What is the most common domain for the email address among all the customers?
most common domain for the email refers to Max(Count(SUBSTR(email, CHARINDEX('@', email) + 1, length(email) - charindex('@', email))))
SELECT SUBSTR(email, INSTR(email, '@') + 1, LENGTH(email) - INSTR(email, '@')) AS ym FROM customer GROUP BY SUBSTR(email, INSTR(email, '@') + 1, LENGTH(email) - INSTR(email, '@')) ORDER BY COUNT(*) DESC LIMIT 1