[英]Oracle SQL to join / union 2 tables and group / sort by ID to create facebook-like timeline
對於一部分課程,我必須創建一個類似Facebook的應用程序。
目前,我正在“時間軸”頁面上工作,並努力應對所需的SQL查詢的復雜性。
我期望的結果是在單個表格和組或排序中顯示帖子和回復,以便回復位於相應帖子的下方
eg post_id text
1 First post
1 Response 1 to post 1
1 Response 2 to post 1
2 Second post
2 Response 1 to post 2
2 Response 2 to post 2
數據庫架構如下:
create or replace type post_obj as object (
post_id number,
post_text varchar2(500),
user_posted_by ref user_obj,
post_date timestamp,
map member function get_postid return number) not final;
create table post_obj_tbl of post_obj;
create or replace type response_obj as object (
response_id number,
response_text varchar2(500),
post_details ref post_obj,
user_posted_by ref user_obj,
response_date timestamp,
map member function get_responseid return number) not final;
create table response_obj_tbl of response_obj;
到目前為止,我設法將兩個表連接在一起,以便獲得一個顯示帖子和回復的表,但該表會自動按用戶ID進行分組。 這是查詢:
SELECT p_tbl.user_posted_by.username, p_tbl.post_text, p_tbl.post_date
FROM post_obj_tbl p_tbl
WHERE
p_tbl.user_posted_by.user_id = (
SELECT u_tbl.user_id
FROM user_obj_tbl u_tbl
WHERE u_tbl.username = (select V('APP_USER') from DUAL) )
OR
p_tbl.user_posted_by.user_id in (
SELECT f_tbl.friend_id
FROM friends_obj_tbl f_tbl
WHERE f_tbl.user_id = (
SELECT u_tbl.user_id
FROM user_obj_tbl u_tbl
WHERE u_tbl.username = (select V('APP_USER') from DUAL) )
)
UNION
SELECT r_tbl.user_posted_by.username, r_tbl.response_text, r_tbl.response_date
FROM response_obj_tbl r_tbl, post_obj_tbl p_tbl
WHERE r_tbl.post_details.post_id = p_tbl.post_id;
我真的希望這是有道理的...我的頭很亂! 任何幫助表示贊賞:)
首先,為什么要創建對象表? 通常的方法是創建這樣的表:
create table post_obj (
post_id number,
post_text varchar2(500),
user_posted_by number,
post_date timestamp);
使用此類表要容易得多,尤其是在APEX中。
關於查詢。 我將參與其中:
SELECT p_tbl.user_posted_by.username, p_tbl.post_text, p_tbl.post_date
FROM post_obj_tbl p_tbl
WHERE
p_tbl.user_posted_by.user_id = (
SELECT u_tbl.user_id
FROM user_obj_tbl u_tbl
WHERE u_tbl.username = (select V('APP_USER') from DUAL) )
可以將其轉換為:
SELECT p_tbl.user_posted_by.username, p_tbl.post_text, p_tbl.post_date
FROM post_obj_tbl p_tbl,
user_obj_tbl u_tbl
WHERE p_tbl.user_posted_by = u_tbl.user_id
AND u_tbl.username = V('APP_USER')
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