Merge pull request #316 from NikhilBhargav/main

How to Alter Constraints in SQL

Author: milos-simic

sql-constraints/sql-alter-constraint/alter_constraint_mysql.sql

@@ -0,0 +1,30 @@
+INSERT INTO Department (id, name, code) VALUES
+  (6, 'Social Sciences and Humanities', 'SSH');
+
+
+-- Insert in Course for SSH
+INSERT INTO Course (id, name, textbook, credits, is_active, department_id) VALUES
+  ('SSH111', 'Macroeconomics', 'Macroeconomics by Krugman, P., Wells, R., 2nd edition', 4, 'Yes', 6),
+  ('SSH211', 'Econometrics I', 'Introductory Econometrics: A modern approach by Jeffrey M. Wooldridge (4th edition, Cengage India)', 4, 'Yes', 6),
+  ('SSH411', 'Econometrics II', 'Microeconometrics: Methods and Applications by A. Colin Cameron and Pravin K. Trivedi', 6, 'Yes', 6),
+  ('SSH112', 'Market Design', 'Auction Theory by Vijay Krishna, Academic Press', 4, 'Yes', 6);
+
+
+--Drop the constraint
+ALTER TABLE Course
+DROP CONSTRAINT course_department_id_fkey;
+
+--Recreate
+ALTER TABLE Course
+ADD CONSTRAINT course_department_id_fkey
+FOREIGN KEY (department_id) REFERENCES Department(id)
+ON DELETE CASCADE;
+
+DELETE 
+FROM Department 
+WHERE id=6;
+
+ALTER TABLE Student
+ADD CONSTRAINT CHK_GPA 
+CHECK (gpa BETWEEN 3.0 AND 5.0);
+

sql-constraints/sql-alter-constraint/alter_constraint_postgres.sql

@@ -0,0 +1,29 @@
+INSERT INTO Department (id, name, code) VALUES
+  (6, 'Social Sciences and Humanities', 'SSH');
+
+-- Insert in Course for SSH
+INSERT INTO Course (id, name, textbook, credits, is_active, department_id) VALUES
+  ('SSH111', 'Macroeconomics', 'Macroeconomics by Krugman, P., Wells, R., 2nd edition', 4, 'Yes', 6),
+  ('SSH211', 'Econometrics I', 'Introductory Econometrics: A modern approach by Jeffrey M. Wooldridge (4th edition, Cengage India)', 4, 'Yes', 6),
+  ('SSH411', 'Econometrics II', 'Microeconometrics: Methods and Applications by A. Colin Cameron and Pravin K. Trivedi', 6, 'Yes', 6),
+  ('SSH112', 'Market Design', 'Auction Theory by Vijay Krishna, Academic Press', 4, 'Yes', 6);
+
+--Drop the constraint
+ALTER TABLE Course
+DROP CONSTRAINT course_department_id_fkey;
+
+--Recreate
+ALTER TABLE Course
+ADD CONSTRAINT course_department_id_fkey
+FOREIGN KEY (department_id) REFERENCES Department(id)
+ON DELETE CASCADE;
+
+--Delete Course
+DELETE 
+FROM Department 
+WHERE id=6;
+
+ALTER TABLE Student
+ADD CONSTRAINT CHK_GPA 
+CHECK (gpa BETWEEN 3.0 AND 5.0);
+

sql-constraints/sql-alter-constraint/alter_constraint_sqlserver2022.sql

@@ -0,0 +1,33 @@
+INSERT INTO Department (id, name, code) VALUES
+  (6, 'Social Sciences and Humanities', 'SSH');
+
+--Insert in Course for SSH
+INSERT INTO Course (id, name, textbook, credits, is_active, department_id) VALUES
+  ('SSH111', 'Macroeconomics', 'Macroeconomics by Krugman, P., Wells, R., 2nd edition', 4, 'Yes', 6),
+  ('SSH211', 'Econometrics I', 'Introductory Econometrics: A modern approach by Jeffrey M. Wooldridge (4th edition, Cengage India)', 4, 'Yes', 6),
+  ('SSH411', 'Econometrics II', 'Microeconometrics: Methods and Applications by A. Colin Cameron and Pravin K. Trivedi', 6, 'Yes', 6),
+  ('SSH112', 'Market Design', 'Auction Theory by Vijay Krishna, Academic Press', 4, 'Yes', 6);
+
+--List constraints
+SELECT CONSTRAINT_NAME, CONSTRAINT_TYPE 
+FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS 
+WHERE TABLE_NAME = 'Course';
+
+--Drop and alter constraint in same query 
+ALTER TABLE Course 
+NO CHECK CONSTRAINT course_department_id_fkey, 
+DROP CONSTRAINT course_department_id_fkey, 
+ADD CONSTRAINT course_department_id_fkey 
+FOREIGN KEY (department_id) REFERENCES Department(id) 
+ON DELETE CASCADE;
+
+--Delete the course SSH
+DELETE 
+FROM Department 
+WHERE id=6;
+
+
+ALTER TABLE Student
+ADD CONSTRAINT CHK_GPA 
+CHECK (gpa BETWEEN 3.0 AND 5.0);
+