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Update CREATE FUNCTION docs: mention use of AS clause with

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INTERNAL functions, add a warning about trying to overload function names
for dynamically loaded C functions (from old man page).
This commit is contained in:
Tom Lane 1999-05-20 02:57:15 +00:00
parent e68abfbeff
commit c9f8ab6fba
1 changed files with 34 additions and 4 deletions
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38
doc/src/sgml/ref/create_function.sgml
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@ -20,7 +20,7 @@
<SYNOPSIS>
CREATE FUNCTION <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">ftype</replaceable> [, ...] ] )
RETURNS <replaceable class="parameter">rtype</replaceable>
AS <replaceable class="parameter">path</replaceable>
AS <replaceable class="parameter">definition</replaceable>
LANGUAGE '<replaceable class="parameter">langname</replaceable>'
</SYNOPSIS>
@ -65,12 +65,13 @@ CREATE FUNCTION <replaceable class="parameter">name</replaceable> ( [ <replaceab
</VARLISTENTRY>
<VARLISTENTRY>
<TERM>
<replaceable class="parameter">path</replaceable>
<replaceable class="parameter">definition</replaceable>
</TERM>
<LISTITEM>
<PARA>
May be either an SQL-query or an absolute path to an
object file.
A string defining the function; the meaning depends on the language.
It may be an internal function name, the path to an object file,
an SQL query, or text in a procedural language.
</PARA>
</LISTITEM>
</VARLISTENTRY>
@ -149,6 +150,35 @@ in the <citetitle>PostgreSQL Programmer's Guide</citetitle>
Use <command>DROP FUNCTION</command>
to drop user-defined functions.
</PARA>
<PARA>
<productname>Postgres</productname> allows function "overloading";
that is, the same name can be used for several different functions
so long as they have distinct argument types. This facility must be
used with caution for INTERNAL and C-language functions, however.
</PARA>
<PARA>
Two INTERNAL functions cannot have the same C name without causing
errors at link time. To get around that, give them different C names
(for example, use the argument types as part of the C names), then
specify those names in the AS clause of <command>CREATE FUNCTION</command>.
If the AS clause is left empty then <command>CREATE FUNCTION</command>
assumes the C name of the function is the same as the SQL name.
</PARA>
<PARA>
For dynamically-loaded C functions, the SQL name of the function must
be the same as the C function name, because the AS clause is used to
give the path name of the object file containing the C code. In this
situation it is best not to try to overload SQL function names. It
might work to load a C function that has the same C name as an internal
function or another dynamically-loaded function --- or it might not.
On some platforms the dynamic loader may botch the load in interesting
ways if there is a conflict of C function names. So, even if it works
for you today, you might regret overloading names later when you try
to run the code somewhere else.
</PARA>
</REFSECT2>
</refsect1>