从外往里写
1. 查询和 Zlotkey 相同部门的员工姓名和工资  
SELECT last_name, salary FROM employees 
    WHERE department_id = ( SELECT department_id FROM employees WHERE last_name = 'Zlotkey');

2.查询工资比公司平均工资高的员工的员工号，姓名和工资

SELECT employee_id, last_name, salary 
    FROM employees WHERE salary > ( SELECT AVG(salary) FROM employees );
3.选择工资大于所有JOB_ID = 'SA_MAN'的员工的工资的员工的last_name, job_id, salary 
SELECT last_name,job_id,salary 
    FROM employees WHERE salary > ALL ( SELECT salary FROM employees WHERE job_id = 'SA_MAN' );
4.查询和姓名中包含字母u的员工在相同部门的员工的员工号和姓名 
SELECT employee_id, last_name 
    FROM employees WHERE department_id = ANY( SELECT DISTINCT department_id FROM employees WHERE last_name LIKE '%u%' );
5.查询在部门的location_id为1700的部门工作的员工的员工号 
SELECT employee_id FROM employees 
    WHERE department_id IN ( SELECT department_id FROM departments WHERE location_id = 1700 );

6.查询管理者是King的员工姓名和工资 

SELECT last_name, salary 
    FROM employees WHERE manager_id IN ( SELECT employee_id FROM employees WHERE last_name = 'King' );

7.查询工资最低的员工信息: last_name, salary 

SELECT last_name,salary FROM employees 
    WHERE salary = ( SELECT MIN(salary) FROM employees );
8.查询平均工资最低的部门信息 
方式一： 
SELECT * FROM departments 
    WHERE department_id = ( SELECT department_id 
        FROM employees 
            GROUP BY department_id 
                HAVING AVG(salary) = ( SELECT MIN(dept_avgsal) 
                    FROM (SELECT AVG(salary) dept_avgsal FROM employees GROUP BY department_id ) avg_sal ) ); 
方式二： 
SELECT * FROM departments 
    WHERE department_id = ( SELECT department_id       
        FROM employees GROUP BY department_id 
            HAVING AVG(salary) <= ALL( SELECT AVG(salary) avg_sal FROM employees GROUP BY department_id ) ); 
方式三： 
SELECT * FROM departments 
    WHERE department_id = (SELECT department_id 
        FROM employees GROUP BY department_id 
            HAVING AVG(salary) = ( SELECT AVG(salary) avg_sal FROM employees GROUP BY department_id ORDER BY avg_sal LIMIT 0,1 ) ) ;
方式四： 
SELECT d.* FROM departments d,( SELECT department_id,AVG(salary) avg_sal 
    FROM employees GROUP BY department_id 
        ORDER BY avg_sal LIMIT 0,1) dept_avg_sal 
            WHERE d.department_id = dept_avg_sal.department_id;

9.查询平均工资最低的部门信息和该部门的平均工资（相关子查询） 

方式一： 
SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.department_id) avg_sal 
    FROM departments d WHERE department_id = ( SELECT department_id 
        FROM employees GROUP BY department_id 
            HAVING AVG(salary) = ( SELECT MIN(dept_avgsal) 
                FROM (SELECT AVG(salary) dept_avgsal FROM employees 
                    GROUP BY department_id ) avg_sal ) );
方式二： 
SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.`department_id`) avg_sal 
    FROM departments d WHERE department_id = ( SELECT department_id 
        FROM employees GROUP BY department_id 
            HAVING AVG(salary) <= ALL( SELECT AVG(salary) avg_sal FROM employees GROUP BY department_id ) );

#方式三： 
SELECT d.*,(SELECT AVG(salary) FROM employees WHERE department_id = d.department_id) avg_sal 
    FROM departments d WHERE department_id = ( SELECT department_id 
        FROM employees GROUP BY department_id 
            HAVING AVG(salary) = ( SELECT AVG(salary) avg_sal 
                FROM employees GROUP BY department_id ORDER BY avg_sal LIMIT 0,1 ) );

#方式四： 
SELECT d.*,dept_avg_sal.avg_sal FROM departments d,( SELECT department_id,AVG(salary) avg_sal 
    FROM employees GROUP BY department_id 
        ORDER BY avg_sal LIMIT 0,1) dept_avg_sal 
            WHERE d.department_id = dept_avg_sal.department_id;
10.查询平均工资最高的 job 信息 
方式一： 
SELECT * FROM jobs WHERE job_id = ( SELECT job_id 
    FROM employees GROUP BY job_id 
        HAVING AVG(salary) = ( SELECT MAX(avg_sal) FROM(SELECT AVG(salary) avg_sal FROM employees GROUP BY job_id ) job_avgsal ) );

#方式二： 
SELECT * FROM jobs WHERE job_id = ( SELECT job_id 
    FROM employees GROUP BY job_id 
        HAVING AVG(salary) >= ALL( SELECT AVG(salary) FROM employees GROUP BY job_id ) );

方式三： 
SELECT * FROM jobs WHERE job_id = ( SELECT job_id 
    FROM employees GROUP BY job_id 
        HAVING AVG(salary) = ( SELECT AVG(salary) avg_sal 
            FROM employees GROUP BY job_id ORDER BY avg_sal DESC LIMIT 0,1 ) );

方式四： 
SELECT j.* FROM jobs j,( SELECT job_id,AVG(salary) avg_sal 
    FROM employees GROUP BY job_id 
        ORDER BY avg_sal DESC LIMIT 0,1 ) job_avg_sal 
            WHERE j.job_id = job_avg_sal.job_id;
11.查询平均工资高于公司平均工资的部门有哪些? 
SELECT department_id FROM employees 
    WHERE department_id IS NOT NULL 
        GROUP BY department_id 
            HAVING AVG(salary) > ( SELECT AVG(salary) FROM employees );
12.查询出公司中所有 manager 的详细信息 
方式1： 子查询
SELECT employee_id,last_name,salary 
    FROM employees 
        WHERE employee_id IN ( SELECT DISTINCT manager_id FROM employees );

方式2： 自连接
SELECT DISTINCT e1.employee_id, e1.last_name, e1.salary 
    FROM employees e1 JOIN employees e2 where/on e1.employee_id = e2.manager_id;

方式3： 使用EXISTS
SELECT employee_id, last_name, salary 
    FROM employees e1 
        WHERE EXISTS ( SELECT * FROM employees e2 WHERE e2.manager_id = e1.employee_id);
13.各个部门中 最高工资中最低的那个部门的 最低工资是多少? 
方式1：
SELECT MIN(salary) FROM employees 
    WHERE department_id = ( SELECT department_id 
        FROM employees GROUP BY department_id 
            HAVING MAX(salary) = ( SELECT MIN(max_sal) 
                FROM ( SELECT MAX(salary) max_sal 
                    FROM employees GROUP BY department_id) dept_max_sal ) );

验证：SELECT * FROM employees WHERE department_id = 10;

方式2: 
SELECT MIN(salary) FROM employees 
    WHERE department_id = ( SELECT department_id 
        FROM employees GROUP BY department_id 
            HAVING MAX(salary) <= ALL( SELECT MAX(salary) max_sal 
                FROM employees GROUP BY department_id ) );

方式3： 
SELECT MIN(salary) FROM employees 
    WHERE department_id = ( SELECT department_id 
        FROM employees GROUP BY department_id 
            HAVING MAX(salary) = ( SELECT MAX(salary) max_sal 
                FROM employees GROUP BY department_id 
                    ORDER BY max_sal LIMIT 0,1 ) )

方式4： 
SELECT employee_id,MIN(salary) 
    FROM employees e,(SELECT department_id,MAX(salary) max_sal 
        FROM employees GROUP BY department_id 
            ORDER BY max_sal LIMIT 0,1) dept_max_sal 
                WHERE e.department_id = dept_max_sal.department_id
14.查询平均工资最高的部门的 manager 的详细信息: last_name, department_id, email, salary 
方式1： 
SELECT employee_id,last_name, department_id, email, salary 
    FROM employees WHERE employee_id IN ( SELECT DISTINCT manager_id 
        FROM employees WHERE department_id = ( SELECT department_id 
            FROM employees GROUP BY department_id 
                HAVING AVG(salary) = ( SELECT MAX(avg_sal) 
                    FROM( SELECT AVG(salary) avg_sal 
                        FROM employees GROUP BY department_id ) dept_sal ) ) );

方式2： 
SELECT employee_id,last_name, department_id, email, salary 
    FROM employees WHERE employee_id IN (SELECT DISTINCT manager_id 
        FROM employees WHERE department_id = ( SELECT department_id 
            FROM employees e GROUP BY department_id 
                HAVING AVG(salary)>=ALL( SELECT AVG(salary) FROM employees 
                    GROUP BY department_id ) ) );

方式3： 
SELECT * FROM employees 
    WHERE employee_id IN ( SELECT DISTINCT manager_id 
        FROM employees e,( SELECT department_id,AVG(salary) avg_sal 
            FROM employees GROUP BY department_id 
                ORDER BY avg_sal DESC LIMIT 0,1) dept_avg_sal 
                    WHERE e.department_id = dept_avg_sal.department_id );
15. 查询部门的部门号，其中不包括job_id是"ST_CLERK"的部门号 
方法1： 
SELECT department_id FROM departments d 
    WHERE department_id NOT IN ( SELECT DISTINCT department_id 
        FROM employees WHERE job_id = 'ST_CLERK' );

方法2： SELECT department_id FROM departments d 
    WHERE NOT EXISTS ( SELECT * FROM employees e 
        WHERE d.`department_id` = e.`department_id` AND job_id = 'ST_CLERK' );
16. 选择所有没有管理者的员工的 last_name 
SELECT last_name FROM employees e1 
    WHERE NOT EXISTS ( SELECT * FROM employees e2 
        WHERE e1.manager_id = e2.employee_id );
17．查询员工号、姓名、雇用时间、工资，其中员工的管理者为 'De Haan' 
方式1： 
SELECT employee_id, last_name, hire_date, salary 
    FROM employees WHERE manager_id = ( SELECT employee_id 
        FROM employees WHERE last_name = 'De Haan' );

方式2： 
SELECT employee_id, last_name, hire_date, salary 
    FROM employees e1 WHERE EXISTS ( SELECT * FROM employees e2 
        WHERE e2.`employee_id` = e1.manager_id AND e2.last_name = 'De Haan' );
18.查询各部门中工资比本部门平均工资高的员工的员工号, 姓名和工资（相关子查询）
  
方式1：相关子查询 
SELECT employee_id,last_name,salary 
    FROM employees e1 WHERE salary > ( SELECT AVG(salary) 
        FROM employees e2 WHERE e2.department_id = e1.`department_id` );

方式2:在from中声明子查询
SELECT employee_id,last_name,salary 
    FROM employees e1, (SELECT department_id,AVG(salary) avg_sal 
        FROM employees e2 GROUP BY department_id ) dept_avg_sal 
            WHERE e1.`department_id` = dept_avg_sal.department_id 
                AND e1.`salary` > dept_avg_sal.avg_sal;
19.查询每个部门下的部门人数大于 5 的部门名称（相关子查询） 
SELECT department_name,department_id 
    FROM departments d WHERE 5 < ( SELECT COUNT(*) FROM employees e 
        WHERE d.`department_id` = e.`department_id` );
20.查询每个国家下的部门个数大于 2 的国家编号（相关子查询） 
SELECT country_id FROM locations l 
    WHERE 2 < ( SELECT COUNT(*) FROM departments d 
        WHERE l.`location_id` = d.`location_id` );

------------------------Executor-----------------------------

package com.itheima.mybatis.sqlsession.utils;

import com.itheima.mybatis.sqlsession.mappers.Mapper;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;

/**
 * @author 黑马程序员
 * @Company http://www.ithiema.com
 * 负责执行SQL语句，并且封装结果集
 */
public class Executor {

    public <E> List<E> selectList(Mapper mapper, Connection conn) {
        PreparedStatement pstm = null;
        ResultSet rs = null;
        try {
            //1.取出mapper中的数据
            String queryString = mapper.getQueryString();//select * from user
            String resultType = mapper.getResultType();//com.itheima.domain.User
            Class domainClass = Class.forName(resultType);
            //2.获取PreparedStatement对象
            pstm = conn.prepareStatement(queryString);
            //3.执行SQL语句，获取结果集
            rs = pstm.executeQuery();
            //4.封装结果集
            List<E> list = new ArrayList<E>();//定义返回值
            while(rs.next()) {
                //实例化要封装的实体类对象
                E obj = (E)domainClass.newInstance();

                //取出结果集的元信息：ResultSetMetaData
                ResultSetMetaData rsmd = rs.getMetaData();
                //取出总列数
                int columnCount = rsmd.getColumnCount();
                //遍历总列数
                for (int i = 1; i <= columnCount; i++) {
                    //获取每列的名称，列名的序号是从1开始的
                    String columnName = rsmd.getColumnName(i);
                    //根据得到列名，获取每列的值
                    Object columnValue = rs.getObject(columnName);
                    //给obj赋值：使用Java内省机制（借助PropertyDescriptor实现属性的封装）
                    PropertyDescriptor pd = new PropertyDescriptor(columnName,domainClass);//要求：实体类的属性和数据库表的列名保持一种
                    //获取它的写入方法
                    Method writeMethod = pd.getWriteMethod();
                    //把获取的列的值，给对象赋值
                    writeMethod.invoke(obj,columnValue);
                }
                //把赋好值的对象加入到集合中
                list.add(obj);
            }
            return list;
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            release(pstm,rs);
        }
    }


    private void release(PreparedStatement pstm,ResultSet rs){
        if(rs != null){
            try {
                rs.close();
            }catch(Exception e){
                e.printStackTrace();
            }
        }

        if(pstm != null){
            try {
                pstm.close();
            }catch(Exception e){
                e.printStackTrace();
            }
        }
    }
}
 

---------------------------XMLConfigBuilder----------------------------

package com.itheima.mybatis.sqlsession.utils;

import com.itheima.mybatis.annotations.Select;
import com.itheima.mybatis.io.Resources;
import com.itheima.mybatis.sqlsession.Configuration;
import com.itheima.mybatis.sqlsession.defaults.DefaultSqlSession;
import com.itheima.mybatis.sqlsession.mappers.Mapper;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author 黑马程序员
 * @Company http://www.ithiema.com
 *  用于解析配置文件
 */
public class XMLConfigBuilder {

    /**
     * 解析主配置文件，把里面的内容填充到DefaultSqlSession所需要的地方
     * 使用的技术：
     *      dom4j+xpath
     */
    public static Configuration loadConfiguration(InputStream config){
        try{
            //定义封装连接信息的配置对象（mybatis的配置对象）
            Configuration cfg = new Configuration();

            //1.获取SAXReader对象
            SAXReader reader = new SAXReader();
            //2.根据字节输入流获取Document对象
            Document document = reader.read(config);
            //3.获取根节点
            Element root = document.getRootElement();
            //4.使用xpath中选择指定节点的方式，获取所有property节点
            List<Element> propertyElements = root.selectNodes("//property");
            //5.遍历节点
            for(Element propertyElement : propertyElements){
                //判断节点是连接数据库的哪部分信息
                //取出name属性的值
                String name = propertyElement.attributeValue("name");
                if("driver".equals(name)){
                    //表示驱动
                    //获取property标签value属性的值
                    String driver = propertyElement.attributeValue("value");
                    cfg.setDriver(driver);
                }
                if("url".equals(name)){
                    //表示连接字符串
                    //获取property标签value属性的值
                    String url = propertyElement.attributeValue("value");
                    cfg.setUrl(url);
                }
                if("username".equals(name)){
                    //表示用户名
                    //获取property标签value属性的值
                    String username = propertyElement.attributeValue("value");
                    cfg.setUsername(username);
                }
                if("password".equals(name)){
                    //表示密码
                    //获取property标签value属性的值
                    String password = propertyElement.attributeValue("value");
                    cfg.setPassword(password);
                }
            }
            //取出mappers中的所有mapper标签，判断他们使用了resource还是class属性
            List<Element> mapperElements = root.selectNodes("//mappers/mapper");
            //遍历集合
            for(Element mapperElement : mapperElements){
                //判断mapperElement使用的是哪个属性
                Attribute attribute = mapperElement.attribute("resource");
                if(attribute != null){
                    System.out.println("使用的是XML");
                    //表示有resource属性，用的是XML
                    //取出属性的值
                    String mapperPath = attribute.getValue();//获取属性的值"com/itheima/dao/IUserDao.xml"
                    //把映射配置文件的内容获取出来，封装成一个map
                    Map<String,Mapper> mappers = loadMapperConfiguration(mapperPath);
                    //给configuration中的mappers赋值
                    cfg.setMappers(mappers);
                }else{
                    System.out.println("使用的是注解");
                    //表示没有resource属性，用的是注解
                    //获取class属性的值
                    String daoClassPath = mapperElement.attributeValue("class");
                    //根据daoClassPath获取封装的必要信息
                    Map<String,Mapper> mappers = loadMapperAnnotation(daoClassPath);
                    //给configuration中的mappers赋值
                    cfg.setMappers(mappers);
                }
            }
            //返回Configuration
            return cfg;
        }catch(Exception e){
            throw new RuntimeException(e);
        }finally{
            try {
                config.close();
            }catch(Exception e){
                e.printStackTrace();
            }
        }

    }

    /**
     * 根据传入的参数，解析XML，并且封装到Map中
     * @param mapperPath    映射配置文件的位置
     * @return  map中包含了获取的唯一标识（key是由dao的全限定类名和方法名组成）
     *          以及执行所需的必要信息（value是一个Mapper对象，里面存放的是执行的SQL语句和要封装的实体类全限定类名）
     */
    private static Map<String,Mapper> loadMapperConfiguration(String mapperPath)throws IOException {
        InputStream in = null;
        try{
            //定义返回值对象
            Map<String,Mapper> mappers = new HashMap<String,Mapper>();
            //1.根据路径获取字节输入流
            in = Resources.getResourceAsStream(mapperPath);
            //2.根据字节输入流获取Document对象
            SAXReader reader = new SAXReader();
            Document document = reader.read(in);
            //3.获取根节点
            Element root = document.getRootElement();
            //4.获取根节点的namespace属性取值
            String namespace = root.attributeValue("namespace");//是组成map中key的部分
            //5.获取所有的select节点
            List<Element> selectElements = root.selectNodes("//select");
            //6.遍历select节点集合
            for(Element selectElement : selectElements){
                //取出id属性的值      组成map中key的部分
                String id = selectElement.attributeValue("id");
                //取出resultType属性的值  组成map中value的部分
                String resultType = selectElement.attributeValue("resultType");
                //取出文本内容            组成map中value的部分
                String queryString = selectElement.getText();
                //创建Key
                String key = namespace+"."+id;
                //创建Value
                Mapper mapper = new Mapper();
                mapper.setQueryString(queryString);
                mapper.setResultType(resultType);
                //把key和value存入mappers中
                mappers.put(key,mapper);
            }
            return mappers;
        }catch(Exception e){
            throw new RuntimeException(e);
        }finally{
            in.close();
        }
    }

    /**
     * 根据传入的参数，得到dao中所有被select注解标注的方法。
     * 根据方法名称和类名，以及方法上注解value属性的值，组成Mapper的必要信息
     * @param daoClassPath
     * @return
     */
    private static Map<String,Mapper> loadMapperAnnotation(String daoClassPath)throws Exception{
        //定义返回值对象
        Map<String,Mapper> mappers = new HashMap<String, Mapper>();

        //1.得到dao接口的字节码对象
        Class daoClass = Class.forName(daoClassPath);
        //2.得到dao接口中的方法数组
        Method[] methods = daoClass.getMethods();
        //3.遍历Method数组
        for(Method method : methods){
            //取出每一个方法，判断是否有select注解
            boolean isAnnotated = method.isAnnotationPresent(Select.class);
            if(isAnnotated){
                //创建Mapper对象
                Mapper mapper = new Mapper();
                //取出注解的value属性值
                Select selectAnno = method.getAnnotation(Select.class);
                String queryString = selectAnno.value();
                mapper.setQueryString(queryString);
                //获取当前方法的返回值，还要求必须带有泛型信息
                Type type = method.getGenericReturnType();//List<User>
                //判断type是不是参数化的类型
                if(type instanceof ParameterizedType){
                    //强转
                    ParameterizedType ptype = (ParameterizedType)type;
                    //得到参数化类型中的实际类型参数
                    Type[] types = ptype.getActualTypeArguments();
                    //取出第一个
                    Class domainClass = (Class)types[0];
                    //获取domainClass的类名
                    String resultType = domainClass.getName();
                    //给Mapper赋值
                    mapper.setResultType(resultType);
                }
                //组装key的信息
                //获取方法的名称
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();
                String key = className+"."+methodName;
                //给map赋值
                mappers.put(key,mapper);
            }
        }
        return mappers;
    }

}
 

----------------------log4j.properties---------------------

# Set root category priority to INFO and its only appender to CONSOLE.
#log4j.rootCategory=INFO, CONSOLE            debug   info   warn error fatal
log4j.rootCategory=debug, CONSOLE, LOGFILE

# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE

# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n

# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=d:\axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n
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