PostgreSQL retrieve records with items in array with array_agg

Question

My database system is PostgreSQL 8.4

The following is the example schema:

CREATE TABLE items(
  item_code varchar(20) NOT NULL PRIMARY KEY,
  item_description varchar(200),
  item_pieces_per_pack integer
);

CREATE TABLE customer_orders (
  order_id integer,
  item_code varchar(20),
  required_shipping_date date,
  quantity integer,
  PRIMARY KEY (order_id ,item_code,required_shipping_date)
);

INSERT INTO items VALUES ('AL0000063','PANETTONE CLASSICO BASSO 1KG',1);
INSERT INTO items VALUES ('AL0000064','PANDORO CLASSICO 1KG',1);
INSERT INTO items VALUES ('AL0000065','TORRONE CIOCCOLATO E NOCCIOLE 250G',4);
INSERT INTO items VALUES ('AL0000066','CANTUCCI TOSCANI 100G',6);
INSERT INTO items VALUES ('AL0000067','SAGRANTINO DI MONTEFALCO',6);
INSERT INTO items VALUES ('AL0000068','BAROLO',6);
INSERT INTO items VALUES ('AL0000069','AMARONE',6);


INSERT INTO customer_orders VALUES (1,'AL0000063','2013-12-15',5);
INSERT INTO customer_orders VALUES (1,'AL0000066','2013-12-15',15);
INSERT INTO customer_orders VALUES (1,'AL0000067','2013-12-14',15);
INSERT INTO customer_orders VALUES (2,'AL0000063','2013-12-11',25);
INSERT INTO customer_orders VALUES (2,'AL0000064','2013-12-11',25);
INSERT INTO customer_orders VALUES (2,'AL0000067','2013-12-13',25);
INSERT INTO customer_orders VALUES (3,'AL0000063','2013-12-13',25);
INSERT INTO customer_orders VALUES (3,'AL0000065','2013-12-10',10);
INSERT INTO customer_orders VALUES (3,'AL0000065','2013-12-20',10);

I need to retrieve from the table "items" only record with item_code in a array. The following query work fine:

SELECT * FROM items
WHERE item_code = ANY('{AL0000063,AL0000064,AL0000065}'::text[])

But when I use a sub query with array_agg:

SELECT * FROM items
WHERE item_code = ANY(
  SELECT array_agg(DISTINCT item_code) 
  FROM customer_orders 
  WHERE required_shipping_date BETWEEN '2013-12-01' AND '2013-12-15')

PostgreSQL raises the error:

ERROR: operator does not exist: character varying = character varying[] LINE 2: WHERE item_code = ANY( ^ HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.

Why?

Answer 1

It must be something with parsing SQL by Postgres, because with extra cast to varchar[] it works fine:

 SELECT * FROM items
WHERE item_code = ANY((
  SELECT array_agg(DISTINCT item_code)
  FROM customer_orders
  WHERE required_shipping_date BETWEEN '2013-12-01' AND '2013-12-15')::varchar[]);

Anyway, there is no need to use array in this case:

SELECT * FROM items
WHERE item_code IN (
  SELECT DISTINCT item_code
  FROM customer_orders
  WHERE required_shipping_date BETWEEN '2013-12-01' AND '2013-12-15');