選擇一個表或數組一個更大的選擇查詢

假設中的每一行，我們有兩個表：

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

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

那裏是一個（項目）很多（消息）的關係。我想在一個查詢中選擇所有的東西，以將其轉換爲java。是否可以寫這樣的查詢，它會給我喜歡輸出：

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

而MESSAGE列是一個數組或類似的東西（不是一個連接字符串）？

來源

2010-12-22 Infeligo

爲什麼你不想每個ID使用多行？一旦你脫離關係模型就很難回頭了，最終你會支持各種奇怪的查詢，這些查詢在很多情況下都是無用的。 – 2010-12-22 14:24:47

@jonearles：查詢如何破壞模型？ – Quassnoi 2010-12-23 11:43:04

爲了鞏固Quassnoi的答案，還有的COLLECT功能，會做同樣的事情，MULTISET在其他回答但沒有子查詢。

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;

來源

2010-12-22 14:38:33

注意：這會給你一個字符串（不是你想要的），但由於這個問題是問經常我會離開這裏，這個答案並沒有所有的人都知道這種簡單的解決方案

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

如果你需要的信息加上括號IDS列出你可以使用串聯：

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

來源

2010-12-22 12:54:57 zerkms

這將導致連接字符串 – Quassnoi 2010-12-22 13:01:40

您可以使用字段級光標：

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

或創建一個表型和投值的MULTISET該類型：

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

來源

2010-12-22 12:57:18 Quassnoi

選擇一個表或數組一個更大的選擇查詢

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