1 cse 480: database systems lecture 9: sql-ddl reference: read chapter 4.1-4.2 of the textbook

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CSE 480: Database Systems

Lecture 9: SQL-DDL

Reference:

Read Chapter 4.1-4.2 of the textbook

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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

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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

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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

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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

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CREATE TABLE

struct DepartmentType{char Dname[10]; int Dnumber;}; DepartmentType DEPARTMENT; /* 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 keyMGRSTARTDATE 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

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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/)

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MySQL Data Type Examples

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MySQL Data Type Examples

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Attribute Constraints

Default values for attributes

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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)

);

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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;

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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

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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

xx

RR SS

Request to delete row in B

FKFK PKPK

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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

xx

RR SS

Request to modify PK in S

FKFK PKPK

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Exercise

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Exercise

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Exercise

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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;

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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);

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TRUNCATE TABLE

Remove all the rows in Employee table

TRUNCATE TABLE EMPLOYEE;

– Table will be empty after truncated

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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

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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;

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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;

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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

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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!

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Example

N 1Employee Department

Works_For

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Example

N 1Employee Department

Works_For

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Example

N 1Employee Department

Works_For

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Example

Foreign key is not enforced in this example

No dnumber = 3 in department table

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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)

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Example

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Example

Foreign key works now!!

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Example

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

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Example

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