实验如下：
RETURNS TABLE 中的变量名和SQL文中的变量名同名时，执行时会出错：
pgsql=# create table sales(itemno integer,quantity integer,price numeric);
CREATE TABLE
pgsql=# insert into sales values (100,15,11.2),(101,22,12.3);
INSERT 0 2
pgsql=# CREATE FUNCTION extended_sales(p_itemno int)
pgsql-# RETURNS TABLE(quantity int, total numeric) AS $$
pgsql$# BEGIN
pgsql$# RETURN QUERY SELECT quantity, quantity * price FROM sales
pgsql$# WHERE itemno = p_itemno;
pgsql$# END;
pgsql$# $$ LANGUAGE plpgsql;
CREATE FUNCTION
pgsql=#
pgsql=# select extended_sales(101);
ERROR: column reference "quantity" is ambiguous
LINE 1: SELECT quantity, quantity * price FROM sales
^
DETAIL: It could refer to either a PL/pgSQL variable or a table column.
QUERY: SELECT quantity, quantity * price FROM sales
WHERE itemno = p_itemno
CONTEXT: PL/pgSQL function "extended_sales" line 2 at RETURN QUERY
pgsql=#
此时，可以如此操作：
pgsql$# RETURN QUERY SELECT sales.quantity, sales.quantity * sales.price FROM sales
pgsql$# WHERE itemno = p_itemno;
pgsql$# END;
pgsql$# $$ LANGUAGE plpgsql;
CREATE FUNCTION
pgsql=#
pgsql=# select extended_sales(101);
extended_sales
----------------
(22,270.6)
(1 row)
pgsql=#
也可以采用别的名称：
pgsql=# CREATE FUNCTION extended_sales(p_itemno int)
pgsql-# RETURNS TABLE(tmp_quantity int, tmp_total numeric) AS $$
pgsql$# BEGIN
pgsql$# RETURN QUERY SELECT quantity AS tmp_quantity, quantity * price AS tmp_total
pgsql$# FROM sales
pgsql$# WHERE itemno = p_itemno;
pgsql$# END;
pgsql$# $$ LANGUAGE plpgsql;
CREATE FUNCTION
pgsql=#
pgsql=# select extended_sales(101);
extended_sales
----------------
(22,270.6)
(1 row)
pgsql=#
