My Solution
```
# Write your MySQL query statement below
SELECT
  user_id,
  email
FROM
  Users
WHERE
  -- the email contains exactly one @ symbol
  INSTR(email, '@') <> 0 AND
  -- the email ends with .com
  LOWER(SUBSTR(email, LENGTH(email) - 3, 4)) = '.com' AND
  -- the part before the @ symbol contains only alphanumeric characters and underscores
  REGEXP_LIKE(LOWER(SUBSTR(email, 1, INSTR(email, '@') - 1)), '[a-z_0-9]') AND
  -- the part after the @ symbol and before .com contains a domain name that contains only letters.
  REGEXP_LIKE(LOWER(SUBSTR(email, INSTR(email, '@') + 1, LENGTH(email) - 4 - INSTR(email, '@'))), '[a-z]');

```
['MySQL']