[英]SQL - joining rows from same table
我只知道最簡單的SQL,所以請把我當成一個完整的菜鳥吧!
我有一個有很多行的表,但有些可以通過id配對,我想要合並這些行的返回數組。
post_id # meta_name # meta_value #
======================================
1 # bar # 44 #
1 # foo # on #
2 # bar # 1 #
2 # foo # on #
3 # bar # 1 #
3 # foo # off #
作為縮小版本,想象一下我的表格,我的目標是返回2個結果
1 # foo # bar # 44 # on
2 # foo # bar # 1 # on
基於ids相關且c2的值為'on'
我的嘗試是從一些閱讀,但沒有得到任何地方的以下
SELECT
t1.post_id, t2.post_id, t1.meta_name, t2.meta_name, t1.meta_value, t2.meta_value
FROM
`ecom_page_meta` t1
JOIN
`ecom_page_meta` t2
ON
t1.post_id = t2.post_id
WHERE
t1.meta_name = 'featured-products'
AND
t1.meta_value = 'on'
任何幫助將非常感激
**編輯**
我想我只是發布了下面的答案得到了很好的語法:
SELECT L.post_id, L.meta_name, R.meta_name, L.meta_value, R.meta_value
FROM `ecom_page_meta` L
INNER JOIN ecom_page_meta R
ON L.post_id = R.post_id
AND L.meta_name = 'featured-products-order'
AND R.meta_value = 'on'
WHERE R.meta_name = 'featured-products'
ORDER BY L.meta_value
DESC
再次感謝。
創建測試數據:
SQL> create table ecom_page_meta (post_id number not null
2 , meta_name varchar2(15) not null
3 , meta_value varchar2(15) not null);
Table created.
SQL> insert into ecom_page_meta values (1, 'bar', '44');
1 row created.
SQL> insert into ecom_page_meta values (1, 'foo', 'on');
1 row created.
SQL> insert into ecom_page_meta values (2, 'bar', '1');
1 row created.
SQL> insert into ecom_page_meta values (2, 'foo', 'on');
1 row created.
SQL> insert into ecom_page_meta values (3, 'bar', '1');
1 row created.
SQL> insert into ecom_page_meta values (3, 'foo', 'off');
1 row created.
SQL> commit;
Commit complete.
查詢以給出匹配OP樣本的結果:
SQL> select L.post_id, L.meta_name, R.meta_name, L.meta_value, R.meta_value
2 from ecom_page_meta L
3 inner join ecom_page_meta R
4 on L.post_id = R.post_id
5 and L.meta_value <> 'on'
6 and R.meta_value = 'on'
7 where L.meta_name = 'bar';
POST_ID META_NAME META_NAME META_VALUE META_VALUE
---------- --------------- --------------- --------------- ---------------
1 bar foo 44 on
2 bar foo 1 on
我仍然不知道什么是WHERE t1.meta_name = 'featured-products'
與任何事情有關,因為沒有樣本數據包括字符串'featured-products'的t1.meta_name。
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