[SQL]LeetCode196. 删除重复的电子邮箱 | Delete Duplicate Emails

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Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id.

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
Id is the primary key column for this table.

For example, after running your query, the above Person table should have the following rows:

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+

---

编写一个 SQL 查询，来删除 Person 表中所有重复的电子邮箱，重复的邮箱里只保留 Id 最小 的那个。

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
Id 是这个表的主键。

例如，在运行你的查询语句之后，上面的 Person 表应返回以下几行:

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+

---

517ms

DELETE
FROM person
WHERE id NOT IN (SELECT t.id
                 FROM (
                        SELECT min(id) AS id
                        FROM Person
                        GROUP BY email
                      ) t);

---

500ms

# Write your MySQL query statement below
DELETE
FROM Person
WHERE Id IN (
    SELECT Id
    FROM (
        SELECT
        Id, Email, (Email = @prev) AS dup, @prev := Email
        FROM (
            SELECT Email, Id
            FROM Person
            ORDER BY 1, 2
        ) AS sorted,
        (SELECT @prev := NULL) AS init
    ) AS t
    WHERE dup IS TRUE
)

---

505ms

# Write your MySQL query statement below
delete from Person where Id not in(select t.Id from (select min(Id) id from Person b group by Email) t)