PL/pgSQL RETURNS TABLE 例子

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=#