Chapter 8
Table Creation and Management
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Chapter Objectives
• Create a new table using the CREATE
TABLE command
• Name a new column or table
• Use a subquery to create a new table
• Add a column to an existing table
• Modify the size of a column in an existing
table
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Chapter Objectives
• Drop a column from an existing table
• Mark a column as unused, then delete it at a
later time
• Rename a table
• Truncate a table
• Drop a table
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Database Table
•
•
•
•
A database object
Stores data for the database
Consists of columns and rows
Created and modified through Data
Definition Language (DDL) commands
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Table and Column Names
• Maximum 30 characters - no blank spaces
• Must begin with a letter
• Can contain numbers, underscore (_), and
number sign (#)
• Must be unique
• No reserved words allowed
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Common Datatypes
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CREATE TABLE Command
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CREATE TABLE Command
• Column definition list must be enclosed in
parentheses
• Datatype must be specified for each column
• Maximum of 1,000 columns
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CREATE TABLE Command
Example
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DESCRIBE Command
Displays structure of specified table
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Table Creation Through
Subqueries
• Can use subquery to retrieve data from
existing table
• Requires use of AS keyword
• New column names can be assigned
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CREATE TABLE…AS
Command
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CREATE TABLE…AS
Command Example
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Modifying Existing Tables
• Accomplished through ALTER TABLE
command
• Use ADD clause to add a column
• Use MODIFY clause to change a column
• Use DROP COLUMN to drop a column
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ALTER TABLE Command
Syntax
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ALTER TABLE…ADD
Command Example
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ALTER TABLE…MODIFY
Command Example
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Modification Guidelines
• Column must be as wide as the data it
already contains
• If a NUMBER column already contains
data, size cannot be decreased
• Adding or changing default data does not
affect existing data
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ALTER TABLE…DROP
COLUMN Command
• Can only reference one column per
execution
• Deletion is permanent
• Cannot delete last remaining column in a
table
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ALTER TABLE…SET UNUSED
Command
• Once marked for deletion, column cannot
be restored
• Storage space freed at later time
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ALTER TABLE…DROP
UNUSED Command
Frees up storage space from columns
previously marked as unused
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RENAME Command
Used to rename a table – old name no longer valid
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Truncating a Table –
TRUNCATE Command
Rows are deleted - structure of table remains
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DROP TABLE Command
Table structure and contents are deleted
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