The database system searches for the data to be changed by an UPDATE statement in the B* tree in the same way as for a SELECT statement.
· If an UPDATE is executed and the primary key remains unchanged, then only the content of the table rows is changed.
· If the data length changes, then the items of the succeeding entries and their addresses are changed in the position list in the leaf page in the B* tree.
· If the key field changes, then the UPDATE is listed as a DELETE with a subsequent INSERT.