This document discusses how to manage tables in a database including creating, modifying, and dropping tables. The key points are: 1. A table stores data in rows and columns and is created using the CREATE TABLE statement. 2. Tables can be modified using the ALTER TABLE statement to add, modify, or drop columns and constraints. 3. Integrity constraints like primary keys, foreign keys, checks and defaults are applied to tables to maintain data integrity. 4. External tables allow querying data stored outside the database in flat files and are created using the CREATE TABLE statement with the ORGANIZATION EXTERNAL clause.

1. Managing Databases and Tables
Ms. Amrit Kaur
gamritkaur@live.com

2. 1. MANAGE TABLES

3. 1.1 What is a Table?
• A TABLE is database objects used to store
data.
• Data in a table is organized in rows and
columns.
– Row represents Record or Tuples
– Column represents Fields or Attributes

4. 1.2 CREATING A TABLE
CREATE TABLE tablename
(
column1 datatype (size) [DEFAULT expression]
[CONSTRAINT constraint_name constraint_type]
,
column2 datatype (size) [DEFAULT expression]
[CONSTRAINT constraintname constrainttype ],
....
)

5. CREATING A Table using Query
CREATE TABLE tablename AS
SELECT statement

6. Modifying a Table
• Modify Tables to
– Add new column
– Change data type of a column
– Add or remove constraints on existing column
• ALTER statement is used to modify table
structure.

7. Modifying a Table
• To Add Column
ALTER TABLE table_name
ADD column_name column-definition;
• To Modify Column Definition
ALTER TABLE table_name
MODIFY column_name column-definition;

8. Modifying a Table
• To Delete column
ALTER TABLE table_name
DROP COLUMN column_name;
• To Rename column
ALTER TABLE table_name
RENAME COLUMN old_col_name TO new_column_name;

9. Modifying a Table
• To Enable Constraint
ALTER TABLE table_name
ENABLE CONSTRAINT constraint_name;
• To Disable Constraint
ALTER TABLE table_name
DISABLE CONSTRAINT constraint_name;

10. Dropping a Table
• DROP TABLE statement is used to delete
table.
DROP TABLE table_name;
• Dropping a table means deleting
– Data
– Table definition
– Associated database objects like index, triggers,
constraints etc.

11. Dropping a Table
• NOTE:
– If table is referenced, referenced table and
constraints must be deleted explicitly before
deleting a table.

12. Rename Table
• RENAME statement is used to change the
name of the table.
RENAME TABLE old_table_name TO new_table_name
RENAME TABLE statement is not allowed if there are any open
cursors that reference the table that is being altered.

13. Data stored in a table is complete &
consistent.NO ONE enters invalid data in it.
Ensure

14. • Maintaining consistency and completeness of
data is called data integrity.
• In Oracle, we maintain data integrity by
– Applying constraints
– Enabling and disabling constraints
– Non-declarative approach using database triggers

15. Applying Constraints
• Constraints applied to a column maintain data
integrity referred as Integrity Constraints.
• Constraints Can Be Created either using
– CREATE TABLE statement
– ALTER TABLE statement

16. Applying Constraints
• Constraints divided into
– Primary Key constraint
– Unique constraint
– Foreign Constraint
– Check Constraint
– Default Constraint

17. Applying Constraint – NOT NULL
• By default, all columns in a table allow nulls.
• A NOT NULL constraint requires a column of a
table contain no null values.

18. Applying Constraint - UNIQUE
• Use to enforce uniqueness (entity integrity) on
non-primary columns.
• It ensures no two rows of a table have duplicate
values in a specified column(s).
CREATE TABLE tablename
( column1 datatype (size) [CONSTRAINT constraint_name]
UNIQUE,
column2 datatype (size) [CONSTRAINT constraintname]
UNIQUE], ....
)

19. Applying Constraint - UNIQUE
• PRIMARY KEY vs UNIQUE
– Primary key cannot contain NULL values whereas
one NULL row is allowed for Unique constraint.
– Single primary key can be created on a table
whereas a table can contain Multiple unique
constraints.

20. Applying Constraint – PRIMARY KEY
• A primary key constraint is defined on a
column or set of columns whose value
uniquely identify all the rows in a table.
• A primary key column CANNOT contain NULL
values.

21. Applying Constraint – PRIMARY KEY
• Applying Primary Key while creating table
CREATE TABLE tablename
( column1 datatype (size) [CONSTRAINT
constraint_name] PRIMARY KEY ,
column2 datatype (size) [CONSTRAINT
constraintname constraint_name], .... )

22. APPLYING CONSTRAINT – Foreign Key
• Used to enforce Referential Integrity.
• Removes inconsistency in two tables when the
data in one table depends on the data in
another table.
• Always refers the primary key of another
table.

23. Applying CONSTRAINT – Foreign Key
• Syntax
CREATE TABLE tablename
( column1 datatype (size) REFERENCES tablename
(columnname) [DELETE CASCADE | DELETE
SET NULL],
column2 datatype (size) [CONSTRAINT constraintname
constraint_name], .... )

24. Applying CONSTRAINT – Foreign Key
• Actions defined by Referential Integrity
Constraint
– Update and Delete No Action (DEFAULT)
• if a primary key value is referenced by a value in the
foreign key, then the referenced primary key value
CANNOT be deleted or updated.
– Delete CASCADE
• When rows in a parent table is deleted, all rows in child
tables with dependent foreign key values also deleted.

25. Applying CONSTRAINT – Foreign Key
• Actions defined by Referential Integrity
Constraint
– Delete SET NULL
• When rows in a parent table is deleted, all rows in child
tables with dependent foreign key values set to NULL.

26. Applying CONSTRAINT - CHECK
• CHECK constraint enforce domain integrity by
restricting values to be inserted in a column.
CREATE TABLE tablename
( column1 datatype (size) [CONSTRAINT constraint_name]
CHECK (coulumn name check condition), ...... )
• Multiple CHECK constraint can be defined on a
single column.
Expression include elements such as arithmetic
operators, relational operators, keyword such as IN, LIKE
and BETWEEN.
Condition Limitations
• It must be a Boolean expression evaluated using the
values in the row being inserted or updated
•
• It cannot contain subqueries; sequences; the SQL
functions SYSDATE, UID, USER, or USERENV

27. Applying Constraint - CHECK
• Restrictions on CHECK constraint
– You cannot specify a check constraint for a view.
– The check condition can refer to any column in the
table, but it cannot refer to columns of other tables.
– Conditions of check constraints cannot contain
• Subqueries
• Calls to user-defined functions
• Nested table columns or attributes
• Date constants that are not fully specified

28. Applying Constraint - DEFAULT
• DEFAULT constraint is used to assign constant
value to a column.
• One DEFAULT constraint can be created for a
column.
CREATE TABLE tablename
( column1 datatype (size) [CONSTRAINT constraint_name]
DEFAULT (constant expression | NULL),
column2 datatype (size) [CONSTRAINT constraintname]
DEFAULT (constant expression | NULL], ....
)

29. Create Directory
• CREATE DIRECTORY statement is used to
create directory object.
• Directory object specify alias for directory on
the server where external binary files and
external table data are located.
• Use directory names when referring to files
rather than hard coding the OS path

30. CREATE DIRECTORY
• You must have CREATE ANY DIRECTORY system
privilege to create directories.
• Automatically granted READ and WRITE object
privileges on directory.
• Maximum length of directory name is 30 bytes

31. CREATE DIRECTORY
CREATE OR REPLACE DIRECTORY directory_name
AS ‘pathname’;
CREATE OR REPLACE DIRECTORY mydir AS
‘/usr/bin.bfile_dir

32. CREATING AND QUERYING
EXTERNAL TABLES

33. External Tables
• External Tables allow Oracle to query data that
is stored outside the database in flat files.
• They can be used for query, join and sort
operations.
• Views can be created against external tables.
• Prior to Oracle Database10g, external table
were read only. External Tables can also be
written to.

34. How External Tables Are Created?
• SQL CREATE TABLE .... ORGANISATION
EXTERNAL statement is used to create
external tables.
• Specify Attributes
– TYPE:
• ORACLE_LOADER (Text Files)
• ORACLE_DATAPUMP (binary Files)
– DEFAULT DIRECTORY
• Directory object is used not path

35. How External Tables Are Created?
• Specify Attributes
– ACCESS PARAMETERS:
• External data source
– LOCATION
• Specifies the location of external data.

36. Steps of Creating External table
• Create directory
CREATE directory extTabData AS ‘/app/data’;
GRANT READ ON DIRECTORY TO SCOTT;
• Create Traditional Table
CREATE TABLE emp (empno number, name char(20));

37. Steps of Creating External table
• Create external table
CREATE TABLE empExternal
(empno number, name char(20))
ORGANIZATION EXTERNAL
( TYPE ORACLE_LOADER
DEFAULT DIRECTORY extTabData
ACCESS PARAMETERS
(RECORD DELIMITED BY NEW LINE
FIELDS (empno number , name char(20))
)
LOCATION(‘filename.dat’)
)

38. Steps of Creating External Table
• LOAD data from external table to traditional
table
INSERT INTO emp (empno,name)
SELECT empno,name FROM empExternal
• Now traditional table can be queried.