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 **** --- 1,5 ---- *************** *** 65,74 **** Views can be used in almost any place a real table can be used. ! Building views upon other views is not uncommon. - Foreign Keys --- 65,88 ---- 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. + + 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 *************** *** 387,392 **** --- 401,569 ---- + + 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 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 **** --- 1,5 ---- *************** *** 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. --- 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. *************** *** 1056,1076 **** 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 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: $ cal 9 1752 --- 1056,1076 ---- 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 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: $ cal 9 1752 *************** *** 1094,1112 **** ! ! 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. --- 1094,1117 ---- ! 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. + + 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. +