Oracle alter table modify column Syntax example

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For complete tips on Oracle alter table syntax, see the book "Easy Oracle Jumpstart".  Oracle provides "alter table" syntax to modify data columns in-place in this form:

alter table
   table_name
modify
   column_name  datatype;

If you are brave you can use a single "alter table" syntax to modify multiple columns:

alter table
   table_name
modify
   (
   column1_name  column1_datatype,
   column2_name  column2_datatype,
   column3_name  column3_datatype,
   column4_name  column4_datatype
   );

Here are some examples of Oracle "alter table" syntax to modify data columns and note that you can add constraints like NOT NULL:

ALTER TABLE 
   customer 
MODIFY 
   ( 
   cust_name varchar2(100) not null,
   cust_hair_color  varchar2(20)
   )
;

We can also use Oracle "alter table" syntax in dynamic PL/SQL to modify data columns

BEGIN 
SQL_STRING := 'ALTER TABLE '||:TABLE_NAME||' MODIFY '||:COLUMN_NAME||' VARCHAR2(100)';

 . . . 
END;