HP 3000 Manuals HP 3000 Manuals
Maintaining Sets of Interrelated Objects
If your databases contain tables that are interrelated through rules and
procedures or integrity constraints, the job of maintaining them may be
more difficult. As you begin to restructure a database, be sure to study
the implications of loading and unloading, dropping and recreating
objects that have relationships to other objects. The following are a
few common situations that can lead to unexpected results:
* Dropping a unique constraint also drops the B-tree index that
supports the constraint and deprives the optimizer of one access
path to the data in the table.
* Attempting to drop a table that is referenced by another table
results in an error. You must drop the constraint that links the
two tables, or else drop the referencing table first. To drop the
constraint, use the DROP CONSTRAINT clause in the ALTER TABLE
statement, specifying the referencing table.
* Dropping a table results in dropping of constraints and rules
built on it. If you are restructuring, and you wish to drop and
recreate the table, you must also recreate the rules and
constraints.
* Dropping a procedure does not drop rules that invoke the
procedure, but it does invalidate stored sections that depend on
invoking the procedure from a rule. The loss of the procedure
will be reported as an error when there is an attempt to
revalidate those sections. If you wish to drop rules associated
with a particular procedure, you should do so explicitly with DROP
RULE statements.
* A complex chaining set of rules and procedures will be disrupted
by the dropping of any rule or procedure in the chain. If you are
using rule chaining, it is your responsibility to control the
inventory of rules and procedures carefully.