On Wed, 2007-09-26 at 00:02 -0400, Tom Lane wrote:
> Ow Mun Heng <[EMAIL PROTECTED]> writes:
> > Where can I erad more about this new "feature"?
>
> http://developer.postgresql.org/pgdocs/postgres/sql-createfunction.html
>
> http://developer.postgresql.org/pgdocs/postgres/ always has a current
> snapshot of CVS-HEAD documentation...
I read these two items
...
execution_cost
A positive number giving the estimated execution cost for the
function, in units of cpu_operator_cost. If the function returns a set,
this is the cost per returned row. If the cost is not specified, 1 unit
is assumed for C-language and internal functions, and 100 units for
functions in all other languages. Larger values cause the planner to try
to avoid evaluating the function more often than necessary.
result_rows
A positive number giving the estimated number of rows that the
planner should expect the function to return. This is only allowed when
the function is declared to return a set. The default assumption is 1000
rows.
...
[/snip]
---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
