(disclaimer : I don't use postgre. Your code fails appropriately when translated to sybase)
two things stand out from the DBD::PG changelog. 
0.4   Jun 24, 1997
        - adapted to DBI-0.84:
          o new syntax for DBI->connect !
          o execute returns 0E0 -> n for     SELECT stmt
                                  -1 for non SELECT stmt
                                  -2 on error

0.81 June 13, 1998
	- bug-fix from Rolf Grossmann <grossman@securitas.net>:
	  undefined parameters in an execute statement will be 
	  translated from 'undef' to 'NULL'. Also every parameter 
	  for bind_param() will be quoted by default (escape quote 
	  and backslash). Appropriate tests have been added to test.pl.
The first seems to indicate that a failed exec will not die as may be expected with RaiseError, but rather return an error code, and the second may indicate a behavior where nonexistent params are automatically translated into null, although this might be a peculiar interpretation of this note.
Perhaps contacting the module maintainer is in order.

In reply to Re: DBI execute is not failing when placeholder values are not supplied (boo) by boo_radley
in thread DBI execute is not failing when placeholder values are not supplied by princepawn

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