Check out example codes for "alter table modify column". It will help you in understanding the concepts better.

Code Example 1

-- ORACLE 18c
ALTER TABLE table_name 
MODIFY column_name datatype;

-- Example
ALTER TABLE product
MODIFY description VARCHAR2(500 char);

Code Example 2

ALTER TABLE table_name
ALTER COLUMN column_name datatype;
--ex.
ALTER TABLE Customers
ADD Email varchar(255);

Code Example 3

ALTER TABLE table_name
ALTER COLUMN column_name datatype;

Code Example 4

ALTER TABLE table_name
ALTER COLUMN column_name datatype;

-- Example
ALTER TABLE product
ALTER COLUMN description VARCHAR(250);

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