Database: books
Question: What is the most common domain for the email address among all the customers?
SQL: 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