CSE 480: Database Systems

1. CSE 480: Database Systems • Lecture 9: SQL-DDL • Reference: • Read Chapter 4.1-4.2 of the textbook

2. Announcements • Exam 1 to be held on February 19 • Cover materials from lecture 1 – 7 (homework 1 and 2) • Open book and notes but no computer, cell phone, or other electronic devices

3. SQL • Stands for Structured Query Language • Has both DDL and DML components • Also contains additional facilities for • Defining views on the database • Specifying security and authorization • Specifying transaction controls • History • SEQUEL for IBM System R => SQL1 (1986) => SQL 1989 (minor variation) => SQL2 (1992) => SQL3 (1999) => SQL 2003, SQL 2006, and SQL 2008

4. SQL • Does not fully subscribe to all concepts in relational model • A relation is a set whereas a table is a bag (or multi-set) • An element may appear more than once in a bag • Every relation must have a primary key; yet SQL allows some tables not to have any key attributes

5. SQL DDL • Used to CREATE, DROP, and ALTER the descriptions of the tables (relation schema) in a database • Examples: • CREATE DATABASE(not needed unless you’re the system administrator) • CREATE TABLE • DROP TABLE • ALTER TABLE

6. CREATE TABLE struct DepartmentType{char Dname[10]; int Dnumber;}; DepartmentTypeDEPARTMENT; /* In C++ or C */ CREATE TABLE DEPARTMENT ( DNAME VARCHAR(10) NOT NULL, DNUMBER NUMBER(5) PRIMARY KEY, MGRSSN CHAR(9), MGRSTARTDATE CHAR(9) ); CREATE TABLE DEPT ( DNAME VARCHAR(10) NOT NULL, DNUMBER NUMBER(5) NOT NULL, MGRSSN CHAR(9), Secondary key MGRSTARTDATE CHAR(9), PRIMARY KEY (DNUMBER), UNIQUE (DNAME), FOREIGN KEY (MGRSSN) REFERENCES EMPLOYEE(SSN) ); NOTE: In MySQL, FOREIGN KEY is implemented in a slightly different way

7. MySQL Data Types • Numeric (int, float, real, double, decimal, smallint) • Character strings (char(n), varchar(m)) • Bit string (binary, varbinary) • Boolean • Date, time, and timestamp • Others (blobs, enum, text, geometric objects, etc) • To check the data types available for your Mysql: mysql> help data types or read documentation (http://dev.mysql.com/doc/)

8. MySQL Data Type Examples

9. MySQL Data Type Examples

10. Attribute Constraints • Default values for attributes

11. Attribute Constraints • CHECK clause (available in Oracle but not in MySQL) CREATE TABLE Department ( DName VARCHAR(15) NOT NULL, DNum INT NOT NULL, CHECK (DNum > 0 AND DNum < 21) );

12. CREATE TABLE By Copying • You can also create a table by copying the content from another table • Example: CREATE TABLE empl AS SELECT * FROM Employee;

13. REFERENTIAL INTEGRITY OPTIONS • We can specify RESTRICT, CASCADE, SET NULL or SET DEFAULT on referential integrity constraints (foreign keys) CREATE TABLE DEPT ( DNAME VARCHAR(10) NOT NULL, DNUMBER INTEGER NOT NULL, MGRSSN CHAR(9) DEFAULT '888665555', MGRSTARTDATE CHAR(9), PRIMARY KEY (DNUMBER), UNIQUE (DNAME), FOREIGN KEY (MGRSSN) REFERENCES EMPLOYEE(SSN) ON DELETE SET DEFAULT ON UPDATE CASCADE ); Specifies the corrective action upon constraint violation

14. Example for DELETE FOREIGN KEY (FK) REFERENCES S(PK) ON DELETE [ACTION] Possible choices of [ACTION]: • NO ACTION: Reject if row in R references row to be deleted (default option) • SET NULL: Set value of foreign key in A to NULL • SET DEFAULT: Set value of foreign key in A to default value which must exist in B • CASCADE: Delete referencing row(s) in A as well FK PK S R x x Request to delete row in B

15. Example for UPDATE FOREIGN KEY (FK) REFERENCES S(PK) ON UPDATE [ACTION] Possible choices of [ACTION]: • NO ACTION: Reject if row(s) in A references row to be updated (default response) • SET NULL: Set value of foreign key to null • SET DEFAULT: Set value of foreign key to default • CASCADE: Propagate new value to foreign key FK PK S R x x Request to modify PK in S

16. Exercise

17. Exercise

18. Exercise

19. DROP TABLE • Remove a relation and its definition • The relation can no longer be used in queries, updates, or any other commands since its description no longer exists • Example:DROP TABLE DEPENDENT;

20. ALTER TABLE • Add a new column to an existing table: ALTER TABLE EMPLOYEE ADD Jobtitle VARCHAR(12); • Remove a column from an existing table: ALTER TABLE EMPLOYEE DROP COLUMN Address; • Modify an existing column in a table: ALTER TABLE DEPARTMENT MODIFY Mgr_ssn CHAR(9) DEFAULT ‘333444555’; • Modify constraints of a table: ALTER TABLE DEPARTMENT DROP PRIMARY KEY; ALTER TABLE DEPARTMENT ADD PRIMARY KEY(DNUMBER);

21. TRUNCATE TABLE • Remove all the rows in Employee table TRUNCATE TABLE EMPLOYEE; • Table will be empty after truncated

22. MySQL • Mysql server is available on mysql-user.cse.msu.edu • You can log on to the server from any machine that has the mysql command line interpreter installed (e.g., arctic.cse.msu.edu) • Username is your MSU NetID • Password is your PID

23. Summary of useful MySQL commands • set password=password(‘new password’); • show databases; -- show the list of databases available to you • use dbname; -- use the database called dbname • show tables; -- show tables available • create table student ( id integer not null, name varchar(50) ); • describe student; • insert into student values (30, ‘john doe’); • select * from student; • truncate table student; • drop table student; • source script-file; -- executing SQL commands from a script-file • load data infile /path/file.txt into table skr;

24. MySQL Storage Engines • A storage engine is a low level data storage/retrieval module • MySQL supported multiple storage engines • MyISAM, InnoDB, Heap (Memory), BDB, Merge, … • You can specify which storage engine to use: CREATE TABLE t (i INT) ENGINE = INNODB; CREATE TABLE t (i INT) TYPE = MEMORY;

25. MySQL Databases • MySQL storage engines include both those that handle transaction-safe tables and those that handle non-transaction-safe tables • “Transaction-safe” tables would record all the database update operations in a log file • So even if MySQL crashes, you can still get your data back • You can execute ROLLBACK to undo your updates • Provides better concurrency • Disadvantage: slower especially when there are many concurrent update operations • Advantages of non-transaction-safe tables • Much faster • Lower disk space requirements

26. MySQL Storage Engines • MyISAM (usually, the default storage engine) • manages non-transactional tables. • provides high-speed storage and retrieval • Provides fulltext searching capabilities • InnoDB • provides transaction-safe tables • provides support for row locking and FOREIGN KEY constraints Important: Foreign key is not enforced in MySQL unless you use InnoDB as your storage engine!

27. Department Employee N 1 Works_For Example

28. Department Employee N 1 Works_For Example

29. Department Employee N 1 Works_For Example

30. Example Foreign key is not enforced in this example No dnumber = 3 in department table

31. Foreign key constraints in MySQL • In MySQL, foreign key constraints are supported by InnoDB storage engine only • Default storage engine in MySQL is MyISAM • So, you need to make sure the referenced and referencing relations are created using Innodb storage engine • You also need to create an index on the foreign key attributes: • Syntax: INDEX index_name(list_of_foreignkey_attributes) • Example: INDEX workson_fk_index1 (employeeID), INDEX workson_fk_index2 (projectID), FOREIGN KEY (employeeID) References Employee(ID), FOREIGN KEY (projectID) References Project(ID)

32. Example

33. Example Foreign key works now!!

34. Example Suppose we want to change ‘payroll’ dnumber from 1 to 3

35. Example Dnumber for John Doe automatically changes from 1 to 3 because foreign key constraint says “On update cascade”