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Merged
hcsp-bot merged 4 commits into from
Nov 20, 2021
Merged

Dingzheng #191

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084db95
SELECT命令与JDBC使用
zdmhahaha Nov 19, 2021
f2de814
geshihua
zdmhahaha Nov 19, 2021
e974b22
dingzheng
zdmhahaha Nov 19, 2021
8d16528
去掉注释
zdmhahaha Nov 20, 2021
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112 changes: 72 additions & 40 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.*;

@hcsp-bot hcsp-bot Nov 20, 2021

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不应使用 '.*' 形式的导入 - java.sql.* 。

import java.util.ArrayList;
import java.util.List;

public class Sql {
Expand Down Expand Up @@ -68,39 +68,47 @@ 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
* @return 有多少用户买过这个商品
*/
// 例如，输入goodsId = 1，返回2，因为有2个用户曾经买过商品1。

// +-----+
// |count|
// +-----+
// | 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);
ResultSet resultSet = statement.executeQuery();
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
* @return 指定页中的用户
*/
// 例如，pageNum = 2, pageSize = 3（每页3个元素，取第二页），则应该返回：

// +----+----------+------+----------+
// | ID | NAME | TEL | ADDRESS |
// +----+----------+------+----------+
// | 1 | zhangsan | tel1 | beijing |
// +----+----------+------+----------+
public static List<User> getUsersByPageOrderedByIdDesc(Connection databaseConnection, int pageNum, int pageSize) throws SQLException {
return null;
try (PreparedStatement statement = databaseConnection.prepareStatement("select id, name, tel ,address from `user` ORDER BY ID DESC limit ?,?")) {
statement.setInt(1, pageSize * (pageNum - 1));
statement.setInt(2, pageSize);
ResultSet resultSet = statement.executeQuery();

List<User> list = new ArrayList<>();
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);
list.add(user);
}
return list;
}
}

// 商品及其营收
Expand All @@ -115,11 +123,7 @@ 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
*/
// 预期的结果应该如图所示

// +----+--------+------+
// | ID | NAME | GMV |
// +----+--------+------+
Expand All @@ -132,7 +136,19 @@ public String toString() {
// | 3 | goods3 | 20 |
// +----+--------+------+
public static List<GoodsAndGmv> getGoodsAndGmv(Connection databaseConnection) throws SQLException {
return null;
try (PreparedStatement statement = databaseConnection.prepareStatement("select goods_id ,name,sum(goods_num * goods_price) as GMV from `order` join goods on `order`.goods_id = goods.id group by goods_id order by GMV desc")) {

ResultSet resultSet = statement.executeQuery();
List<GoodsAndGmv> list = new ArrayList<>();
while (resultSet.next()) {
GoodsAndGmv goodsAndGmv = new GoodsAndGmv();
goodsAndGmv.goodsId = resultSet.getInt(1);
goodsAndGmv.goodsName = resultSet.getString(2);
goodsAndGmv.gmv = resultSet.getBigDecimal(3);
list.add(goodsAndGmv);
}
return list;
}
}


Expand All @@ -149,11 +165,7 @@ 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
*/
// 预期的结果为：

// +----------+-----------+------------+-------------+
// | ORDER_ID | USER_NAME | GOODS_NAME | TOTAL_PRICE |
// +----------+-----------+------------+-------------+
Expand All @@ -170,14 +182,22 @@ public String toString() {
// | 6 | zhangsan | goods3 | 20 |
// +----------+-----------+------------+-------------+
public static List<Order> getInnerJoinOrders(Connection databaseConnection) throws SQLException {
return null;
try (PreparedStatement statement = databaseConnection.prepareStatement("select `order`.id, user.name, goods.name,goods_price*goods_num as total from `order` join user on `order`.user_id = user.id join goods on `order`.goods_id = goods.id")) {

ResultSet resultSet = statement.executeQuery();
List<Order> list = new ArrayList<>();
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);
list.add(order);
}
return list;
}
}

/**
* 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
*/
// 预期的结果为：
// +----------+-----------+------------+-------------+
// | ORDER_ID | USER_NAME | GOODS_NAME | TOTAL_PRICE |
// +----------+-----------+------------+-------------+
Expand All @@ -198,7 +218,19 @@ public static List<Order> getInnerJoinOrders(Connection databaseConnection) thro
// | 8 | NULL | NULL | 60 |
// +----------+-----------+------------+-------------+
public static List<Order> getLeftJoinOrders(Connection databaseConnection) throws SQLException {
return null;
try (PreparedStatement statement = databaseConnection.prepareStatement("select `order`.id, user.name, goods.name,goods_price*goods_num as total from `order` left join user on `order`.user_id = user.id left join goods on `order`.goods_id = goods.id")) {
ResultSet resultSet = statement.executeQuery();
List<Order> list = new ArrayList<>();
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);
list.add(order);
}
return list;
}
}

// 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
Expand Down