Transcript Creating & Modifying Database tables

Creating Database Tables
1/21/2015
© Abdou Illia
MIS 4200 - Spring 2015
Objectives
Use structured query language (SQL) commands
to create, modify, and drop database tables
Explain Oracle 10g user schemas
Define Oracle 10g database tables
Create database tables using SQL*Plus
View information about your database tables using
Oracle 10g data dictionary views
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Introduction to SQL
Structured query language (SQL)
– Standard query language for relational databases
– Consists of about 30 commands
– Enables users to create database objects and
manipulate and view data
– SQL-99, SQL-2003, and SQL-2008
• Most recent versions
• Most vendors do not fully comply with SQL-2008
(but comply with SQL-92, SQL-99)
– Basic categories for SQL commands
• Data definition language (DDL)
• Data manipulation language (DML)
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Personal DBMS
With personal DBMS …
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You are usually the only user
You start the database application
You create a new database
The DBMS saves the database file in your
workstation’s file system
– You create database objects (tables, etc.)
Examples:
– MS Access
– Oracle Personal edition. But this DBMS derives
most of its features from the Oracle C/S version
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Oracle 10g Enterprise edition
A Client/server DBMS
User account
– Created for each user
– Identified using unique username and password
User schema
– Area of database belonging to user
Database objects
– Example: tables, forms, reports, …
– Also called schema objects
– Objects created by user reside in their user schema
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Defining Oracle Database Tables
 Tables
– Primary data objects in relational database
– When you create a new table, you must specify…
• Table name
• Each field data type/size
Each field (i.e. column) name
● You may specify constraints
●
 Constraints
– Restrictions on data values that column can store
 Oracle naming standard
– Rules established by Oracle corp. for naming objects
– One to 30 characters long
– Contain letters, numbers, and special symbols $, _, and #
– Begin with character
– Example: S_ID, f_id, PRICE, PRICE$, Not #ITEM.
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Defining Oracle Database Tables (cont.)
CREATE TABLE SQL syntax
CREATE TABLE tablename
(columnname1 data_type,
columnname2 data_type, …);
Example:
CREATE TABLE student
(s_id CHAR(5),
s_first VARCHAR2(20));
Basic data types
• Character
●
Number
●
Date/time
●
Large object
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Character Data Types
 VARCHAR2
– Variable-length character data (up to 4000 characters)
– Syntax: columnname VARCHAR2(maximum_size)
– If user enters data value less than maximum_size, DBMS
only stores actual character values
 CHAR
– Fixed-length character data (default = 2000)
– Syntax: columnname CHAR(maximum_size)
– If user enters data value less than maximum_size, DBMS
adds trailing blank spaces to the end of entry
 Oracle stores CHAR and VARCHAR2 data using the ASCII
coding
Q: s_last CHAR(20) was used to define the data type for s_last in the Student table. How many
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characters will Oracle save to the disk if the user enters illia as the student’s last name?
Character Data Types (continued)
Unicode coding
– Standardized technique that provides way to encode
data in diverse languages
NVARCHAR2
– Counterpart of VARCHAR2
– Uses Unicode coding
NCHAR
– Counterpart of CHAR
– Uses Unicode encoding
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Number Data Types
NUMBER
– Used for all numeric data
– Syntax
# of digits both to left and
right of decimal point
• columnname NUMBER [([precision,]
[scale])]
# of digits on the right side of decimal point
Example:
– s_balance NUMBER (5,2)
– s_gpa NUMBER (3,2)
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Number Data subtypes
Integer number syntax
Just the precision. No scale specified
– columnname NUMBER(precision)
Fixed-point number
– Contains specific number of decimal places
– Column declaration specifies both precision and scale
– Example: price NUMBER(5,2)
Floating-point number
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Contains variable number of decimal places
Decimal point may appear anywhere (.005, 2.34, etc.)
No precision, no scale
Syntax: columnname NUMBER
Example: s_gpa NUMBER
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Date And Time Data Types
Datetime data subtypes
– Store actual date and time values
– DATE
– TIMESTAMP
 Interval data subtypes
– Store elapsed time interval between two datetime
values
– INTERVAL YEAR TO MONTH
– INTERVAL DAY TO SECOND
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Date And Time Data Types (continued)
DATE
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Stores dates from Dec 31, 4712 BC to Dec 31, AD 4712
Default date format: DD-MON-YY
Default time format: HH:MI:SS AM
Syntax: columnname DATE
TIMESTAMP
– Stores date values similar to DATE data type
– Also stores fractional seconds
If omitted, default is 6 decimal place
– Syntax: columnname TIMESTAMP
(fractional_seconds_precision)
– Example: shipment_date TIMESTAMP(2) 13
Date And Time Data Types (continued)
INTERVAL YEAR TO MONTH
– Stores time interval expressed in years and months
using the following syntax:
+|– elapsed_years-elapsed_months
– Example: +02-11 specifies 2 years and 11 months
– Example:
time_enrolled INTERVAL YEAR TO MONTH
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Date And Time Data Types (continued)
INTERVAL DAY TO SECOND
– Stores time interval expressed in days, hours, minutes,
and seconds using the following syntax:
Max allowed number of digits used to
express the elapsed days
Columnname INTERVAL DAY [(leading_precision)]
TO SECOND [(fractional_seconds_precision)]
Max allowed number of digits used to
express the elapsed seconds
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Large Object (LOB) Data Types
Store binary data such as:
– Digitized sounds or images
– References to binary files from word processor or
spreadsheet
General syntax
– columnname Lob_data_type
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Constraints
Table constraint
– Restricts data value with respect to all other values in
table like primary key must be unique, not NULL.
Column constraint
– Limits value that can be placed in specific column
– Irrespective of values that exist in other table rows
Types of constraints:
– Integrity constraints
– Value constraints
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Constraints (cont.)
Constraint naming convention
– tablename_columnname_constraintid
Constraint definitions should be placed either:
– At end of CREATE TABLE command after table
columns declared
– Within each column definition
Example:
CREATE TABLE location
(loc_id NUMBER(6),
Room VARCHAR2(6),
CONSTRAINT location_loc_id_pk PRIMARY KEY (loc_id);
CREATE TABLE location
(loc_id NUMBER(6)
CONSTRAINT location_loc_id_pk PRIMARY KEY),
Room VARCHAR2(6);
Q: Is there any syntax error (or something missing in the above CREATE TABLE statements?
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Integrity Constraints
Primary key
– Syntax (within table definition)
• CONSTRAINT constraint_name PRIMARY
KEY
CREATE TABLE location
(loc_id NUMBER(6)
CONSTRAINT location_loc_id_pk PRIMARY KEY),
Room VARCHAR2(6));
– Syntax (at end of table definition)
• CONSTRAINT constraint_name PRIMARY
KEY (columnname)
CREATE TABLE location
(loc_id NUMBER(6),
Room VARCHAR2(6),
CONSTRAINT location_loc_id_pk PRIMARY KEY (loc_id));
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Integrity Constraints (continued)
Foreign key
– Column constraint
– Specifies that value user inserts in column must exist
as primary key in referenced table
– Syntax (placed at end of table definition)
CONSTRAINT constraint_name
FOREIGN KEY (columnname)
REFERENCES primary_key_tablename
(primary_key_columnname)
– Example of foreign key defined in the Faculty table:
CONSTRAINT faculty_loc_id_fk
FOREIGN KEY (loc_id)
REFERENCES location (loc_id)
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Integrity Constraints (continued)
Foreign key (continued)
– Syntax (placed within table definition)
CONSTRAINT constraint_name
REFERENCES primary_key_tablename
(primary_key_columnname)
– Example:
loc_id NUMBER(6) CONSTRAINT faculty_loc_id_fk
REFERENCES location (loc_id)
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Integrity Constraints (continued)
Composite key
– Syntax
CONSTRAINT constraint_name
PRIMARY KEY (columnname1, columnname2 …)
– Example:
CREATE TABLE enrollment
(s_id NUMBER(5) CONSTRAINT enrollment_s_id_fk REFERENCES student(s_id),
c_sec_id NUMBER(8) CONSTRAINT enrollment_c_sec_id_fk REFERENCES
course_section(c_sec__id),
CONSTRAINT enrollment_s_id_c_sec_id_pk PRIMARY KEY (s_id, c_sec_id));
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Value Constraints
Value constraints
– Column-level constraints
– Restrict data values that users can enter
– Commonly used value constraints
• CHECK conditions
• DEFAULT constraint
CONSTRAINT student_s_class_cc
CHECK ((s_class = ‘FR’) OR (s_class = ‘SO’)
OR (s_class = ‘JR’) OR (s_class = ‘SR’))
NOT NULL constraint
● UNIQUE constraint
●
s_state CHAR(2) DEFAULT ‘FL’
CONSTRAINT course_credits_cc
CHECK ((credits > 0) AND (credits < 12))
S_last VARCHAR2(30)
CONSTRAINT student_s_last_nn NOT NULL
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