The PostgreSQL server returns a command
status string, such as INSERT 149592 1, for each
query it receives. This is simple enough when there are no rules
involved, but what happens when the query is rewritten by rules?
As of PostgreSQL 7.3, rules affect the
command status as follows:
If there is no unconditional INSTEAD rule for the query, then
the originally given query will be executed, and its command
status will be returned as usual. (But note that if there were
any conditional INSTEAD rules, the negation of their qualifications
will have been added to the original query. This may reduce the
number of rows it processes, and if so the reported status will
be affected.)
If there is any unconditional INSTEAD rule for the query, then
the original query will not be executed at all. In this case,
the server will return the command status for the last query that
was inserted by an INSTEAD rule (conditional or unconditional)
and is of the same type (INSERT, UPDATE, or DELETE) as the original
query. If no query meeting those requirements is added by any
rule, then the returned command status shows the original query
type and zeroes for the tuple-count and OID fields.
The programmer can ensure that any desired INSTEAD rule is the one
that sets the command status in the second case, by giving it the
alphabetically last rule name among the active rules, so that it
fires last.
