// Add new column with column constraints
EXEC SQL
ALTER TABLE customer ADD COLUMN timeref char(8)
CHECK validtime(timeref)
ERROR "Not a valid time string";
 
// Alter existing columns to add column constraints
EXEC SQL
ALTER TABLE customer
ALTER COLUMN available CALCULATED limit-balance
ALTER COLUMN limit RECALCULATE
ALTER COLUMN balance RECALCULATE;
 
//or
EXEC SQL
ALTER TABLE customer
ALTER (available CALCULATED limit-balance,
limit RECALCULATE,
balance RECALCULATE);
 
// Add new column, add column constraint,
// modify column datatype and drop constraints then drop column
EXEC SQL
ALTER TABLE customer ADD (timeref char(8));
 
EXEC SQL
ALTER TABLE customer
ALTER CONSTRAINT
(timeref SET CHECK validtime(timeref)
ERROR "Not a valid time string");
 
EXEC SQL
ALTER TABLE customer
ALTER (timeref datetime)
DROP CONSTRAINT (timeref CHECK, timeref ERROR);
 
EXEC SQL
ALTER TABLE customer DROP (timeref);
 
// Add an ONUPDATE table constraint 
EXEC SQL
ALTER TABLE customer
MODIFY ONUPDATE "do check_update";
 
// Add and then remove CHECK table constraint
EXEC SQL
ALTER TABLE customer SET CHECK checkit() error "Invalid operation";
 
set sql off
use customer
display dictionary
edit  && Save and Exit will call validation
use
 
EXEC SQL 
ALTER TABLE customer DROP CHECK;
 
// Rename column
EXEC SQL
ALTER TABLE customer RENAME(first_name,forename);