- The fact that ALTER TYPE> requires rewriting the whole table
+ The fact that SET DATA TYPE> requires rewriting the whole table
is sometimes an advantage, because the rewriting process eliminates
any dead space in the table. For example, to reclaim the space occupied
by a dropped column immediately, the fastest way is:
- The USING option of ALTER TYPE> can actually
+ The USING option of SET DATA TYPE> can actually
specify any expression involving the old values of the row; that is, it
can refer to other columns as well as the one being converted. This allows
- very general conversions to be done with the ALTER TYPE>
+ very general conversions to be done with the SET DATA TYPE>
syntax. Because of this flexibility, the USING
expression is not applied to the column's default value (if any); the
result might not be a constant expression as required for a default.
This means that when there is no implicit or assignment cast from old to
- new type, ALTER TYPE> might fail to convert the default even
+ new type, SET DATA TYPE> might fail to convert the default even
though a USING clause is supplied. In such cases,
drop the default with DROP DEFAULT>, perform the ALTER
TYPE>, and then use SET DEFAULT> to add a suitable new