diff --git a/README.MD b/README.MD
index c9c680b..6ce91a7 100644
--- a/README.MD
+++ b/README.MD
@@ -8,17 +8,32 @@
 
 ## 链接🖇
 
+### 课程实验🧪
+
 - ~~实验一 敬请期待~~
+
 - ~~实验二 敬请期待~~
+
 - [实验三](实验三.sql)
+
 - [实验四](实验四.sql)
+
 - [实验五](实验五.sql)
+
 - [实验六](实验六.sql)
+
 - [实验七](实验七.sql)
+
 - [实验八](实验八.sql)
+
 - [实验九](实验九.sql)
+
 - [实验十](实验十.sql)
 
+### 课后作业📖
+
+[课后作业](课后作业/)
+
 ## BB空间📺
 
 [B站](https://space.bilibili.com/521936200)
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diff --git a/课后作业/4.1.sql b/课后作业/4.1.sql
new file mode 100644
index 0000000..ffdd38e
--- /dev/null
+++ b/课后作业/4.1.sql
@@ -0,0 +1,35 @@
+CREATE DATABASE SPJ;
+
+USE SPJ;
+
+CREATE TABLE S(
+SNO VARCHAR(8),
+SNAME VARCHAR(32),
+STATUS SMALLINT,
+CITY VARCHAR(16),
+PRIMARY KEY(SNO)
+);
+
+CREATE TABLE P(
+PNO VARCHAR(8),
+PNAME VARCHAR(32),
+COLOR VARCHAR(8),
+WEIGHT DECIMAL,
+PRIMARY KEY(PNO)
+);
+
+CREATE TABLE J(
+JNO VARCHAR(8) PRIMARY KEY,
+JNAME VARCHAR(32),
+CITY VARCHAR(16)
+);
+
+CREATE TABLE SPJ(
+SNO VARCHAR(8),
+PNO VARCHAR(8),
+JNO VARCHAR(8),
+QTY SMALLINT,
+FOREIGN KEY (SNO) REFERENCES S(SNO),
+FOREIGN KEY (PNO) REFERENCES P(PNO),
+FOREIGN KEY (JNO) REFERENCES J(JNO)
+);
\ No newline at end of file
diff --git a/课后作业/4.2.sql b/课后作业/4.2.sql
new file mode 100644
index 0000000..f13c872
--- /dev/null
+++ b/课后作业/4.2.sql
@@ -0,0 +1,50 @@
+USE SPJ;
+
+INSERT INTO S(SNO,SNAME,STATUS,CITY)
+VALUES
+('S1','精益',20,'天津'),
+('S2','盛锡',10,'北京'),
+('S3','东方红',30,'北京'),
+('S4','丰泰盛',20,'天津'),
+('S5','为民',30,'上海');
+
+INSERT INTO P(PNO,PNAME,COLOR,WEIGHT)
+VALUES
+('P1','螺母','红',12),
+('P2','螺栓','绿',17),
+('P3','螺丝刀','蓝',14),
+('P4','螺丝刀','红',14),
+('P5','凸轮','蓝',40),
+('P6','齿轮','红',30);
+
+INSERT INTO J(JNO,JNAME,CITY)
+VALUES
+('J1','三建','北京'),
+('J2','一汽','长春'),
+('J3','弹簧厂','天津'),
+('J4','造船厂','天津'),
+('J5','机车厂','唐山'),
+('J6','无线电厂','常州'),
+('J7','半导体厂','南京');
+
+INSERT INTO SPJ (SNO, PNO, JNO, QTY)
+VALUES
+('S1', 'P1', 'J1', 200),
+('S1', 'P1', 'J3', 100),
+('S1', 'P1', 'J4', 700),
+('S1', 'P2', 'J2', 100),
+('S2', 'P3', 'J1', 400),
+('S2', 'P3', 'J2', 200),
+('S2', 'P3', 'J4', 500),
+('S2', 'P3', 'J5', 400),
+('S2', 'P5', 'J1', 400),
+('S2', 'P5', 'J2', 100),
+('S3', 'P1', 'J1', 200),
+('S3', 'P3', 'J1', 200),
+('S4', 'P5', 'J1', 100),
+('S4', 'P6', 'J3', 300),
+('S4', 'P6', 'J4', 200),
+('S5', 'P2', 'J4', 100),
+('S5', 'P3', 'J1', 200),
+('S5', 'P6', 'J2', 200),
+('S5', 'P6', 'J4', 500);
diff --git a/课后作业/4.3.sql b/课后作业/4.3.sql
new file mode 100644
index 0000000..1a90978
--- /dev/null
+++ b/课后作业/4.3.sql
@@ -0,0 +1,20 @@
+USE SPJ;
+
+-- ①
+SELECT SNO FROM SPJ WHERE JNO='J1';
+
+-- ②
+SELECT SNO FROM SPJ WHERE JNO='J1' AND PNO='P1';
+
+-- ③
+SELECT SPJ.SNO
+FROM SPJ
+JOIN P ON SPJ.PNO = P.PNO
+WHERE SPJ.JNO = 'J1' AND P.COLOR = '红';
+
+-- ④
+SELECT SPJ.JNO
+FROM SPJ
+JOIN S ON SPJ.SNO=S.SNO
+JOIN P ON SPJ.PNO=P.PNO
+WHERE P.COLOR!='红' AND S.CITY!='天津';
\ No newline at end of file
diff --git a/课后作业/5.sql b/课后作业/5.sql
new file mode 100644
index 0000000..70dacfa
--- /dev/null
+++ b/课后作业/5.sql
@@ -0,0 +1,56 @@
+USE SPJ;
+
+-- ①
+SELECT SNO,CITY FROM S;
+
+-- ②
+SELECT PNAME,COLOR,WEIGHT FROM P;
+
+-- ③
+SELECT JNO FROM SPJ WHERE SNO='S1';
+
+-- ④
+SELECT P.PNAME,SPJ.QTY
+FROM SPJ
+JOIN J ON SPJ.JNO=J.JNO
+JOIN P ON SPJ.PNO=P.PNO
+WHERE J.JNO='J2';
+
+-- ⑤
+SELECT SPJ.PNO
+FROM SPJ
+JOIN S ON SPJ.SNO=S.SNO
+WHERE S.CITY='上海';
+
+-- ⑥
+SELECT J.JNAME
+FROM SPJ
+JOIN J ON SPJ.JNO=J.JNO
+JOIN S ON SPJ.SNO=S.SNO
+WHERE S.CITY='上海';
+
+-- ⑦
+SELECT SPJ.JNO
+FROM SPJ
+JOIN S ON SPJ.SNO=S.SNO
+WHERE S.CITY != '天津';
+
+-- ⑧
+UPDATE P
+SET COLOR='蓝'
+WHERE COLOR='红';
+
+-- ⑨
+UPDATE SPJ
+SET SNO='S3'
+WHERE SNO='S5' AND PNO='P6' AND JNO='J2';
+
+-- ⑩
+DELETE FROM SPJ
+WHERE SNO='S2';
+DELETE FROM S
+WHERE SNO='S2';
+
+-- ⑪
+INSERT INTO SPJ(SNO,JNO,PNO,QTY)
+VALUES('S2','J6','P4',200);
\ No newline at end of file