SELECT DISTINCT UserID, SUBSTRING_INDEX(SUBSTRING_INDEX(Email, ',', num), ',', -1) email
FROM users
JOIN ( SELECT 1 num UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5
UNION SELECT 6 UNION SELECT 7 UNION SELECT 8 UNION SELECT 9 UNION SELECT 10 ) nums
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…