Select a table or array for each row of a larger select query

Question

Using Oracle 11g

Suppose we have two tables:

CREATE TABLE items (
    item_id NUMBER(22,0)
);

CREATE TABLE messages (
    item_id NUMBER(22,0),
    message_code NUMBER(22,0)
);

where there is one (element) for many (messages) relationships. I want to select all materials in one query to get it in java. You can write a query such that it gives me the output:

ID         MESSAGE
----------------------------------
1          (100, 105, 201)
2          (100, 105)

where is the MESSAGE column an ​​array or something like that (not a concatenated row)?

Answer 1

To build Quassnoi's answer, there is a function COLLECTthat will do the same as MULTISETin the other answer, but without a subquery.

CREATE TYPE t_message_code AS TABLE OF INTEGER;

WITH    items AS
        (
        SELECT  1 AS item_id
        FROM    dual
        UNION ALL
        SELECT  2 AS item_id
        FROM    dual
        ),
        messages AS
        (
        SELECT  1 AS item_id, 100 AS message_code
        FROM    dual
        UNION ALL
        SELECT  1 AS item_id, 105 AS message_code
        FROM    dual
        UNION ALL
        SELECT  1 AS item_id, 201 AS message_code
        FROM    dual
        UNION ALL
        SELECT  2 AS item_id, 100 AS message_code
        FROM    dual
        UNION ALL
        SELECT  2 AS item_id, 15 AS message_code
        FROM    dual
        )
SELECT  i.item_id, 
  cast(collect(m.message_code) as t_message_code) as messages_codes
FROM    
  items i
  join messages m on (m.item_id = i.item_id)
group by i.item_id;

Answer 2

You can use field level cursors:

WITH    items AS
        (
        SELECT  1 AS item_id
        FROM    dual
        UNION ALL
        SELECT  2 AS item_id
        FROM    dual
        ),
        messages AS
        (
        SELECT  1 AS item_id, 100 AS message_code
        FROM    dual
        UNION ALL
        SELECT  1 AS item_id, 105 AS message_code
        FROM    dual
        UNION ALL
        SELECT  1 AS item_id, 201 AS message_code
        FROM    dual
        UNION ALL
        SELECT  2 AS item_id, 100 AS message_code
        FROM    dual
        UNION ALL
        SELECT  2 AS item_id, 15 AS message_code
        FROM    dual
        )
SELECT  item_id,
        CURSOR
        (
        SELECT  message_code
        FROM    messages m
        WHERE   m.item_id = i.item_id
        )
FROM    items i

MULTISET :

CREATE TYPE t_message_code AS TABLE OF INTEGER

WITH    items AS
        (
        SELECT  1 AS item_id
        FROM    dual
        UNION ALL
        SELECT  2 AS item_id
        FROM    dual
        ),
        messages AS
        (
        SELECT  1 AS item_id, 100 AS message_code
        FROM    dual
        UNION ALL
        SELECT  1 AS item_id, 105 AS message_code
        FROM    dual
        UNION ALL
        SELECT  1 AS item_id, 201 AS message_code
        FROM    dual
        UNION ALL
        SELECT  2 AS item_id, 100 AS message_code
        FROM    dual
        UNION ALL
        SELECT  2 AS item_id, 15 AS message_code
        FROM    dual
        )
SELECT  item_id,
        CAST
        (
        MULTISET
        (
        SELECT  message_code
        FROM    messages m
        WHERE   m.item_id = i.item_id
        ) AS t_message_code
        )
FROM    items i

Answer 3

NOTE : this will give you a line (not what you wanted), but I will leave this answer here, as this question is asked quite often, and not all people still know about such a simple solution

  SELECT item_id AS id,
         wm_concat(message_code) AS message
    FROM messages
GROUP BY item_id

If you need parentheses around the list of message identifiers, you can use concatenation:

'(' || wm_concat(message_code) || ')' AS message