1. Chapter 2: Creating And Modifying Database Tables
Guide to Oracle 10g

2. Objectives After completing this chapter, you should be able to:
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
Debug Oracle 10g SQL commands and use online help resources available through the Oracle Technology Network (OTN)
Guide to Oracle 10g

3. Objectives (continued)
View information about your database tables using Oracle 10g data dictionary views
Modify and delete database tables using SQL*Plus
Guide to Oracle 10g

4. 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
Most recent version
Guide to Oracle 10g

5. Introduction to SQL (continued)
Structured query language (SQL) (continued)
Basic categories for SQL commands
Data definition language (DDL)
Data manipulation language (DML)
Reserved words
SQL command words
Guide to Oracle 10g

6. Oracle 10g User Accounts User account User schema Database objects
Created for each user
Identified using unique username and password
User schema
Area of database belonging to user
Database objects
Also called schema objects
Objects in user schema
Guide to Oracle 10g

7. Defining Oracle 10g Database Tables
Primary data objects in relational database
Constraints
Restrictions on data values that column can store
Oracle naming standard
Rules that Oracle corporation has established for naming all database objects
Guide to Oracle 10g

8. Defining Oracle 10g Database Tables (continued)
Oracle naming standard
One to 30 characters long
Contain letters, numbers, and special symbols $, _, and #
Begin with character
CREATE TABLE SQL syntax
CREATE TABLE tablename
(columnname1 data_type,
columnname2 data_type, …)
Guide to Oracle 10g

9. Oracle 10g Data Types Data type
Specifies kind of data that column stores
Provides means for error checking
Enable DBMS to use storage space more efficiently
Basic types
Character
Number
Date/time
Large object
Guide to Oracle 10g

10. Character Data Types VARCHAR2 CHAR Variable-length character data
Syntax
columnname VARCHAR2(maximum_size)
CHAR
Fixed-length character data
columnname CHAR[(maximum_size)]
Guide to Oracle 10g

11. Character Data Types (continued)
Unicode
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
Guide to Oracle 10g

12. Number Data Types NUMBER Precision Used for all numeric data Syntax
columnname NUMBER [([precision,] [scale])]
Precision
Total number of digits both to left and right of decimal point
Guide to Oracle 10g

13. Number Data Types (continued)
Integer number syntax
columnname NUMBER(precision)
Fixed-point number
Contains specific number of decimal places
Column declaration specifies both precision and scale
Example
price NUMBER(5, 2)
Guide to Oracle 10g

14. Number Data Types (continued)
Floating-point number
Contains variable number of decimal places
Syntax
columnname NUMBER
Example
s_gpa NUMBER
Guide to Oracle 10g

15. 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
Guide to Oracle 10g

16. Date And Time Data Types (continued)
Stores dates from December 31, 4712 BC to December 31, AD 4712
Default date format
DD-MON-YY
Default time format
HH:MI:SS AM
Syntax:
columnname DATE
Guide to Oracle 10g

17. Date And Time Data Types (continued)
TIMESTAMP
Stores date values similar to DATE data type
Also stores fractional seconds
Syntax
columnname TIMESTAMP (fractional_seconds_precision)
Guide to Oracle 10g

18. Date And Time Data Types (continued)
INTERVAL YEAR TO MONTH
Stores time interval expressed in years and months
Syntax
+|– elapsed_years-elapsed_months
Guide to Oracle 10g

19. Date And Time Data Types (continued)
INTERVAL DAY TO SECOND
Stores time interval expressed in days, hours, minutes, and seconds
Syntax
+|– elapsed_days elapsed_hours:elapsed_minutes:elapsed_seconds
Guide to Oracle 10g

20. 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
Guide to Oracle 10g

21. Large Object (LOB) Data Types (continued)
Guide to Oracle 10g

22. Constraints
Rules that restrict data values that can be entered into column
Types of constraints:
Integrity constraints
Value constraints
Table constraint
Restricts data value with respect to all other values in table
Guide to Oracle 10g

23. Constraints (continued)
Column constraint
Limits value that can be placed in specific column
Irrespective of values that exist in other table rows
Constraint definitions should be placed either:
At end of CREATE TABLE command after table columns declared
Within each column definition
Guide to Oracle 10g

24. Constraints (continued)
Constraint naming convention
tablename_columnname_constraintid
Guide to Oracle 10g

25. Common ConstraintID Abbreviations
Guide to Oracle 10g

26. Integrity Constraints
Primary key
Syntax (within table definition)
CONSTRAINT constraint_name PRIMARY KEY
Syntax (at end of table definition)
CONSTRAINT constraint_name PRIMARY KEY (columnname)
Guide to Oracle 10g

27. 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)
Guide to Oracle 10g

28. Integrity Constraints (continued)
Foreign key (continued)
Syntax (placed within table definition)
CONSTRAINT constraint_name
REFERENCES primary_key_tablename
(primary_key_columnname)
Composite key
Syntax
PRIMARY KEY (columnname1, columnname2 …)
Guide to Oracle 10g

29. Integrity Constraints (continued)
Value constraints
Column-level constraints
Restrict data values that users can enter
Commonly used value constraints
CHECK conditions
NOT NULL constraint
DEFAULT constraint
UNIQUE constraint
Guide to Oracle 10g

30. Creating Database Tables Using SQL*Plus
Start SQL*Plus
Type username and password
Type SQL commands at SQL prompt
End each command with semicolon (;)
Press Enter to submit commands
Guide to Oracle 10g

31. Creating Database Tables Using SQL*Plus (continued)
SQL*Plus interpreter
Checks command for syntax errors
Submits command to database
SQL commands are not case sensitive
When creating database tables that contain foreign key references
Must first create table in which foreign key is primary key
Guide to Oracle 10g

32. SQL Command to Create the LOCATION Table
Guide to Oracle 10g

33. Creating and Editing SQL Commands Using a Text Editor
Good approach for entering commands:
Type commands into text editor such as Notepad
Copy commands, then paste into SQL*Plus
Execute commands
Script
Text file that contains several related SQL commands
Guide to Oracle 10g

34. Using Oracle Online Help Resources to Debug SQL Commands
Syntax error
SQL*Plus interpreter displays error information
Line number within command that caused error
Position of error within line
Error code and description of error
Guide to Oracle 10g

35. Using Oracle Online Help Resources To Debug SQL Commands (continued)
Oracle 10g error codes have:
3-character prefix (such as ORA)
5-digits
Causes of SQL command errors are not always readily apparent
Need to retrieve more information about error
Connect to Oracle Technology Network (OTN) Web Site and search for error code
Guide to Oracle 10g

36. Using Oracle Online Help Resources To Debug SQL Commands (continued)
Last resort debugging technique
Create table multiple times
Each time adding column declaration
Repeat process until you find declaration causing error
Drop table command
To delete table
syntax: DROP TABLE tablename
Guide to Oracle 10g

37. Exiting SQL*Plus Type exit at SQL prompt
Click File on menu bar, and then click Exit
Click Close button on program window title bar
Guide to Oracle 10g

38. Creating a Table with a Foreign Key Constraint
Guide to Oracle 10g

39. Viewing Information about Tables
DESCRIBE command
View column names and data types of table
Syntax
DESCRIBE tablename
Oracle 10g data dictionary
Consists of tables that contain information about structure of database
Guide to Oracle 10g

40. Viewing Information about Tables (continued)
Oracle10g data dictionary (continued)
System creates data dictionary in user schema named SYS
Users do not directly manipulate data dictionary
View
Database object DBMS bases on actual database table
Enables DBMS to present table data in different format based on needs of users
Guide to Oracle 10g

41. Viewing Information about Tables (continued)
Data dictionary views categories
USER
ALL
DBA
Syntax
SELECT view_columnname1, view_columnname2 … FROM prefix_object;
Guide to Oracle 10g

42. Database Objects with Data Dictionary Views
Guide to Oracle 10g

43. Modifying and Deleting Database Tables
Plan tables carefully to avoid having to change structure of database tables later
Unrestricted action
Some specifications of tables can always be modified
Restricted action
Table specifications that can be modified only in certain situations
Guide to Oracle 10g

44. Unrestricted Actions when Modifying Database Tables
Guide to Oracle 10g

45. Deleting and Renaming Existing Tables
DROP TABLE command
Delete table
Syntax
DROP TABLE tablename;
DROP TABLE tablename CASCADE CONSTRAINTS;
Guide to Oracle 10g

46. Deleting and Renaming Existing Tables (continued)
RENAME TO command
Syntax
RENAME old_tablename TO new_tablename;
Guide to Oracle 10g

47. Adding Columns to Existing Tables
Add new column to table
Syntax
ALTER TABLE tablename
ADD(columnname data_declaration constraints);
Guide to Oracle 10g

48. Modifying Existing Column Data Definitions
Modify existing column’s data declaration
Syntax
ALTER tablename
MODIFY(columnname new_data_declaration);
Guide to Oracle 10g

49. Deleting a Column Data stored in deleted column removed from database
Syntax
ALTER TABLE tablename
DROP COLUMN columnname;
Guide to Oracle 10g

50. Renaming a Column Syntax ALTER TABLE tablename
RENAME COLUMN old_columnname TO new_columnname;
Guide to Oracle 10g

51. Adding and Deleting Constraints
Add constraint to existing table
Syntax
ALTER TABLE tablename
ADD CONSTRAINT constraint_name constraint_definition;
Remove existing constraint
DROP CONSTRAINT constraint_name;
Guide to Oracle 10g

52. Enabling and Disabling Constraints
Constraint enabled
DBMS enforces constraint when users attempt to add new data to database
Disable existing constraint syntax
ALTER TABLE tablename
DISABLE CONSTRAINT constraint_name;
Enable existing constraint syntax
ENABLE CONSTRAINT constraint_name;
Guide to Oracle 10g

53. Summary SQL commands include
Data description language (DDL) commands
Data manipulation language (DML) commands
Each user account owns table and data objects in own area of database
Called user schema
When creating database table specify table name, column names, data type, and column sizes
Guide to Oracle 10g

54. Summary (continued)
Constraints restrict data values that users can enter into database columns
When SQL commands have errors interpreter reports:
Line number
Position of character causing error
Returns error code and description
Use describe command to display table info
Guide to Oracle 10g