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Database Managment - Oracle

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Lesson Description


Lession - #1405 Oracle ALTER TABLE


Oracle ALTER TABLE Statement

In Oracle, ALTER TABLE explanation determines how to add, change, drop or erase sections in a table. Renaming a table is likewise utilized.

Syntax:

ALTER TABLE table_name  
  ADD column_name column-definition;   

Example

ALTER TABLE customers  
  ADD customer_age varchar2(50>
;

How to add multiple columns in the existing table

Syntax:

ALTER TABLE table_name  
  ADD (column_1 column-definition,  
       column_2 column-definition,  
       ...  
       column_n column_definition>
;

Example

ALTER TABLE customers  
  ADD (customer_type varchar2(50>
, customer_address varchar2(50>
>
;

Output:

Now, two columns customer_type and customer_address will be added in the table customers.


How to modify column of a table

Syntax:

ALTER TABLE table_name  
  MODIFY column_name column_type;   

Example:

ALTER TABLE customers  
  MODIFY customer_name varchar2(100>
not null;


Now the column column_name in the customers table is modified
to varchar2 (100>
and forced the column to not allow null values.


How to modify multiple columns of a table

Syntax:

ALTER TABLE table_name  
  MODIFY (column_1 column_type,  
          column_2 column_type,  
          ...  
          column_n column_type>
;

Example:

ALTER TABLE customers  
  MODIFY (customer_name varchar2(100>
not null, city varchar2(100>
>
;


This will modify both the customer_name and city columns in the table. 


How to drop column of a table

Syntax:

ALTER TABLE table_name  
  DROP COLUMN column_name;  

Example:

ALTER TABLE customers  
  DROP COLUMN customer_name;  


This will drop the customer_name column from the table.


How to rename column of a table

Syntax:

ALTER TABLE table_name  
  RENAME COLUMN old_name to new_name;  

Example:

ALTER TABLE customers  
 RENAME COLUMN customer_name to cname;  


This will rename the column customer_name into cname.