Changing a column Datatype length in Teradata

The options for changing or modifying the length of a datatype are limited in Teradata.
However, we can use the below code for changing the length only for VARCHAR types.

To modify a column type, length or format, we can use ADD function in Teradata
ALTER TABLE Table_Name
ADD Existing_Column_Name  New_Data_Type(New_Length)


Examples:
Consider that Employee_Name is now with VARCHAR(20)
ALTER TABLE tbl_emp
ADD Employee_Name  VARCHAR(50)


To modify the data type from CHAR to INT or to decrease the size of VARCHAR column, the table has to be dropped and re-created.

The below examples are for unsuccessful cases
CHAR ( FROM CHAR (5) TO CHAR (7)) - - syntax error - 3558
TIMESTAMP ( FROM TIMESTAMP(0) TO TIMESTAMP(1) )- syntax error - 3558
DECIMAL (FROM DECIMAL(15,0) TO DECIMAL(15,1) )- syntax error - 3558
INTEGER ( FROM INTEGER TO DECIMAL(15,0)) - syntax error - 3558