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Postgres FD Implementation
Commit a294726b authored by Tom Lane's avatar Tom Lane
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Incorporate examples and doc patches from Mark Kirkwood and David Fetter.

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doc/src/sgml/plpgsql.sgml
View file @ a294726b
<!--
$PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.55 2005/01/08 22:13:34 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.56 2005/01/14 01:16:22 tgl Exp $
-->
<chapter id="plpgsql">
......@@ -2304,6 +2304,32 @@ SELECT reffunc2();
FETCH ALL IN "&lt;unnamed cursor 1&gt;";
COMMIT;
</programlisting>
</para>
<para>
The following example shows one way to return multiple cursors
from a single function:
<programlisting>
CREATE FUNCTION myfunc(refcursor, refcursor) RETURNS SETOF refcursor AS $$
BEGIN
OPEN $1 FOR SELECT * FROM table_1;
RETURN NEXT $1;
OPEN $2 FOR SELECT * FROM table_2;
RETURN NEXT $2;
RETURN;
END;
$$ LANGUAGE plpgsql;
-- need to be in a transaction to use cursors.
BEGIN;
SELECT * FROM myfunc('a', 'b');
FETCH ALL FROM a;
FETCH ALL FROM b;
COMMIT;
</programlisting>
</para>
</sect3>
......@@ -2585,8 +2611,6 @@ $emp_stamp$ LANGUAGE plpgsql;
CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON emp
FOR EACH ROW EXECUTE PROCEDURE emp_stamp();
</programlisting>
</example>
<para>
......@@ -2646,6 +2670,159 @@ AFTER INSERT OR UPDATE OR DELETE ON emp
FOR EACH ROW EXECUTE PROCEDURE process_emp_audit();
</programlisting>
</example>
<para>
One use of triggers is to maintain a summary table
of another table. The resulting summary can be used in place of the
original table for certain queries &mdash; often with vastly reduced run
times.
This technique is commonly used in Data Warehousing, where the tables
of measured or observed data (called fact tables) can be extremely large.
<xref linkend="plpgsql-trigger-summary-example"> shows an example of a
trigger procedure in <application>PL/pgSQL</application> that maintains
a summary table for a fact table in a data warehouse.
</para>
<example id="plpgsql-trigger-summary-example">
<title>A <application>PL/pgSQL</application> Trigger Procedure For Maintaining A Summary Table</title>
<para>
The schema detailed here is partly based on the <emphasis>Grocery Store
</emphasis> example from <emphasis>The Data Warehouse Toolkit</emphasis>
by Ralph Kimball.
</para>
<programlisting>
--
-- Main tables - time dimension and sales fact.
--
CREATE TABLE time_dimension (
time_key integer NOT NULL,
day_of_week integer NOT NULL,
day_of_month integer NOT NULL,
month integer NOT NULL,
quarter integer NOT NULL,
year integer NOT NULL
);
CREATE UNIQUE INDEX time_dimension_key ON time_dimension(time_key);
CREATE TABLE sales_fact (
time_key integer NOT NULL,
product_key integer NOT NULL,
store_key integer NOT NULL,
amount_sold numeric(12,2) NOT NULL,
units_sold integer NOT NULL,
amount_cost numeric(12,2) NOT NULL
);
CREATE INDEX sales_fact_time ON sales_fact(time_key);
--
-- Summary table - sales by time.
--
CREATE TABLE sales_summary_bytime (
time_key integer NOT NULL,
amount_sold numeric(15,2) NOT NULL,
units_sold numeric(12) NOT NULL,
amount_cost numeric(15,2) NOT NULL
);
CREATE UNIQUE INDEX sales_summary_bytime_key ON sales_summary_bytime(time_key);
--
-- Function and trigger to amend summarized column(s) on UPDATE, INSERT, DELETE.
--
CREATE OR REPLACE FUNCTION maint_sales_summary_bytime() RETURNS TRIGGER AS $maint_sales_summary_bytime$
DECLARE
delta_time_key integer;
delta_amount_sold numeric(15,2);
delta_units_sold numeric(12);
delta_amount_cost numeric(15,2);
BEGIN
-- Work out the increment/decrement amount(s).
IF (TG_OP = 'DELETE') THEN
delta_time_key = OLD.time_key;
delta_amount_sold = -1 * OLD.amount_sold;
delta_units_sold = -1 * OLD.units_sold;
delta_amount_cost = -1 * OLD.amount_cost;
ELSIF (TG_OP = 'UPDATE') THEN
-- forbid updates that change the time_key -
-- (probably not too onerous, as DELETE + INSERT is how most
-- changes will be made).
IF ( OLD.time_key != NEW.time_key) THEN
RAISE EXCEPTION 'Update of time_key : % -&gt; % not allowed', OLD.time_key, NEW.time_key;
END IF;
delta_time_key = OLD.time_key;
delta_amount_sold = NEW.amount_sold - OLD.amount_sold;
delta_units_sold = NEW.units_sold - OLD.units_sold;
delta_amount_cost = NEW.amount_cost - OLD.amount_cost;
ELSIF (TG_OP = 'INSERT') THEN
delta_time_key = NEW.time_key;
delta_amount_sold = NEW.amount_sold;
delta_units_sold = NEW.units_sold;
delta_amount_cost = NEW.amount_cost;
END IF;
-- Update the summary row with the new values.
UPDATE sales_summary_bytime
SET amount_sold = amount_sold + delta_amount_sold,
units_sold = units_sold + delta_units_sold,
amount_cost = amount_cost + delta_amount_cost
WHERE time_key = delta_time_key;
-- There might have been no row with this time_key (e.g new data!).
IF (NOT FOUND) THEN
BEGIN
INSERT INTO sales_summary_bytime (
time_key,
amount_sold,
units_sold,
amount_cost)
SELECT f.time_key,
sum(f.amount_sold),
sum(f.units_sold),
sum(f.amount_cost)
FROM sales_fact f
WHERE f.time_key = delta_time_key
GROUP BY f.time_key;
-- This query can potentially be very expensive if the trigger
-- is created on sales_fact without the time_key indexes.
-- Some care is needed to ensure that this situation does
-- *not* occur.
EXCEPTION
--
-- Catch race condition when two transactions are adding data
-- for a new time_key.
--
WHEN UNIQUE_VIOLATION THEN
UPDATE sales_summary_bytime
SET amount_sold = amount_sold + delta_amount_sold,
units_sold = units_sold + delta_units_sold,
amount_cost = amount_cost + delta_amount_cost
WHERE time_key = delta_time_key;
END;
END IF;
RETURN NULL;
END;
$maint_sales_summary_bytime$ LANGUAGE plpgsql;
CREATE TRIGGER maint_sales_summary_bytime
AFTER INSERT OR UPDATE OR DELETE ON sales_fact
FOR EACH ROW EXECUTE PROCEDURE maint_sales_summary_bytime();
</programlisting>
</example>
</sect1>
<!-- **** Porting from Oracle PL/SQL **** -->
......
doc/src/sgml/ref/alter_table.sgml
View file @ a294726b
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.76 2005/01/10 00:04:43 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.77 2005/01/14 01:16:52 tgl Exp $
PostgreSQL documentation
-->
......@@ -537,6 +537,17 @@ ALTER TABLE distributors
</programlisting>
</para>
<para>
To change an integer column containing UNIX timestamps to <type>timestamp
with time zone</type> via a <literal>USING</literal> clause:
<programlisting>
ALTER TABLE foo
ALTER COLUMN foo_timestamp TYPE timestamp with time zone
USING
timestamp with time zone 'epoch' + foo_timestamp * interval '1 second';
</programlisting>
</para>
<para>
To rename an existing column:
<programlisting>
......
doc/src/sgml/ref/create_opclass.sgml
View file @ a294726b
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_opclass.sgml,v 1.12 2003/11/29 19:51:38 pgsql Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/create_opclass.sgml,v 1.13 2005/01/14 01:16:52 tgl Exp $
PostgreSQL documentation
-->
......@@ -205,6 +205,16 @@ CREATE OPERATOR CLASS <replaceable class="parameter">name</replaceable> [ DEFAUL
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
The operators should not be defined by SQL functions. A SQL function
is likely to be inlined into the calling query, which will prevent
the optimizer from recognizing that the query matches an index.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
......
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