This is the "grand finale" that goes on top of the "DROP FUNCTION of
multiple functions" patch set.  The purpose is to allow referring to
functions without having to spell out the argument list, when the
function name is unique.  This is especially useful when having to
operate on "business logic" functions with many many arguments.  It's an
SQL standard feature, and it applies everywhere a function is referred
to in the grammar.  We already have the lookup logic for the regproc
type, and thanks to the grand refactoring of the parser representation
of functions, this is quite a small patch.  There is a bit of
reduce/reduce parser mystery, to keep the reviewer entertained.  (The
equivalent could be implemented for aggregates and operators, but I
haven't done that here yet.)

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
From 40eeb753abc83bbb0e38997fb518f9cd663f1729 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pete...@gmx.net>
Date: Sat, 25 Feb 2017 19:13:15 -0500
Subject: [PATCH] Allow referring to functions without arguments when unique

In DDL commands referring to an existing function, allow omitting the
argument list if the function name is unique in its schema, per SQL
standard.

This uses the same logic that the regproc type uses for finding
functions by name only.
---
 doc/src/sgml/ref/alter_extension.sgml           |  2 +-
 doc/src/sgml/ref/alter_function.sgml            | 13 ++++++------
 doc/src/sgml/ref/alter_opfamily.sgml            |  7 ++++---
 doc/src/sgml/ref/comment.sgml                   |  2 +-
 doc/src/sgml/ref/create_cast.sgml               |  6 ++++--
 doc/src/sgml/ref/create_transform.sgml          | 12 +++++++----
 doc/src/sgml/ref/drop_function.sgml             | 26 ++++++++++++++++++++----
 doc/src/sgml/ref/grant.sgml                     |  2 +-
 doc/src/sgml/ref/revoke.sgml                    |  2 +-
 doc/src/sgml/ref/security_label.sgml            |  2 +-
 src/backend/nodes/copyfuncs.c                   |  1 +
 src/backend/nodes/equalfuncs.c                  |  1 +
 src/backend/parser/gram.y                       | 27 +++++++++++++++++++++++++
 src/backend/parser/parse_func.c                 | 17 +++++++++++++++-
 src/include/nodes/parsenodes.h                  |  3 +++
 src/test/regress/expected/create_function_3.out |  9 ++++++++-
 src/test/regress/sql/create_function_3.sql      |  7 +++++++
 17 files changed, 113 insertions(+), 26 deletions(-)

diff --git a/doc/src/sgml/ref/alter_extension.sgml b/doc/src/sgml/ref/alter_extension.sgml
index de6d6dca16..a7c0927d1c 100644
--- a/doc/src/sgml/ref/alter_extension.sgml
+++ b/doc/src/sgml/ref/alter_extension.sgml
@@ -39,7 +39,7 @@
   EVENT TRIGGER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN DATA WRAPPER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN TABLE <replaceable class="PARAMETER">object_name</replaceable> |
-  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) |
+  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ] |
   MATERIALIZED VIEW <replaceable class="PARAMETER">object_name</replaceable> |
   OPERATOR <replaceable class="PARAMETER">operator_name</replaceable> (<replaceable class="PARAMETER">left_type</replaceable>, <replaceable class="PARAMETER">right_type</replaceable>) |
   OPERATOR CLASS <replaceable class="PARAMETER">object_name</replaceable> USING <replaceable class="parameter">index_method</replaceable> |
diff --git a/doc/src/sgml/ref/alter_function.sgml b/doc/src/sgml/ref/alter_function.sgml
index 0388d06b95..168eeb7c52 100644
--- a/doc/src/sgml/ref/alter_function.sgml
+++ b/doc/src/sgml/ref/alter_function.sgml
@@ -21,15 +21,15 @@
 
  <refsynopsisdiv>
 <synopsis>
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     <replaceable class="PARAMETER">action</replaceable> [ ... ] [ RESTRICT ]
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     RENAME TO <replaceable>new_name</replaceable>
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     OWNER TO { <replaceable>new_owner</replaceable> | CURRENT_USER | SESSION_USER }
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     SET SCHEMA <replaceable>new_schema</replaceable>
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     DEPENDS ON EXTENSION <replaceable>extension_name</replaceable>
 
 <phrase>where <replaceable class="PARAMETER">action</replaceable> is one of:</phrase>
@@ -75,7 +75,8 @@ <title>Parameters</title>
     <term><replaceable class="parameter">name</replaceable></term>
     <listitem>
      <para>
-      The name (optionally schema-qualified) of an existing function.
+      The name (optionally schema-qualified) of an existing function.  If no
+      argument list is specified, the name must be unique in its schema.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/alter_opfamily.sgml b/doc/src/sgml/ref/alter_opfamily.sgml
index 4511c7f7b2..0bafe5b8f8 100644
--- a/doc/src/sgml/ref/alter_opfamily.sgml
+++ b/doc/src/sgml/ref/alter_opfamily.sgml
@@ -25,7 +25,7 @@
   {  OPERATOR <replaceable class="parameter">strategy_number</replaceable> <replaceable class="parameter">operator_name</replaceable> ( <replaceable class="parameter">op_type</replaceable>, <replaceable class="parameter">op_type</replaceable> )
               [ FOR SEARCH | FOR ORDER BY <replaceable class="parameter">sort_family_name</replaceable> ]
    | FUNCTION <replaceable class="parameter">support_number</replaceable> [ ( <replaceable class="parameter">op_type</replaceable> [ , <replaceable class="parameter">op_type</replaceable> ] ) ]
-              <replaceable class="parameter">function_name</replaceable> ( <replaceable class="parameter">argument_type</replaceable> [, ...] )
+              <replaceable class="parameter">function_name</replaceable> [ ( <replaceable class="parameter">argument_type</replaceable> [, ...] ) ]
   } [, ... ]
 
 ALTER OPERATOR FAMILY <replaceable>name</replaceable> USING <replaceable class="parameter">index_method</replaceable> DROP
@@ -195,8 +195,9 @@ <title>Parameters</title>
     <term><replaceable class="parameter">function_name</replaceable></term>
     <listitem>
      <para>
-      The name (optionally schema-qualified) of a function that is an
-      index method support procedure for the operator family.
+      The name (optionally schema-qualified) of a function that is an index
+      method support procedure for the operator family.  If no argument list
+      is specified, the name must be unique in its schema.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/comment.sgml b/doc/src/sgml/ref/comment.sgml
index c1cf587cb2..7483c8c03f 100644
--- a/doc/src/sgml/ref/comment.sgml
+++ b/doc/src/sgml/ref/comment.sgml
@@ -37,7 +37,7 @@
   EVENT TRIGGER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN DATA WRAPPER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN TABLE <replaceable class="PARAMETER">object_name</replaceable> |
-  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) |
+  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ] |
   INDEX <replaceable class="PARAMETER">object_name</replaceable> |
   LARGE OBJECT <replaceable class="PARAMETER">large_object_oid</replaceable> |
   MATERIALIZED VIEW <replaceable class="PARAMETER">object_name</replaceable> |
diff --git a/doc/src/sgml/ref/create_cast.sgml b/doc/src/sgml/ref/create_cast.sgml
index 11266755e5..a7d13edc22 100644
--- a/doc/src/sgml/ref/create_cast.sgml
+++ b/doc/src/sgml/ref/create_cast.sgml
@@ -19,7 +19,7 @@
  <refsynopsisdiv>
 <synopsis>
 CREATE CAST (<replaceable>source_type</replaceable> AS <replaceable>target_type</replaceable>)
-    WITH FUNCTION <replaceable>function_name</replaceable> (<replaceable>argument_type</replaceable> [, ...])
+    WITH FUNCTION <replaceable>function_name</replaceable> [ (<replaceable>argument_type</replaceable> [, ...]) ]
     [ AS ASSIGNMENT | AS IMPLICIT ]
 
 CREATE CAST (<replaceable>source_type</replaceable> AS <replaceable>target_type</replaceable>)
@@ -192,7 +192,7 @@ <title>Parameters</title>
     </varlistentry>
 
     <varlistentry>
-     <term><replaceable>function_name</replaceable>(<replaceable>argument_type</replaceable> [, ...])</term>
+     <term><literal><replaceable>function_name</replaceable>[(<replaceable>argument_type</replaceable> [, ...])]</literal></term>
 
      <listitem>
       <para>
@@ -200,6 +200,8 @@ <title>Parameters</title>
        be schema-qualified.  If it is not, the function will be looked
        up in the schema search path.  The function's result data type must
        match the target type of the cast.   Its arguments are discussed below.
+       If no argument list is specified, the function name must be unique in
+       its schema.
       </para>
      </listitem>
     </varlistentry>
diff --git a/doc/src/sgml/ref/create_transform.sgml b/doc/src/sgml/ref/create_transform.sgml
index f44ee89d33..647c3b9f05 100644
--- a/doc/src/sgml/ref/create_transform.sgml
+++ b/doc/src/sgml/ref/create_transform.sgml
@@ -19,8 +19,8 @@
  <refsynopsisdiv>
 <synopsis>
 CREATE [ OR REPLACE ] TRANSFORM FOR <replaceable>type_name</replaceable> LANGUAGE <replaceable>lang_name</replaceable> (
-    FROM SQL WITH FUNCTION <replaceable>from_sql_function_name</replaceable> (<replaceable>argument_type</replaceable> [, ...]),
-    TO SQL WITH FUNCTION <replaceable>to_sql_function_name</replaceable> (<replaceable>argument_type</replaceable> [, ...])
+    FROM SQL WITH FUNCTION <replaceable>from_sql_function_name</replaceable> [ (<replaceable>argument_type</replaceable> [, ...]) ],
+    TO SQL WITH FUNCTION <replaceable>to_sql_function_name</replaceable> [ (<replaceable>argument_type</replaceable> [, ...]) ]
 );
 </synopsis>
  </refsynopsisdiv>
@@ -104,7 +104,7 @@ <title>Parameters</title>
     </varlistentry>
 
     <varlistentry>
-     <term><replaceable>from_sql_function_name</replaceable>(<replaceable>argument_type</replaceable> [, ...])</term>
+     <term><literal><replaceable>from_sql_function_name</replaceable>[(<replaceable>argument_type</replaceable> [, ...])]</literal></term>
 
      <listitem>
       <para>
@@ -116,12 +116,14 @@ <title>Parameters</title>
        SQL-level function returning <type>internal</type> without at
        least one argument of type <type>internal</type>.)  The actual return
        value will be something specific to the language implementation.
+       If no argument list is specified, the function name must be unique in
+       its schema.
       </para>
      </listitem>
     </varlistentry>
 
     <varlistentry>
-     <term><replaceable>to_sql_function_name</replaceable>(<replaceable>argument_type</replaceable> [, ...])</term>
+     <term><literal><replaceable>to_sql_function_name</replaceable>[(<replaceable>argument_type</replaceable> [, ...])]</literal></term>
 
      <listitem>
       <para>
@@ -130,6 +132,8 @@ <title>Parameters</title>
        <type>internal</type> and return the type that is the type for the
        transform.  The actual argument value will be something specific to the
        language implementation.
+       If no argument list is specified, the function name must be unique in
+       its schema.
       </para>
      </listitem>
     </varlistentry>
diff --git a/doc/src/sgml/ref/drop_function.sgml b/doc/src/sgml/ref/drop_function.sgml
index 5969b084b4..44446e2fac 100644
--- a/doc/src/sgml/ref/drop_function.sgml
+++ b/doc/src/sgml/ref/drop_function.sgml
@@ -21,7 +21,7 @@
 
  <refsynopsisdiv>
 <synopsis>
-DROP FUNCTION [ IF EXISTS ] <replaceable class="parameter">name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) [, ...]
+DROP FUNCTION [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ] [, ...]
     [ CASCADE | RESTRICT ]
 </synopsis>
  </refsynopsisdiv>
@@ -56,7 +56,8 @@ <title>Parameters</title>
     <term><replaceable class="parameter">name</replaceable></term>
     <listitem>
      <para>
-      The name (optionally schema-qualified) of an existing function.
+      The name (optionally schema-qualified) of an existing function.  If no
+      argument list is specified, the name must be unique in its schema.
      </para>
     </listitem>
    </varlistentry>
@@ -141,14 +142,31 @@ <title>Examples</title>
 <programlisting>
 DROP FUNCTION sqrt(integer), sqrt(bigint);
 </programlisting></para>
+
+  <para>
+   If the function name is unique in its schema, it can be referred to without
+   an argument list:
+<programlisting>
+DROP FUNCTION update_employee_salaries;
+</programlisting>
+   Note that this is different from
+<programlisting>
+DROP FUNCTION update_employee_salaries();
+</programlisting>
+   which refers to a function with zero arguments, whereas the first variant
+   can refer to a function with any number of arguments, including zero, as
+   long as the name is unique.
+  </para>
  </refsect1>
 
  <refsect1 id="SQL-DROPFUNCTION-compatibility">
   <title>Compatibility</title>
 
   <para>
-   A <command>DROP FUNCTION</command> statement is defined in the SQL
-   standard, but it is not compatible with this command.
+   This command conforms to the SQL standard, except that the standard only
+   allows one function to be dropped per command, and apart from the
+   <literal>IF EXISTS</> option and the ability to specify argument modes and
+   names, which are all <productname>PostgreSQL</> extension.
   </para>
  </refsect1>
 
diff --git a/doc/src/sgml/ref/grant.sgml b/doc/src/sgml/ref/grant.sgml
index d8ca39f869..9fb4c2fd7e 100644
--- a/doc/src/sgml/ref/grant.sgml
+++ b/doc/src/sgml/ref/grant.sgml
@@ -55,7 +55,7 @@
     TO <replaceable class="PARAMETER">role_specification</replaceable> [, ...] [ WITH GRANT OPTION ]
 
 GRANT { EXECUTE | ALL [ PRIVILEGES ] }
-    ON { FUNCTION <replaceable>function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_type</replaceable> [, ...] ] ) [, ...]
+    ON { FUNCTION <replaceable>function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_type</replaceable> [, ...] ] ) ] [, ...]
          | ALL FUNCTIONS IN SCHEMA <replaceable class="PARAMETER">schema_name</replaceable> [, ...] }
     TO <replaceable class="PARAMETER">role_specification</replaceable> [, ...] [ WITH GRANT OPTION ]
 
diff --git a/doc/src/sgml/ref/revoke.sgml b/doc/src/sgml/ref/revoke.sgml
index fc00129620..ce532543f0 100644
--- a/doc/src/sgml/ref/revoke.sgml
+++ b/doc/src/sgml/ref/revoke.sgml
@@ -70,7 +70,7 @@
 
 REVOKE [ GRANT OPTION FOR ]
     { EXECUTE | ALL [ PRIVILEGES ] }
-    ON { FUNCTION <replaceable>function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_type</replaceable> [, ...] ] ) [, ...]
+    ON { FUNCTION <replaceable>function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_type</replaceable> [, ...] ] ) ] [, ...]
          | ALL FUNCTIONS IN SCHEMA <replaceable>schema_name</replaceable> [, ...] }
     FROM { [ GROUP ] <replaceable class="PARAMETER">role_name</replaceable> | PUBLIC } [, ...]
     [ CASCADE | RESTRICT ]
diff --git a/doc/src/sgml/ref/security_label.sgml b/doc/src/sgml/ref/security_label.sgml
index 998fe3b7c0..afd86aff3a 100644
--- a/doc/src/sgml/ref/security_label.sgml
+++ b/doc/src/sgml/ref/security_label.sgml
@@ -30,7 +30,7 @@
   DOMAIN <replaceable class="PARAMETER">object_name</replaceable> |
   EVENT TRIGGER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN TABLE <replaceable class="PARAMETER">object_name</replaceable>
-  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) |
+  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ] |
   LARGE OBJECT <replaceable class="PARAMETER">large_object_oid</replaceable> |
   MATERIALIZED VIEW <replaceable class="PARAMETER">object_name</replaceable> |
   [ PROCEDURAL ] LANGUAGE <replaceable class="PARAMETER">object_name</replaceable> |
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index bb2a8a3586..3612b9be2f 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -2961,6 +2961,7 @@ _copyObjectWithArgs(const ObjectWithArgs *from)
 
 	COPY_NODE_FIELD(objname);
 	COPY_NODE_FIELD(objargs);
+	COPY_SCALAR_FIELD(args_unspecified);
 
 	return newnode;
 }
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 9fa83b9453..ae6e334ff2 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -1099,6 +1099,7 @@ _equalObjectWithArgs(const ObjectWithArgs *a, const ObjectWithArgs *b)
 {
 	COMPARE_NODE_FIELD(objname);
 	COMPARE_NODE_FIELD(objargs);
+	COMPARE_SCALAR_FIELD(args_unspecified);
 
 	return true;
 }
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index ec07056617..738397bc7c 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -7198,6 +7198,33 @@ function_with_argtypes:
 					n->objargs = extractArgTypes($2);
 					$$ = n;
 				}
+			/*
+			 * Because of reduce/reduce conflicts, we can't use func_name
+			 * below, but we can write it out the long way, which actually
+			 * allows more cases.
+			 */
+			| type_func_name_keyword
+				{
+					ObjectWithArgs *n = makeNode(ObjectWithArgs);
+					n->objname = list_make1(makeString(pstrdup($1)));
+					n->args_unspecified = true;
+					$$ = n;
+				}
+			| ColId
+				{
+					ObjectWithArgs *n = makeNode(ObjectWithArgs);
+					n->objname = list_make1(makeString($1));
+					n->args_unspecified = true;
+					$$ = n;
+				}
+			| ColId indirection
+				{
+					ObjectWithArgs *n = makeNode(ObjectWithArgs);
+					n->objname = check_func_name(lcons(makeString($1), $2),
+												  yyscanner);
+					n->args_unspecified = true;
+					$$ = n;
+				}
 		;
 
 /*
diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index dd9749f205..06bcc99893 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -1914,6 +1914,21 @@ LookupFuncName(List *funcname, int nargs, const Oid *argtypes, bool noError)
 
 	clist = FuncnameGetCandidates(funcname, nargs, NIL, false, false, noError);
 
+	/*
+	 * If no arguments were specified, the name must yield a unique candidate.
+	 */
+	if (nargs == -1 && clist)
+	{
+		if (clist->next)
+			ereport(ERROR,
+					(errcode(ERRCODE_AMBIGUOUS_FUNCTION),
+					 errmsg("function name \"%s\" is not unique",
+							NameListToString(funcname)),
+					 errhint("Specify the argument list to select the function unambiguously.")));
+		else
+			return clist->oid;
+	}
+
 	while (clist)
 	{
 		if (memcmp(argtypes, clist->args, nargs * sizeof(Oid)) == 0)
@@ -1962,7 +1977,7 @@ LookupFuncWithArgs(ObjectWithArgs *func, bool noError)
 		args_item = lnext(args_item);
 	}
 
-	return LookupFuncName(func->objname, argcount, argoids, noError);
+	return LookupFuncName(func->objname, func->args_unspecified ? -1 : argcount, argoids, noError);
 }
 
 /*
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 956f99830c..83e92821a4 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1772,6 +1772,9 @@ typedef struct ObjectWithArgs
 	NodeTag		type;
 	List	   *objname;		/* qualified name of function/operator */
 	List	   *objargs;		/* list of Typename nodes */
+	bool		args_unspecified; /* argument list was omitted, so name must
+								   * be unique (note that objargs == NIL means
+								   * zero args) */
 } ObjectWithArgs;
 
 /*
diff --git a/src/test/regress/expected/create_function_3.out b/src/test/regress/expected/create_function_3.out
index cc4e98a1d4..c85230b93a 100644
--- a/src/test/regress/expected/create_function_3.out
+++ b/src/test/regress/expected/create_function_3.out
@@ -218,13 +218,19 @@ SELECT routine_name, ordinal_position, parameter_name, parameter_default
 (7 rows)
 
 DROP FUNCTION functest_IS_1(int, int, text), functest_IS_2(int), functest_IS_3(int);
+-- overload
+CREATE FUNCTION functest_B_2(bigint) RETURNS bool LANGUAGE 'sql'
+       IMMUTABLE AS 'SELECT $1 > 0';
+DROP FUNCTION functest_b_1;
+DROP FUNCTION functest_b_2;  -- error, ambiguous
+ERROR:  function name "functest_b_2" is not unique
+HINT:  Specify the argument list to select the function unambiguously.
 -- Cleanups
 DROP SCHEMA temp_func_test CASCADE;
 NOTICE:  drop cascades to 16 other objects
 DETAIL:  drop cascades to function functest_a_1(text,date)
 drop cascades to function functest_a_2(text[])
 drop cascades to function functest_a_3()
-drop cascades to function functest_b_1(integer)
 drop cascades to function functest_b_2(integer)
 drop cascades to function functest_b_3(integer)
 drop cascades to function functest_b_4(integer)
@@ -237,5 +243,6 @@ drop cascades to function functext_f_1(integer)
 drop cascades to function functext_f_2(integer)
 drop cascades to function functext_f_3(integer)
 drop cascades to function functext_f_4(integer)
+drop cascades to function functest_b_2(bigint)
 DROP USER regress_unpriv_user;
 RESET search_path;
diff --git a/src/test/regress/sql/create_function_3.sql b/src/test/regress/sql/create_function_3.sql
index 66a463b089..1c0623ba7f 100644
--- a/src/test/regress/sql/create_function_3.sql
+++ b/src/test/regress/sql/create_function_3.sql
@@ -158,6 +158,13 @@ CREATE FUNCTION functest_IS_3(a int default 1, out b int)
 
 DROP FUNCTION functest_IS_1(int, int, text), functest_IS_2(int), functest_IS_3(int);
 
+-- overload
+CREATE FUNCTION functest_B_2(bigint) RETURNS bool LANGUAGE 'sql'
+       IMMUTABLE AS 'SELECT $1 > 0';
+
+DROP FUNCTION functest_b_1;
+DROP FUNCTION functest_b_2;  -- error, ambiguous
+
 
 -- Cleanups
 DROP SCHEMA temp_func_test CASCADE;
-- 
2.12.0

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