For all intents and purposes, PostgreSQL has less of a need for CREATE PROCEDURE than other databases aside from looking more like other databases.
For example in SQL Server -> 2005 - although you can write functions that return tables and so forth, you have to resort to writing
CLR functions marked as unsafe to actually update data in a stored function. This gets pretty messy and has its own limitations so you have no choice but to use a stored procedures, which can not be called from within an SQL query.
In MySQL 5.1 the abilities of functions are even more limiting - they can't even return a dataset.
In PostgreSQL, you can
write a function marked as VOLATILE that updates data and that can do all sorts of wacky things that are useful
but considered by some to be perverse such as the following:
SELECT rule_id, rule_name, fnprocess_rule(rule_id) As process_result
WHERE brules.category = 'Pay Employees'
ORDER BY brules.rule_order
Another thing stored procedures can usually do that functions can not is to return multiple result sets. PostgreSQL can simulate such behavior
by creating a function that returns a set of refcursors. See this .NET example Getting full results in a DataSet object: Using refcursors way down the page,
that demonstrates creating a postgresql function that returns a set of refcursors to return multiple result sets using the Npgsql driver.
Prior to PostgreSQL 8.1, people could yell and scream, but PostgreSQL doesn't support Output Parameters. As weird as it is for a function to support
such a thing, PostgreSQL 8.1+ do support output parameters and ODBC drivers and such can even use the standard CALL interface to grab those values.
At a glance it appears that PostgreSQL functions do all that stored procedures do plus more. So the question is, is there any reason
for PostgreSQL to support bonafide stored procedures aside from the obvious To be more compatible with other databases and not have to answer the philosophical question, But you really don't support stored procedures?.
There must be some efficiency benefits to declaring something as a store procedure and having it called in that way. Not quite sure if anyone has done benchmarks on that.
So for the time being PostgreSQL functions have the uncanny role of having a beak like a duck and the flexibility of a beaver, but having the makeup of a Platypus.
In later issues we'll be covering other PostgreSQL contribs. We would like to start our first issue with introducing, PostGIS, one of our favorite PostgreSQL contribs. PostGIS spatially enables PostgreSQL in an OpenGeospatial Consortium (OGC) compliant way.
PostGIS was one reason we started using PostgreSQL way back in 2001 when Refractions
released the first version of PostGIS with the objective of providing affordable basic OGC Compliant spatial functionality to rival the very expensive commercial offerings.
There is perhaps nothing more powerful in the geospatial world than the succinct expressiveness of SQL married with spatial operators and functions.
Together they allow you to manipulate and analyze space with a single sentence. For details on using Postgis and why you would want to, check out the following links
Just as PostgreSQL has grown over the years, so too has PostGIS and the whole FOSS4G ecosystem. PostGIS has benefited from both the FOSS4G and PostgreSQL growths. On the PostgreSQL, improvements such as improved GIST indexing, bitmap indexes etc and on the FOSS4G side dependency projects such as
Geos and Proj4, and JTS, as well as more tools and applications being built on top of it.
In terms of spatial databases, PostGIS is the most capable open source spatial database extender.
While MySQL does have some spatial capabilities, its spatial capabilities are extremely limited particularly in the selectivity of the spatial relational functions
which are all MBR only, ability to create spatial indexes on non-MyISAM stores, and lack a lot of the OGC compliant functions such as Intersection, Buffering even in its 5.1 product. For details on this check the
MySQL 5.1 docs - Spatial Extensions.
When compared with commercial spatial databases, PostGIS has most of the core functions you will see in the commercial databases such as Oracle Spatial, DB2 Spatial Blade, Informix Spatial Blade, has comparable speed, fewer deployment headaches, but lacks some of the advanced add-ons you will find, such as Oracle Spatial network topology model, Raster Support and Geodetic support. Often times the advanced spatial features are add-ons on top of the standard price of the database software.
Some will argue that for example Oracle provides Locator free of charge in their standard and XE versions,
Oracle Locator has a limited set of spatial functions.
Oracle's Locator is missing most of the core spatial analysis and geometric manipulation functions like centroid, buffering, intersection and spatial aggregate functions; granted it does sport geodetic functionality that PostGIS is currently lacking. To use those non-locator features requires Oracle Spatial and Oracle Enterprise which would cost upwards of $60,000 per processor. Many have heard of SQL Server 2008 coming out and the new spatial features it will sport which will be available in both the express and the full version. One feature that SQL Server 2008 will have that PostGIS currently lacks is Geodetic support (the round world model so to speak). Aside from that SQL Server 2008 has a glarying omission from a current GIS perspective - and that is the ability to transform from one spatial reference system to another directly in the database and is Windows bound so not an option for anyone who needs or is thinking of cross-platform or in a Unix environment.
SQL Server 2008 will probably come closest to PostGIS in terms of price / functionality.
The express versions of the commercial offerings have many limitations in terms of size of database and
usually limited to one processor use. For any reasonably sized deployment in terms of database size, processor utilization, replication, or ISP/Service Provider/Integrator this is not adequate and for any reasonably large deployment that is not receiving manna from heaven, some of the commercial offerings like Oracle Spatial, are not cost-sensible.
There is a rise in the use of mapping and geospatial analysis in the world and it is moving out of its GIS comfort zone to mingle more with other IT Infrastructure, General Sciences, and Engineering. Mapping and the whole Geospatial industry is not just a tool for GIS specialists anymore.
A lot of this rise is driven by the rise of mapping mashups - things like Google Maps, Microsoft Virtual Earth, and Open data initiatives that are introducing new avenues of map sharing and spatial awareness.
This new rise is what many refer to as NeoGeography. NeoGeography is still in its infancy; people are just getting over the excitement of seeing dots in their hometown, and are quickly moving into the next level
- where more detailed questions are being asked about those dots and dots are no longer sufficient. We want to draw trails such as trail of hurricane destruction, avian bird flu, track our movement with GPS, draw boundaries and measure the densities of these based on some socio-ecological factor and we need to store all that user generated or tool generated information,
and have all that transactional goodness, security and ability to query in an easy way that a relational database offers. This is the level where PostGIS and other spatial databases are most useful.