IMS1907 Database Systems Summer Semester 2004/2005 Lecture 9 Structured Query Language – SQL Data...

IMS1907 Database Systems

Summer Semester 2004/2005

Lecture 9

Structured Query Language – SQLData Definition Language - DDL

Monash University 2004 2

Has become de facto language for creating and querying relational databases– mainframe and personal database environments

Accepted as a standard– ANSI, FIPS, ISO

First published in 1986– updated in 1989, 1992 (SQL-92), 1999 (SQL-99)

and 2003 (SQL:2003)

Structured Query Language - SQL


SQL-99 was a significant extension on SQL-92– added regular expression matching, recursive

queries, triggers, non-scalar types and some object-oriented features (the last two are somewhat controversial and not yet widely supported)

SQL:2003– introduced XML-related features, standardized

sequences and columns with auto-generated values (including identity-columns)



Benefits of a standard relational language– reduced training costs– increased productivity– increased application portability– extended application longevity– reduced dependence on single vendor– enhanced cross-system communication



Disadvantages of a standard relational language– stifle creativity and innovation

• standardisation – the natural enemy of variety– may not meet all user needs– not ideal as a result of being a set of compromises

between many industry parties– difficult to change– vendor features can limit portability and offset

other advantages



Concepts– catalog– schema– data definition language (DDL)– data manipulation language (DML)– data control language (DCL)

The SQL Environment


Catalog– a set of schemas which, when put together,

constitute a description of a database– describes any object that is part of a database– a DBMS may manage many catalogs

Schema– a structure containing descriptions of objects

created by users• base tables, views, domains, constraints,

character sets, triggers, roles, …

The SQL Environment


Data definition language (DDL)– commands used to define a database– used to create, change and remove objects from a

database and establish constraints– generally restricted to one or more DBAs to

protect database from unexpected changes– DDL statements include

• CREATE, ALTER, DROP• In MySQL we also need the USE statement

The SQL Environment


Data manipulation language (DML)– considered by many as the core SQL commands– commands used to maintain and query a database– used to update, insert, change and query data– can be interactive or embedded in programs

• embedded SQL gives programmer more control over report timing, interface appearance, error handling and database security

– some common DML statements include• INSERT, DELETE, SELECT, SHOW, DESCRIBE

The SQL Environment


DML allows us to perform the following relational operations– select

• selects a subset of rows in a table satisfying a selection criteria

– project• selects only certain columns from a table

– join• combines data from two or more tables based on

one or more common values

The SQL Environment


Data control language (DCL)– commands used to control a database– used to administer privileges and the committing of

data– controls granting and revoking of access, and retrieving

and storing transactions that could affect database– generally restricted to DBAs to protect database from

unexpected changes and unauthorised access– DCL statements include

• GRANT, REVOKE, LOAD, BACKUP, ROLLBACK

The SQL Environment


Each DBMS has a defined list of data types it can handleAll have equivalents for structured data types– numeric, string and date/time variables

Many allow for unstructured data types– graphic, image, spatial

When creating a table, the data type for each attribute must be specifiedChoice of data type depends on – data values that need to be stored– expected uses of data

The SQL Environment – Data Types


MySQL DatatypesMySQL Length Oracle VB6

TINYINT -128 to 127 characters

NUMBER

integer

TINYINT UNSIGNED 0 to 255 characters byte

SMALLINT -32,768 to 32,767 characters

integer

SMALLINT UNSIGNED 0 to 65, 535 characters

long

MEDIUMINT -8,388,608 to 8,388,607 characters

MEDIUMINT UNSIGNED 0 to 16,777,215 characters

INT -2,147,483,647 to 2,147,483,647 characters

INT UNSIGNED 0 to 4,294,967,295 characters

double

BIGINT 64 Bit N/A


MySQL Datatypes

MySQL Length Oracle VB6

FLOAT 32 bit floating pointNUMBER

single

DOUBLE 64 bit floating pointdouble

DECIMAL variable floating point

CHAR 1 to 255 characters - fixed CHAR

string

VARCHAR 1 to 255 characters - variable

VARCHAR2TINYTEXT 1 to 255 characters -

variable

TEXT 1 to 65,535 characters

LONGMEDIUMTEXT 1 to 16,777,215

characters

LONGTEXT 1 to 4,294,967,295 characters

N/A


MySQL Datatypes

MySQL Length Oracle VB6

all BLOB types 1 to 4,294,967,295 bytes

LOB Variant

DATE Date without time

DATEDate and time value

DATETIME Date and time

TIMESTAMP Date and time

TIME Time

YEAR Year integer

ENUM Enumeration of value set

ENUMstring

SET Set of values


Three DDL CREATE commands are included in SQL-92 and later versions of standard– CREATE DATABASE (or CREATE SCHEMA in Oracle)

• used to define portion of database owned by user• contains tables, views, domains, constraints, …

– CREATE TABLE• defines table and its columns• dependent on a schema

– CREATE VIEW• defines logical table from one or more tables or

views

Data Definition Language (DDL)


Other DDL CREATE commands are also included in SQL-92 and later versions of standard– CREATE CHARACTER SET– CREATE COLLATION– CREATE TRANSLATION– CREATE ASSERTION– CREATE DOMAIN

Other statements such as CREATE INDEX are performance-related and not part of standard



The DROP command is used to reverse CREATE commands– DROP DATABASE (or DROP SCHEMA in Oracle)

• removes entire database and related schemas– DROP TABLE

• removes table and related columns and constraints from database

– DROP VIEW• removes logical table from database schema

Other DROP commands can remove keys, indexes, users, ..



The ALTER command is used to change objects created using the CREATE command– ALTER DATABASE (or ALTER SCHEMA in Oracle)

• changes DB characteristics – character sets, collations

– ALTER TABLE, ALTER COLUMN• changes table definitions by altering column

specifications– ALTER VIEW

• changes specifications of logical tableCan include ALTER, ADD, DROP keywords



At the mysql> prompt enter the command and the name of the database you want to create– mysql> CREATE DATABASE menagerie;

Creating a database in MySQL does not automatically select it for useSelect a database for use with the use command and the name of the database you want to use– mysql> USE menagerie;

Creating a Database


Once a database has been selected you can create tablesCreating tables requires that you define– column names– data types and lengths– column and table keys and constraints

Although MySQL does not necessarily require you to specify keys and constraints, they should be defined if known

Creating Tables


Use the CREATE TABLE statement to define the layout of the tableCREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20), species

VARCHAR(20), sex CHAR(1), birth DATE, death DATE);

You can specify more detail about your table by defining keys and constraints

Creating Tables


CREATE TABLE person (person_id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT, name VARCHAR(60) NOT NULL, PRIMARY KEY (person_id)); CREATE TABLE shirt (shirt_id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT, style ENUM('t-shirt', 'polo', 'dress') NOT NULL, color ENUM('red', 'blue', 'orange', 'white', 'black') NOT NULL, owner SMALLINT UNSIGNED NOT NULL REFERENCES person(person_id), PRIMARY KEY (shirt_id));

Creating Tables


Use the ALTER TABLE statement to re-define the layout of the table– add/remove/rename columns, constraints, keys,

types, … ALTER TABLE person ADD (address VARCHAR(60) NOT NULL); ALTER TABLE person MODIFY (name VARCHAR(40) NOT NULL);

Altering Tables


Use the DROP DATABASE command to remove a database and all related tables and schemasEnter the command and the name of the databaseDROP DATABASE menagerie; You can add the optional keywords IF EXISTS to prevent errors occurring for non-existent databases DROP DATABASE IF EXISTS menagerie; Use this command with caution!

Deleting a Database


Use the DROP TABLE command to remove a table and all its related definitionsEnter the command and the name of the table DROP TABLE pet; You can add the optional keywords IF EXISTS to prevent errors occurring for non-existent tables DROP TABLE IF EXISTS pet; You can use this command to remove one or more tables

Deleting a Table


References

Bordoloi, B. and Bock, D., (2004), Oracle SQL, Pearson Education Inc., Upper Saddle River, NJ, USA.

Hillyer, M., (2004), Visual Basic / MySQL Datatypes, last accessed 10th September 2004 at http://dev.mysql.com/tech-resources/articles/visual-basic-datatypes.html

Hoffer, J.A., Prescott, M.B. and McFadden, F.R., (2005), Modern Database Management, (7th edn.), Pearson Education Inc., Upper Saddle River, NJ, USA.


References

Kroenke, D.M., (2004), Database Processing: Fundamentals, Design and Implementation, (9th edn.), Pearson Education Inc., Upper Saddle River, NJ, USA.

MySQL Reference Manual, (2004), last accessed 10th September 2004 at http://dev.mysql.com/doc/mysql/

IMS1907 Database Systems Summer Semester 2004/2005 Lecture 9 Structured Query Language – SQL Data...

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