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Leo branch #77

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647eb87
数据库实战: SELECT命令与JDBC使用
leo2c Feb 6, 2020
6efdfbb
提取重复代码为公共方法
leo2c Feb 7, 2020
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106 changes: 95 additions & 11 deletions src/main/java/com/github/hcsp/sql/Sql.java
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@

package com.github.hcsp.sql;

import java.io.File;
import java.math.BigDecimal;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class Sql {
Expand Down Expand Up @@ -72,8 +72,10 @@ public String toString() {
* 题目1：
* 查询有多少所有用户曾经买过指定的商品
*
* @param goodsId 指定的商品ID
* @param goodsId 指定的商品ID
* @param databaseConnection 数据库连接对象
* @return 有多少用户买过这个商品
* @throws SQLException SQL异常
*/
// 例如，输入goodsId = 1，返回2，因为有2个用户曾经买过商品1。
// +-----+
Expand All @@ -82,16 +84,26 @@ public String toString() {
// | 2 |
// +-----+
public static int countUsersWhoHaveBoughtGoods(Connection databaseConnection, Integer goodsId) throws SQLException {
return 0;
try (PreparedStatement statement = databaseConnection.prepareStatement("select count(distinct USER_ID) from \"ORDER\" where GOODS_ID = ?")) {
statement.setInt(1, goodsId);
statement.executeQuery();
ResultSet resultSet = statement.getResultSet();
while (resultSet.next()) {
return resultSet.getInt(1);
}
}
return -1;
}

/**
* 题目2：
* 分页查询所有用户，按照ID倒序排列
*
* @param pageNum 第几页，从1开始
* @param pageSize 每页有多少个元素
* @param pageNum 第几页，从1开始
* @param pageSize 每页有多少个元素
* @param databaseConnection 数据库连接对象
* @return 指定页中的用户
* @throws SQLException SQL异常
*/
// 例如，pageNum = 2, pageSize = 3（每页3个元素，取第二页），则应该返回：
// +----+----------+------+----------+
Expand All @@ -100,7 +112,22 @@ public static int countUsersWhoHaveBoughtGoods(Connection databaseConnection, In
// | 1 | zhangsan | tel1 | beijing |
// +----+----------+------+----------+
public static List<User> getUsersByPageOrderedByIdDesc(Connection databaseConnection, int pageNum, int pageSize) throws SQLException {
return null;
List<User> userList = new ArrayList<>();
try (PreparedStatement statement = databaseConnection.prepareStatement("select * from user order by id desc limit ?,?")) {
statement.setInt(1, (pageNum - 1) * pageSize);
statement.setInt(2, pageSize);
statement.executeQuery();
ResultSet resultSet = statement.getResultSet();
while (resultSet.next()) {
User user = new User();
user.id = resultSet.getInt(1);
user.name = resultSet.getString(2);
user.tel = resultSet.getString(3);
user.address = resultSet.getString(4);
userList.add(user);
}
}
return userList;
}

// 商品及其营收
Expand All @@ -118,6 +145,10 @@ public String toString() {
/**
* 题目3：
* 查询所有的商品及其销售额，按照销售额从大到小排序
*
* @param databaseConnection 数据库连接对象
* @return 商品id, 商品名称, 商品销售总额列表
* @throws SQLException SQL异常
*/
// 预期的结果应该如图所示
// +----+--------+------+
Expand All @@ -132,7 +163,22 @@ public String toString() {
// | 3 | goods3 | 20 |
// +----+--------+------+
public static List<GoodsAndGmv> getGoodsAndGmv(Connection databaseConnection) throws SQLException {
return null;
List<GoodsAndGmv> goodsAndGmvList = new ArrayList<>();
try (PreparedStatement statement = databaseConnection.prepareStatement("select \"GOODS\".id,GOODS.name, sum(\"ORDER\".GOODS_NUM*\"ORDER\".GOODS_PRICE) as gmv from \"ORDER\"\n" +
"join GOODS on \"ORDER\".GOODS_ID = GOODS.ID\n" +
"group by \"GOODS\".ID\n" +
"order by gmv desc")) {
statement.executeQuery();
ResultSet resultSet = statement.getResultSet();
while (resultSet.next()) {
GoodsAndGmv goodsAndGmv = new GoodsAndGmv();
goodsAndGmv.goodsId = resultSet.getInt(1);
goodsAndGmv.goodsName = resultSet.getString(2);
goodsAndGmv.gmv = resultSet.getBigDecimal(3);
goodsAndGmvList.add(goodsAndGmv);
}
}
return goodsAndGmvList;
}


Expand All @@ -152,6 +198,10 @@ public String toString() {
/**
* 题目4：
* 查询订单信息，只查询用户名、商品名齐全的订单，即INNER JOIN方式
*
* @param databaseConnection 数据库连接对象
* @return 订单信息
* @throws SQLException SQL异常
*/
// 预期的结果为：
// +----------+-----------+------------+-------------+
Expand All @@ -170,12 +220,25 @@ public String toString() {
// | 6 | zhangsan | goods3 | 20 |
// +----------+-----------+------------+-------------+
public static List<Order> getInnerJoinOrders(Connection databaseConnection) throws SQLException {
return null;
List<Order> orderList = new ArrayList<>();
try (PreparedStatement statement = databaseConnection.prepareStatement("select \"ORDER\".id, USER.NAME, GOODS.NAME,\"ORDER\".GOODS_NUM*\"ORDER\".GOODS_PRICE as TOTAL_PRICE\n" +
"from \"ORDER\"\n" +
" join GOODS on \"ORDER\".GOODS_ID = GOODS.ID\n" +
" join USER on \"ORDER\".USER_ID = USER.ID")) {
statement.executeQuery();
ResultSet resultSet = statement.getResultSet();
conversionResultSetToOrderList(resultSet, orderList);
}
return orderList;
}

/**
* 题目5：
* 查询所有订单信息，哪怕它的用户名、商品名缺失，即LEFT JOIN方式
*
* @param databaseConnection 数据库连接对象
* @return 订单信息
* @throws SQLException SQL异常
*/
// 预期的结果为：
// +----------+-----------+------------+-------------+
Expand All @@ -198,9 +261,30 @@ public static List<Order> getInnerJoinOrders(Connection databaseConnection) thro
// | 8 | NULL | NULL | 60 |
// +----------+-----------+------------+-------------+
public static List<Order> getLeftJoinOrders(Connection databaseConnection) throws SQLException {
return null;
List<Order> orderList = new ArrayList<>();
try (PreparedStatement statement = databaseConnection.prepareStatement("select \"ORDER\".id, USER.NAME, GOODS.NAME, \"ORDER\".GOODS_NUM * \"ORDER\".GOODS_PRICE as TOTAL_PRICE\n" +
"from \"ORDER\"\n" +
" left join GOODS on \"ORDER\".GOODS_ID = GOODS.ID\n" +
" left join USER on \"ORDER\".USER_ID = USER.ID")) {
statement.executeQuery();
ResultSet resultSet = statement.getResultSet();
conversionResultSetToOrderList(resultSet, orderList);
}
return orderList;
}

private static void conversionResultSetToOrderList(ResultSet resultSet, List<Order> orderList) throws SQLException {
while (resultSet.next()) {
Order order = new Order();
order.id = resultSet.getInt(1);
order.userName = resultSet.getString(2);
order.goodsName = resultSet.getString(3);
order.totalPrice = resultSet.getBigDecimal(4);
orderList.add(order);
}
}


// 注意，运行这个方法之前，请先运行mvn initialize把测试数据灌入数据库
public static void main(String[] args) throws SQLException {
File projectDir = new File(System.getProperty("basedir", System.getProperty("user.dir")));
Expand Down