day02

.gitignore

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+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store

pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.bwie</groupId>
+    <artifactId>day02</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <properties>
+        <maven.compiler.source>17</maven.compiler.source>
+        <maven.compiler.target>17</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+</project>

sql/day02.sql

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+create table t_student(
+	s_id int PRIMARY KEY auto_increment,
+	s_name VARCHAR(30) ,
+	sex VARCHAR(2)
+);
+
+create table t_course(
+	c_id int PRIMARY KEY auto_increment,
+	c_name VARCHAR(30) 
+);
+
+create table stu_cou(
+	sc_id int PRIMARY KEY auto_increment,
+	c_id int,
+	s_id int
+);
+
+INSERT INTO t_student(s_name,sex)VALUES
+('张三','男'), ('李四','男'), ('王五','男'), ('赵柳','女'),
+('田七','男'), ('王霸','男'), ('南丰','男'), ('梅梅','女'),
+('小气','女'), ('诺手','女'), ('阿萨德','男'), ('阿斯顿','男');
+
+INSERT into t_course(c_name) VALUES
+('语文'),('计算机'),('英语'),('数学');
+
+
+INSERT into stu_cou(s_id,c_id) VALUES
+(1,1),(1,3),(1,2),(2,1),(2,2),(2,4),(3,2),(3,1),(3,3),(4,1),
+(4,2),(4,4),(5,1),(5,2),(6,1),(6,3),(7,3),(7,2),(8,1),(9,2),
+(10,4),(9,1),(10,2),(11,4),(12,1),(12,3);
+
+
+#男女生各多少
+SELECT
+	sex,
+	COUNT(*) 
+FROM
+	t_student 
+GROUP BY
+	sex;
+
+
+
+#男女生分别占总人数的比例
+SELECT
+	sex,
+	CONCAT( ROUND( COUNT(*) / ( SELECT COUNT(*) FROM t_student )* 100, 2 ), '%' ) 
+FROM
+	t_student 
+GROUP BY
+	sex;
+
+
+#没门课程下的学生人数
+SELECT
+	c.c_name,
+	count(*) 
+FROM
+	t_course c
+	LEFT JOIN stu_cou sc ON sc.c_id = c.c_id
+	LEFT JOIN t_student s ON sc.s_id = s.s_id 
+GROUP BY
+	c_name
+
+

src/main/java/com/bwie/Main.java

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+package com.bwie;
+
+public class Main {
+    public static void main(String[] args) {
+        System.out.println("Hello world!");
+    }
+}