Peter Eisentraut wrote:
> Am Dienstag, 30. Dezember 2003 03:01 schrieb Christopher Browne:
> > 1. In keeping with the recent discussion that there should be more
> > said about views, stored procedures, and triggers, in the tutorial, I
> > have added a bit of verbiage to that end.
>
> The idea that seems to get lost here is that the Tutorial is supposed to be
> something for people to try out, not just a list of interesting ideas to keep
> in mind for later on.
>
> > 2. Some formatting changes to the datetime discussion,
>
> Please revert them.
>
> > as well as
> > addition of a citation of a relevant book on calendars.
>
> Citations go into the bibliography.
OK, entire patch reverted. Does someone want to rework this information
to fit into our docs more cleanly?
--
Bruce Momjian | http://candle.pha.pa.us
[EMAIL PROTECTED] | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
Index: doc/src/sgml/advanced.sgml
===================================================================
RCS file: /cvsroot/pgsql-server/doc/src/sgml/advanced.sgml,v
retrieving revision 1.38
retrieving revision 1.40
diff -c -c -r1.38 -r1.40
*** doc/src/sgml/advanced.sgml 29 Nov 2003 19:51:36 -0000 1.38
--- doc/src/sgml/advanced.sgml 30 Mar 2004 22:08:50 -0000 1.40
***************
*** 1,5 ****
<!--
! $PostgreSQL: pgsql-server/doc/src/sgml/advanced.sgml,v 1.38 2003/11/29 19:51:36
pgsql Exp $
-->
<chapter id="tutorial-advanced">
--- 1,5 ----
<!--
! $PostgreSQL: pgsql-server/doc/src/sgml/advanced.sgml,v 1.40 2004/03/30 22:08:50
momjian Exp $
-->
<chapter id="tutorial-advanced">
***************
*** 65,74 ****
<para>
Views can be used in almost any place a real table can be used.
! Building views upon other views is not uncommon.
</para>
- </sect1>
<sect1 id="tutorial-fk">
<title>Foreign Keys</title>
--- 65,88 ----
<para>
Views can be used in almost any place a real table can be used.
! Building views upon other views is not uncommon. You may cut down
! on the difficulty of building complex queries by constructing them
! in smaller, easier-to-verify pieces, using views. Views may be
! used to reveal specific table columns to users that legitimately
! need access to some of the data, but who shouldn't be able to look
! at the whole table.
</para>
+ <para>
+ Views differ from <quote> real tables </quote> in that they are
+ not, by default, updatable. If they join together several tables,
+ it may be troublesome to update certain columns since the
+ <emphasis>real</emphasis> update that must take place requires
+ identifying the relevant rows in the source tables. This is
+ discussed further in <xref linkend="rules-views-update">.
+ </para>
+
+ </sect1>
<sect1 id="tutorial-fk">
<title>Foreign Keys</title>
***************
*** 387,392 ****
--- 401,569 ----
</para>
</sect1>
+ <sect1 id="tutorial-storedprocs">
+ <title> Stored Procedures </title>
+
+ <indexterm zone="tutorial-storedprocs">
+ <primary>stored procedures</primary>
+ </indexterm>
+
+ <para> Stored procedures are code that runs inside the database
+ system. Numerous languages may be used to implement functions and
+ procedures; most built-in code is implemented in C. The
+ <quote>basic</quote> loadable procedural language for
+ <productname>PostgreSQL</productname> is <xref linkend="plpgsql">.
+ Numerous other languages may also be used, including <xref
+ linkend="plperl">, <xref linkend="pltcl">, and <xref
+ linkend="plpython">.
+ </para>
+
+ <para> There are several ways that stored procedures are really
+ helpful:
+
+ <itemizedlist>
+
+ <listitem><para> To centralize data validation code into the
+ database </para>
+
+ <para> Your system may use client software written in several
+ languages, perhaps with a <quote>web application</quote>
+ implemented in PHP, a <quote>server application</quote> implemented
+ in Java, and a <quote> report writer</quote> implemented in Perl.
+ In the absence of stored procedures, you will likely find that data
+ validation code must be implemented multiple times, in multiple
+ languages, once for each application.</para>
+
+ <para> By implementing data validation in stored procedures,
+ running in the database, it can behave uniformly for all these
+ systems, and you do not need to worry about synchronizing
+ validation procedures across the languages.</para>
+
+ </listitem>
+
+ <listitem><para> Reducing round trips between client and server
+ </para>
+
+ <para>A stored procedure may submit multiple queries, looking up
+ information and adding in links to additional tables. This takes
+ place without requiring that the client submit multiple queries,
+ and without requiring any added network traffic.
+ </para>
+
+ <para> As a matter of course, the queries share a single
+ transaction context, and there may also be savings in the
+ evaluation of query plans, that will be similar between invocations
+ of a given stored procedure. </para></listitem>
+
+ <listitem><para> To simplify queries. </para>
+
+ <para> For instance, if you are commonly checking the TLD on domain
+ names, you might create a stored procedure for this purpose, and so
+ be able to use queries such as <command> select domain, tld(domain)
+ from domains; </command> instead of having to put verbose code
+ using <function>substr()</function> into each query.
+ </para>
+
+ <para> It is particularly convenient to use scripting languages
+ like Perl, Tcl, and Python to <quote>grovel through strings</quote>
+ since they are designed for <quote>text processing.</quote></para>
+
+ <para> The binding to the R statistical language allows
+ implementing complex statistical queries inside the database,
+ instead of having to draw the data out.
+ </listitem>
+
+ <listitem><para> Increasing the level of abstraction</para>
+
+ <para> If data is accessed exclusively through stored procedures,
+ then the structures of tables may be changed without there needing
+ to be any visible change in the API used by programmers. In some
+ systems, users are <emphasis>only</emphasis> allowed access to
+ stored procedures to update data, and cannot do direct updates to
+ tables.
+ </para>
+
+ </listitem>
+
+ </itemizedlist>
+ </para>
+
+ <para> These benefits build on one another: careful use of stored
+ procedures can simultaneously improve reliability and performance,
+ whilst simplifying database access code and improving portability
+ across client platforms and languages. For instance, consider that
+ a stored procedure can cheaply query tables in the database to
+ validate the correctness of data provided as input. </para>
+
+ <para> Instead of requiring a whole series of queries to create an
+ object, and to look up parent/subsidiary objects to link it to, a
+ stored procedure can do all of this efficiently in the database
+ server, improving performance, and eliminating whole classes of
+ errors. </para>
+
+ </sect1>
+
+ <sect1 id="tutorial-triggers">
+ <title> Triggers </title>
+
+ <indexterm zone="tutorial-triggers">
+ <primary>triggers</primary>
+ </indexterm>
+
+ <para> Triggers allow running a function either before or after
+ update (<command>INSERT</command>, <command>DELETE</command>,
+ <command>UPDATE</command>) operations, which can allow you to do
+ some very clever things. </para>
+
+ <itemizedlist>
+
+ <listitem><para> Data Validation </para>
+
+ <para> Instead of explicitly coding validation checks as part of a
+ stored procedure, they may be introduced as <command>BEFORE</command>
+ triggers. The trigger function checks the input values, raising an
+ exception if it finds invalid input.</para>
+
+ <para> Note that this is how foreign key checks are implemented in
+ <productname>PostgreSQL</productname>; when you define a foreign
+ key, you will see a message similar to the following:
+ <screen>
+ NOTICE: CREATE TABLE will create implicit trigger(s) for FOREIGN KEY check(s)
+ </screen></para>
+
+ <para> In some cases, it may be appropriate for a trigger function
+ to insert data in order to <emphasis>make</emphasis> the input valid. For
+ instance, if a newly created object needs a status code in a status
+ table, the trigger might automatically do that.</para>
+ </listitem>
+
+ <listitem><para> Audit logs </para>
+
+ <para> One may use <command>AFTER</command> triggers to monitor updates to
+ vital tables, and <command>INSERT</command> entries into log tables to
+ provide a more permanent record of those updates. </para>
+ </listitem>
+
+ <listitem><para> Replication </para>
+
+ <para> The <application>RServ</application> replication system uses
+ <command>AFTER</command> triggers to track which rows have changed on the
+ <quote>master</quote> system and therefore need to be copied over to
+ <quote>slave</quote> systems.</para>
+
+ <para> <command>
+ CREATE TRIGGER "_rserv_trigger_t_" AFTER INSERT OR DELETE OR UPDATE ON
"my_table"
+ FOR EACH ROW EXECUTE PROCEDURE "_rserv_log_" ('10');
+ </command></para>
+ </listitem>
+
+ </itemizedlist>
+
+ <para> Notice that there are strong parallels between what can be
+ accomplished using triggers and stored procedures, particularly in
+ regards to data validation. </para>
+
+ </sect1>
<sect1 id="tutorial-conclusion">
<title>Conclusion</title>
Index: doc/src/sgml/datetime.sgml
===================================================================
RCS file: /cvsroot/pgsql-server/doc/src/sgml/datetime.sgml,v
retrieving revision 2.39
retrieving revision 2.40
diff -c -c -r2.39 -r2.40
*** doc/src/sgml/datetime.sgml 1 Dec 2003 20:34:53 -0000 2.39
--- doc/src/sgml/datetime.sgml 30 Mar 2004 21:58:20 -0000 2.40
***************
*** 1,5 ****
<!--
! $PostgreSQL: pgsql-server/doc/src/sgml/datetime.sgml,v 2.39 2003/12/01 20:34:53 tgl
Exp $
-->
<appendix id="datetime-appendix">
--- 1,5 ----
<!--
! $PostgreSQL: pgsql-server/doc/src/sgml/datetime.sgml,v 2.40 2004/03/30 21:58:20
momjian Exp $
-->
<appendix id="datetime-appendix">
***************
*** 11,18 ****
strings, and are broken up into distinct fields with a preliminary
determination of what kind of information may be in the
field. Each field is interpreted and either assigned a numeric
! value, ignored, or rejected.
! The parser contains internal lookup tables for all textual fields,
including months, days of the week, and time
zones.
</para>
--- 11,18 ----
strings, and are broken up into distinct fields with a preliminary
determination of what kind of information may be in the
field. Each field is interpreted and either assigned a numeric
! value, ignored, or rejected.</para>
! <para> The parser contains internal lookup tables for all textual fields,
including months, days of the week, and time
zones.
</para>
***************
*** 1056,1076 ****
years.
</para>
! <para>
! The papal bull of February 1582 decreed that 10 days should be dropped
! from October 1582 so that 15 October should follow immediately after
! 4 October.
! This was observed in Italy, Poland, Portugal, and Spain. Other Catholic
! countries followed shortly after, but Protestant countries were
! reluctant to change, and the Greek orthodox countries didn't change
! until the start of the 20th century.
!
! The reform was observed by Great Britain and Dominions (including what is
! now the USA) in 1752.
! Thus 2 September 1752 was followed by 14 September 1752.
! This is why Unix systems have the <command>cal</command> program
! produce the following:
<screen>
$ <userinput>cal 9 1752</userinput>
--- 1056,1076 ----
years.
</para>
! <para> The papal bull of February 1582 decreed that 10 days should
! be dropped from October 1582 so that 15 October should follow
! immediately after 4 October.</para>
!
! <para> This was observed in Italy, Poland, Portugal, and Spain.
! Other Catholic countries followed shortly after, but Protestant
! countries were reluctant to change, and the Greek orthodox countries
! didn't change until the start of the 20th century.</para>
!
! <para> The reform was observed by Great Britain and Dominions
! (including what is now the USA) in 1752. Thus 2 September 1752 was
! followed by 14 September 1752.</para>
! <para> This is why Unix systems have the <command>cal</command>
! program produce the following:
<screen>
$ <userinput>cal 9 1752</userinput>
***************
*** 1094,1112 ****
</para>
</note>
! <para>
! Different calendars have been developed in various parts of the
! world, many predating the Gregorian system.
! For example,
! the beginnings of the Chinese calendar can be traced back to the 14th
! century BC. Legend has it that the Emperor Huangdi invented the
! calendar in 2637 BC.
! The People's Republic of China uses the Gregorian calendar
! for civil purposes. The Chinese calendar is used for determining
! festivals.
</para>
</sect1>
</appendix>
--- 1094,1117 ----
</para>
</note>
! <para> Different calendars have been developed in various parts of
! the world, many predating the Gregorian system.</para>
! <para> For example, the beginnings of the Chinese calendar can be
! traced back to the 14th century BC. Legend has it that the Emperor
! Huangdi invented the calendar in 2637 BC.</para>
! <para> The People's Republic of China uses the Gregorian calendar
! for civil purposes. The Chinese calendar is used for determining
! festivals.
</para>
+
+ <para> If you are interested in this sort of thing, <citation>
+ Calendrical Calculations: The Millennium Edition </citation> by by
+ Edward M. Reingold and Nachum Dershowitz is an excellent reference,
+ describing some 25 calendars, and providing software for displaying
+ them and converting between them.</para>
+
</sect1>
</appendix>
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