Leetcode SQL 50 -- 1517. Find Users With Valid E-Mails

Question

Table name: ``

Column Name	Type
user_id	int
name	varchar
mail	varchar

This table contains information of the users signed up in a website. Some e-mails are invalid.

A valid e-mail has a prefix name and a domain.

domain: @leetcode.com.
prefix name is a string that may contain:

• letters (upper or lower case)
• digits
• underscore _
• period .
• dash -

(The prefix name must start with a letter.)

Write a solution to find the users who have valid emails.
Return the result table in any order.

Explaination

For string validation, there is a powerful tool for pattern matching called RegEx.

In SQL, it provides the keyword REGEXP to enter your pattern for validation.
Here, we simply explain the patterns we used to match the requirement.

Pattern	Meaning
^	Match Beginning of string
$	Match The End of string
[a-zA-Z]	Match any upper and lower case letter
[a-zA-Z0-9_.-]	Match any upper and lower case letter, digits, underscore, period, dash
*	Zero or more instances of string preceding it

Therefore, ^[a-zA-Z][a-zA-Z0-9_.-]* means:

Begins the string with any upper or lower case letter,
follows by zero or more upper and lower case letter, digits, underscore, period, and/or dash.

Solution

SELECT * FROM Users
WHERE mail REGEXP '^[a-zA-Z][a-zA-Z0-9_.-]*@leetcode\\.com$'

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More SQL 50 questions: here