Re: [HACKERS] EXISTS optimization

Kevin Grittner wrote:
> Management has simply given a mandate that the software be independent
> of OS and database vendor, and to use Java to help with the OS independence.
> ... we write all of our queries in ANSI SQL in our own query tool, parse it,
> and generate Java classes to run it.

A better solution, and one I've used for years, is to use OS- or database-specific features, but carefully encapsulate
themin a single module, for example, "database_specific.java". 

For example, when I started supporting both Oracle and Postgres, I encountered the MAX() problem, which (at the time)
wasvery slow in Postgres, but could be replaced by "select X from MYTABLE order by X desc limit 1".  So I created a
function,"GetColumnMax()" that encapsulates the database-specific code for this.  Similar functions encapsulate and a
numberof other database-specific optimizations. 

Another excellent example: I have a function called "TableExists(name)".  To the best of my knowledge, there simply is
noANSI SQL for this, so what do you do?  Encapsulate it in one place. 

The result?  When I port to a new system, I know exactly where to find all of the non-ANSI SQL.  I started this habit
yearsago with C/C++ code, which has the same problem: System calls are not consistent across the varients of Unix,
Windows,and other OS's.  So you put them all in one file called "machine_dependent.c". 

Remember the old adage: There is no such thing as portable code, only code that has been ported.

Cheers,
Craig