我正在嘗試獲取與第二列中的值匹配的值。例如，我想通過僅使用 ID 來了解比爾·蓋茨的發件人是誰。
我有兩張桌子，
*users* table
| user_ID | Full_name |
| -------- | -------------- |
| 1 | Steve Jobs |
| 2 | Bill Gates |
| 3 | Elon Musk |
*relationships* table (with both column foreign keys)
| user_sender | user_receiver |
| ------------ | -------------- |
| 1 | 2 |
| 3 | 1 |
| 3 | 2 |
我想根據“user_receiver”列選擇“user_sender”列中的匹配值
例如，我想知道 2 OUTPUT 的 user_sender 是誰：
| | |
| ------------ | -------------- |
| 1 | 2 |
| 3 | 2 |
uj5u.com熱心網友回復：
您需要加入表格并選擇您想要的行
您可以通過使用別名來訪問兩個表的所有列
SELECT u.user_ID , u.Full_name,r.user_receiver
FROM users u JOIN
relationships r ON u.user_ID = r.user_sender
WHERE r.user_receiver = 2
uj5u.com熱心網友回復：
如果要根據名稱查找，則將關系加入到用戶中。
SELECT
rel.user_sender
, rel.user_receiver
-- , sender.Full_name AS sender_name
-- , receiver.Full_name AS receiver_name
FROM relationships AS rel
JOIN users AS sender ON sender.user_ID = rel.user_sender
JOIN users As receiver ON receiver.user_ID = rel.user_receiver
WHERE receiver.Full_name = 'Bill Gates'
如果您已經知道 user_receiver 號碼，并且您只想要 ID
SELECT *
FROM relationships
WHERE user_receiver = 2
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