BUG #15794: Defects regarding stored procedure parameters

The following bug has been logged on the website:

Bug reference: 15794
Logged by: Dada Zhang
Email address: 740084020(at)qq(dot)com
PostgreSQL version: 10.7
Operating system: windows 10 Home
Description:

( I am not good at English, English is not my native language, please excuse
typing errors. )

When the parameter name of the stored procedure is the same as the table
field name of the update statement, a problem is caused: "field association
is ambiguous."

Such as:

There have a table and some record:
```
CREATE TABLE "public"."student" (
"id" int4 NOT NULL,
"name" varchar(255),
PRIMARY KEY ("id")
);
insert into "public"."student"(id,name) VALUES (1,'Zhang San');
insert into "public"."student"(id,name) VALUES (2,'Li Si');
```

There have a function (it will caused: Field association \"id\" is
ambiguous)
```
CREATE OR REPLACE FUNCTION public.update_student(
id integer,
name character varying)
RETURNS "pg_catalog"."void"
LANGUAGE 'plpgsql'

COST 100
VOLATILE
AS $BODY$
BEGIN
UPDATE public.student SET name = update_student.name
WHERE id = update_student.id;
END;
$BODY$;
```

But, when we change the function: (it will be ok, the sql execute
successed)
```
CREATE OR REPLACE FUNCTION public.update_student(
_id integer,
name character varying)
RETURNS "pg_catalog"."void"
LANGUAGE 'plpgsql'

COST 100
VOLATILE
AS $BODY$
BEGIN
UPDATE public.student SET name = update_student.name
WHERE id = _id;
END;
$BODY$;
```
or
(this function also have a problem, PostgreSQL after 9, SQL string escape is
cumbersome)
```
CREATE OR REPLACE FUNCTION public.update_student(
_id integer,
name character varying)
RETURNS "pg_catalog"."void"
LANGUAGE 'plpgsql'

COST 100
VOLATILE
AS $BODY$
DECLARE
v_sql varchar;
BEGIN
v_sql := 'UPDATE public.student SET name = ' || E'\'' ||
update_student.name || E'\'' ||
' WHERE id = ' || E'\'' || id || E'\'' || ';';
EXECUTE v_sql;
END;
$BODY$;
```

The above. thank you.