1.編寫一個 SQL 查詢，查找所有至少連續出現三次的數字。

+----+-----+

| Id | Num |

+----+-----+

| 1 | 1 |

| 2 | 1 |

| 3 | 1 |

| 4 | 2 |

| 5 | 1 |

| 6 | 2 |

| 7 | 2 |

+----+-----+

例如，給定上面的?Logs?表，?1?是唯一連續出現至少三次的數字。

+-----------------+

| ConsecutiveNums |

+-----------------+

| 1 |

+-----------------+

select Num as ConsecutiveNums from Logs where Id in(select distinct l1.Id fromLogs l1,Logs l2,Logs l3where (l1.Num = l2.Num and l2.Num =l3.Num and (

(l1.Id+ 1= l2.Id and l2.Id +1 =l3.Id)or

(l3.Id+ 1= l2.Id and l2.Id +1 =l1.Id)or

(l3.Id+ 1= l1.Id and l1.Id +1 =l2.Id)

)

)

order by l1.Id) group by Num

2.編寫一個 SQL 查詢，查找?Person?表中所有重復的電子郵箱。

示例：

+----+---------+

| Id | Email |

+----+---------+

| 1 | a@b.com |

| 2 | c@d.com |

| 3 | a@b.com |

+----+---------+

根據以上輸入，你的查詢應返回以下結果：

+---------+

| Email |

+---------+

| a@b.com |

+---------+

select Email from Person group by Email having count(Email)>1

3.編寫一個 SQL 查詢，來刪除?Person?表中所有重復的電子郵箱，重復的郵箱里只保留?Id?最小的那個。

+----+------------------+

| Id | Email |

+----+------------------+

| 1 | john@example.com |

| 2 | bob@example.com |

| 3 | john@example.com |

+----+------------------+

Id 是這個表的主鍵

delete p1 from Person p1,Person p2 where p1.Email=p2.Email and p1.Id>p2.Id

總結

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