「SQL面试题库」 No_119 Find Users With Valid E-Mails

今日真题

题目介绍： Find Users With Valid E-Mails find-users-with-valid-e-mails

难度简单

SQL架构

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. ```

考察正则表达式的使用

sql
SELECT *
FROM Users
WHERE mail REGEXP '^[a-zA-Z]+[\\w_\\.\\-]*@leetcode.com$'   
ORDER BY user_id;

sql
select * from Users
where mail regexp '^[a-zA-Z]+[a-zA-Z0-9_\\./\\-]{0,}@leetcode.com$'
order by user_id

坑点： 1、前缀可能是一个字母，比如“J@leetcode.com”，所以匹配非首字母外的前缀字符数量要用{0,}或*，不能用+。 2、题意要求：underscore '', period '.' and/or dash '-'，/没加单引号，不留神可能写漏/。 3、后缀可能是“@leetcodeecom”，所以要对“.”加转义符号。 4、后缀可能是“@LEETCODE.COM”，默认是不区分大小写匹配，所以要加上“BINARY”区分大小写。 语法： 1、https://www.cnblogs.com/timssd/p/5882742.html 2、https://www.cnblogs.com/zhaopanpan/p/10133224.html 3、"双反斜杠+w"表示字母、数字、下划线，相对"a-zA-Z0-9"的写法更简洁。

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