From a302b8e150e3d92a563ae6977bf6f0859ed0994c Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Wed, 31 Mar 2004 16:20:53 +0000 Subject: [PATCH] Back out tutorial changes: --------------------------------------------------------------------------- 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. 2. Some formatting changes to the datetime discussion, as well as addition of a citation of a relevant book on calendars. Christopher Browne --- doc/src/sgml/advanced.sgml | 183 +------------------------------------ doc/src/sgml/datetime.sgml | 57 ++++++------ 2 files changed, 29 insertions(+), 211 deletions(-) diff --git a/doc/src/sgml/advanced.sgml b/doc/src/sgml/advanced.sgml index becc8720bca..6980dc47752 100644 --- a/doc/src/sgml/advanced.sgml +++ b/doc/src/sgml/advanced.sgml @@ -1,5 +1,5 @@ @@ -65,25 +65,11 @@ SELECT * FROM myview; 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. + Building views upon other views is not uncommon. - - - Views differ from real tables in that they are - not, by default, updatable. If they join together several tables, - it may be troublesome to update certain columns since the - real update that must take place requires - identifying the relevant rows in the source tables. This is - discussed further in . - - + Foreign Keys @@ -401,169 +387,6 @@ SELECT name, altitude - - Stored Procedures - - - stored procedures - - - 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 - basic loadable procedural language for - PostgreSQL is . - Numerous other languages may also be used, including , , and . - - - There are several ways that stored procedures are really - helpful: - - - - To centralize data validation code into the - database - - Your system may use client software written in several - languages, perhaps with a web application - implemented in PHP, a server application implemented - in Java, and a report writer 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. - - 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. - - - - Reducing round trips between client and server - - - 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. - - - 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. - - To simplify queries. - - 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 select domain, tld(domain) - from domains; instead of having to put verbose code - using substr() into each query. - - - It is particularly convenient to use scripting languages - like Perl, Tcl, and Python to grovel through strings - since they are designed for text processing. - - The binding to the R statistical language allows - implementing complex statistical queries inside the database, - instead of having to draw the data out. - - - Increasing the level of abstraction - - 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 only allowed access to - stored procedures to update data, and cannot do direct updates to - tables. - - - - - - - - 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. - - 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. - - - - - Triggers - - - triggers - - - Triggers allow running a function either before or after - update (INSERT, DELETE, - UPDATE) operations, which can allow you to do - some very clever things. - - - - Data Validation - - Instead of explicitly coding validation checks as part of a - stored procedure, they may be introduced as BEFORE - triggers. The trigger function checks the input values, raising an - exception if it finds invalid input. - - Note that this is how foreign key checks are implemented in - PostgreSQL; when you define a foreign - key, you will see a message similar to the following: - -NOTICE: CREATE TABLE will create implicit trigger(s) for FOREIGN KEY check(s) - - - In some cases, it may be appropriate for a trigger function - to insert data in order to make the input valid. For - instance, if a newly created object needs a status code in a status - table, the trigger might automatically do that. - - - Audit logs - - One may use AFTER triggers to monitor updates to - vital tables, and INSERT entries into log tables to - provide a more permanent record of those updates. - - - Replication - - The RServ replication system uses - AFTER triggers to track which rows have changed on the - master system and therefore need to be copied over to - slave systems. - - - CREATE TRIGGER "_rserv_trigger_t_" AFTER INSERT OR DELETE OR UPDATE ON "my_table" - FOR EACH ROW EXECUTE PROCEDURE "_rserv_log_" ('10'); - - - - - - Notice that there are strong parallels between what can be - accomplished using triggers and stored procedures, particularly in - regards to data validation. - - Conclusion diff --git a/doc/src/sgml/datetime.sgml b/doc/src/sgml/datetime.sgml index 026fb5d553f..dd5d371e19d 100644 --- a/doc/src/sgml/datetime.sgml +++ b/doc/src/sgml/datetime.sgml @@ -1,5 +1,5 @@ @@ -11,8 +11,8 @@ $PostgreSQL: pgsql/doc/src/sgml/datetime.sgml,v 2.40 2004/03/30 21:58:20 momjian 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, + value, ignored, or rejected. + The parser contains internal lookup tables for all textual fields, including months, days of the week, and time zones. @@ -1056,21 +1056,21 @@ $PostgreSQL: pgsql/doc/src/sgml/datetime.sgml,v 2.40 2004/03/30 21:58:20 momjian years. - 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 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. + 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 cal - program produce the following: + This is why Unix systems have the cal program + produce the following: $ cal 9 1752 @@ -1094,24 +1094,19 @@ $ cal 9 1752 - Different calendars have been developed in various parts of - the world, many predating the Gregorian system. + + 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. + 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. + The People's Republic of China uses the Gregorian calendar + for civil purposes. The Chinese calendar is used for determining + festivals. - - If you are interested in this sort of thing, - Calendrical Calculations: The Millennium Edition 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. -