ALTER TABLE BAT$RECEIPT$RECEIPT DROP ABOUT_EXEC_PROC;

ALTER TABLE BAT$RECEIPT$RECEIPT ADD ABOUT_EXEC_PROC /* CHAR(3) */ COMPUTED BY ('___');

A column defined as COMPUTED BY <expression> can now be altered using the ALTER TABLE...ALTER
COLUMN syntax. This feature can be used only to change the <expression> element of the column definition
to a different expression. It cannot convert a computed column to non-computed or vice versa.