为较大的选择查询的每一行选择一个表或数组

Question

使用Oracle 11g

假设我们有两个表:

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

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

哪里有一个(项目)到多个(消息)的关系.我想在单个查询中选择所有内容以将其转换为java.有可能写这样的查询,它会给我输出像:

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

MESSAGE列是一个数组或类似的东西(不是连接字符串)？

Answer 1

您可以使用字段级游标:

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

或者创建一个表类型并将MULTISET值转换为该类型:

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