LeetCode MySQL-182. Duplicate Emails

    AllenLi
    LeetCode MySQL

    Write an SQL query to report all the duplicate emails.
    Return the result table in any order

    寫一個 SQL Query來報告有重複的信件。
可任意排序結果。

    Table: Person

    +-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| email       | varchar |
+-------------+---------+
id is the primary key column for this table.
Each row of this table contains an email. The emails will not contain uppercase letters.

    Example 1:

    Input: 
Person table:
+----+---------+
| id | email   |
+----+---------+
| 1  | a@b.com |
| 2  | c@d.com |
| 3  | a@b.com |
+----+---------+
Output: 
+---------+
| Email   |
+---------+
| a@b.com |
+---------+
Explanation: a@b.com is repeated two times.

    Solution:
    1. 確認標題 email 為 Email 。
    2. 來自 Person 的 table。
    3. 以 email 為群組。
    4. 有 Email 次數大於1。

    Code.1:

    SELECT email AS Email
  FROM Person
GROUP BY email
HAVING COUNT(Email) > 1;

    Code.2:

    SELECT email AS Email
  FROM Person
GROUP BY email
HAVING COUNT(*) > 1;

    newEmail

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