SQL：只選擇一行具有相同值的表

Question

我對 sql 有點陌生，對於我的項目，我需要做一些數據庫排序和過濾：

假設我的數據庫如下所示：

==========================================
|  id       |       email        | name
==========================================
|   1       |  123@test.com      | John
|   2       |  234@test.com      | Peter
|   3       |  234@test.com      | Steward
|   4       |  123@test.com      | Ethan
|   5       |  542@test.com      | Bob
|   6       |  123@test.com      | Patrick
==========================================

我該怎么做才能只返回具有相同電子郵件的最后一列 te 返回：

==========================================
|  id       |       email        | name
==========================================
|   3       |  234@test.com      | Steward
|   5       |  542@test.com      | Bob
|   6       |  123@test.com      | Patrick
==========================================

提前致謝！

Answer 1

SQL查詢：

    SELECT * FROM test.test1  WHERE id IN (
  SELECT MAX(id) FROM test.test1 GROUP BY email
);

希望這能解決您的問題。 謝謝。

Answer 2

在 SQL 中執行此操作的通用方法是使用 ANSI 標准row_number()函數：

select t.*
from (select t.*, row_number() over (partition by email order by id desc) as seqnum
      from t
     ) t
where seqnum = 1;

Answer 3

這是一個更清晰的方法：

SELECT *
FROM table
ORDER BY email DESC
LIMIT 1;

Answer 4

您可以使用以下查詢來獲取每email的MAX id值：

SELECT email, MAX(id)
FROM mytable
GROUP BY email

使用上面的查詢作為派生表，您可以獲得整個記錄：

SELECT t1.*
FROM mytable AS t1
JOIN (
  SELECT email, MAX(id) AS id
  FROM mytable
  GROUP BY email 
) AS t2 ON t1.id = t2.id