HP 3000 Manuals HP 3000 Manuals
Understanding Implicit Updatability
The FIPS 127.1 standard does not allow a FOR UPDATE clause in a DECLARE
CURSOR statement. In this standard, updatability of a cursor rests
solely on the cursor definition. In contrast, ALLBASE/SQL default
processing (i.e., flagging is not in effect) of a DECLARE CURSOR
statement having no FOR UPDATE clause is to allow neither update nor
delete on any column in the cursor definition.
When the FIPS flagger is set and a FOR UPDATE clause is not specified,
standard updatability processing takes effect. That is, any column in
the cursor's select list can be updated or deleted. This is known as
implicit updatability. When implicit updatability is in effect, a
performance impact may be realized as compared to ALLBASE/SQL default
processing, as follows:
* An index scan can only be applied to an EQUAL predicate containing
an index column. An index scan is suppressed for a predicate
containing a range factor.
* More severe locks (intent update) are required. Therefore, if the
cursor is to be used only for reading data, unnecessary locking
overhead my be incurred. To alleviate this type of overhead, a
FOR READ ONLY clause can be used when declaring the cursor.
Note that when the FIPS flagger is set and a FOR UPDATE clause is used in
the cursor definition, a warning message is generated, and ALLBASE/SQL
default processing overrides the semantics of the standard.