题目
Table: Users
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| user_id | int |
| name | varchar |
| mail | varchar |
+---------------+---------+
user_id is the primary key for this table.
This table contains information of the users signed up in a website. Some e-mails are invalid.
Write an SQL query to find the users who have valid emails.
A valid e-mail has a prefix name and a domain where:
The prefix name is a string that may contain letters (upper or lower case), digits, underscore '_', period '.' and/or dash '-'.
The prefix name must start with a letter.
The domain is '@leetcode.com'.
Return the result table in any order.
The query result format is in the following example.
Users
+---------+-----------+-------------------------+
| user_id | name | mail |
+---------+-----------+-------------------------+
| 1 | Winston | winston@leetcode.com |
| 2 | Jonathan | jonathanisgreat |
| 3 | Annabelle | bella-@leetcode.com |
| 4 | Sally | sally.come@leetcode.com |
| 5 | Marwan | quarz#2020@leetcode.com |
| 6 | David | david69@gmail.com |
| 7 | Shapiro | .shapo@leetcode.com |
+---------+-----------+-------------------------+
Result table:
+---------+-----------+-------------------------+
| user_id | name | mail |
+---------+-----------+-------------------------+
| 1 | Winston | winston@leetcode.com |
| 3 | Annabelle | bella-@leetcode.com |
| 4 | Sally | sally.come@leetcode.com |
+---------+-----------+-------------------------+
The mail of user 2 doesn't have a domain.
The mail of user 5 has # sign which is not allowed.
The mail of user 6 doesn't have leetcode domain.
The mail of user 7 starts with a period.
解答
这个就是在考察正则表达式吧
要求
前缀名称是一个字符串，可能包含字母（大写或小写），数字，下划线“ _”，句点. 和/或破折号-。
前缀名称必须以字母开头。
域是“ @ leetcode.com”。
^ 表示开头
$ 表示以什么为结尾
+匹配一个或多个,不包括空
[] 表示集合里的任意一个
\ 用于转义特殊字符
a{m,n} 匹配m到n个a，左侧不写为0，右侧不写为任意
.与_需要转义
select * from Users
where mail regexp '^[a-zA-Z]+[a-zA-Z0-9_\\./\\-]{0,}@leetcode\\.com$'
order by user_id
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