Hello,
I'm trying to write a trigger on insert which should insert the row
in another
table. The table on which to insert the row should be selected at
runtime and
it is not know in advance. For example, let's say we have a table with
two columns, a date and an integer. a row is inserted into table XXX and
CREATE TABLE XXX
(
refdate date;
x2 integer;
)
when the statement
insert into XXX VALUES ('2007-11-11', 1);
is executed, a trigger (or rule) should be fired to insert the row into
table XXX_20071111 (having the same schema). If the XXX_* tables are
created beforehand
this is not a problem because you can set up a rule for each date
performing
the needed insert (as documented in http://www.postgresql.org/docs/
8.1/interactive/ddl-partitioning.html)
The problem arises when you try to extend the trigger in order to
also dinamically
perform table creation is the XXX_20071111 doesn't exist:
I have, for example:
CREATE OR REPLACE FUNCTION add_child_table(parent_name varchar, d date)
RETURNS varchar AS $$
DECLARE
new_table_name varchar;
BEGIN
raise notice '%', 'creating table';
new_table_name := date2tblname(parent_name, d); -- converts
table name and date into child table name
execute 'CREATE TABLE ' || new_table_name || ' ( ) INHERITS
(' || parent_name || ')';
execute 'CREATE RULE '
|| new_table_name
|| '_insert AS ON INSERT TO '
|| parent_name
|| ' WHERE ( refdate = DATE ' /* refdate is the
field we use to partition */
|| '''' || d || ''''
|| ' ) DO INSTEAD INSERT INTO '
|| new_table_name
|| ' VALUES ( NEW.* )';
return new_table_name;
END;
$$ LANGUAGE plpgsql;
I can use the above to add a child table and the rule to implement
partitioning
CREATE OR REPLACE FUNCTION child_creation_trigger()
RETURNS "trigger" AS $$
BEGIN
IF ( child_exist(TG_RELNAME::text, NEW.refdate) = false ) THEN
raise notice '%', 'creating ' || TG_RELNAME::text || '
for ' || NEW.refdate::text;
perform add_child_table(TG_RELNAME::text, NEW.refdate);
--insert into ' || child_table_name || ' values
( NEW.* );
RETURN NEW;
ELSE
raise notice '%', 'NOT creating ' || TG_RELNAME::text
|| ' for ' || NEW.refdate::text;
RETURN NEW;
END IF;
END;
$$ LANGUAGE plpgsql;
The trigger function is hooked to the to-be-partitioned table
CREATE TRIGGER XXX_trigger BEFORE INSERT
ON XXX FOR EACH ROW
execute procedure child_creation_trigger ();
now, every time I insert a tuple into XXX, the trigger is fired and
checks if the needed table exists or
not. If not, it creates the table and rule and goes on. The problem
is that in this case the first
row is inserted into the XXX table, not in the (just created)
XXX_<refdate> . Then I tried to insert
the row myself from the trigger body (and return null in order to
skip the original insertion), but
I'm not able to do it (see the commented insert in the above IF
clause) because I can't properly
quote the target table name.
I shoud perform a
insert into child_table_name values (NEW.*);
obviously written like this the plpgsql complains at runtime because
child_table_name is not a table name.
If, on the other side, I dynamically create the query like in
execute 'insert into ' || child_table_name || ' values (NEW.*)';
it complains because NEW in the execution context is unknown.
This should be a rather common problem... Isn't it? Is there a
canonical way to
solve it? Maybe there's a trivial answer, but I have no plpgsql
programming
experience.
Thanks a lot in advance,
Enrico Sirola
[EMAIL PROTECTED]
