欢迎投稿

今日深度:

LeetCode——Delete Duplicate Emails(巧用mysql临时表),mysql临时表

LeetCode——Delete Duplicate Emails(巧用mysql临时表),mysql临时表


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  |
+----+------------------+
Note:

Your output is the whole Person?table after executing your sql. Use delete statement.

此题有两个解法:

我初步尝试用以下sql解决问题(要删除的记录Id肯定大于相同内容的Id):

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

但是无法通过,究其原因是在sql语句中,SELECTDELETE操作不能同时存在.

答案一

因此尝试新的解法,直接使用删除语句,结果如下所示:

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

此答案通过测试,但是效率较低.

答案二

后续思考中发现,可以使用临时表解决SELECTDELETE同时存在的问题,答案如下所示:

DELETE FROM Person
WHERE Id IN
(
    SELECT Id FROM
        (SELECT p1.Id as Id FROM Person p1, Person p2 WHERE p1.Email = p2.Email AND p1.Id > p2.Id) AS TEMP
)

此解决方案完美解决问题,且sql语句比较清晰明了.

www.htsjk.Com true http://www.htsjk.com/Mysql/37590.html NewsArticle LeetCode——Delete Duplicate Emails(巧用mysql临时表),mysql临时表 Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id.+----+------------------+|...
相关文章
    暂无相关文章
评论暂时关闭