Merge pull request #4239 from szarnyasg/fk-constraints

Update FK example

docs/sql/constraints.md

@@ -97,10 +97,17 @@ Foreign keys define a column, or set of columns, that refer to a primary key or
 
 ```sql
 CREATE TABLE students (id INTEGER PRIMARY KEY, name VARCHAR);
-CREATE TABLE exams (student_id INTEGER REFERENCES students(id), grade INTEGER);
+CREATE TABLE subjects (id INTEGER PRIMARY KEY, name VARCHAR);
+CREATE TABLE exams (
+    exam_id INTEGER PRIMARY KEY,
+    subject_id INTEGER REFERENCES subjects(id),
+    student_id INTEGER REFERENCES students(id),
+    grade INTEGER
+);
 INSERT INTO students VALUES (1, 'Student 1');
-INSERT INTO exams VALUES (1, 10);
-INSERT INTO exams VALUES (2, 10);
+INSERT INTO subjects VALUES (1, 'CS 101');
+INSERT INTO exams VALUES (1, 1, 1, 10);
+INSERT INTO exams VALUES (2, 1, 2, 10);
 ```
 
 ```console