SELECT 
    CASE 
        WHEN LENGTH(phone) = 11 THEN CONCAT(LEFT(phone, 3), '****', RIGHT(phone, 4))
        ELSE 'Invalid Phone'
    END AS masked_phone,
    COUNT(*) AS count
FROM users
GROUP BY masked_phone;

SELECT 
    REGEXP_REPLACE(email, '(.)(.*)(@.+)', '\1****\3') AS masked_email,
    COUNT(*) AS count
FROM customers
GROUP BY masked_email;

CREATE FUNCTION mask_name(name VARCHAR(255))
RETURNS VARCHAR(255)
BEGIN
    RETURN CONCAT(LEFT(name, 1), REPEAT('*', LENGTH(name)-1));
END;

SELECT 
    mask_name(username) AS masked_username,
    COUNT(*) AS user_count
FROM accounts
GROUP BY masked_username;

SELECT 
    CONCAT(LEFT(name, 2), REPEAT('*', LENGTH(name)-2)) AS masked_name,
    SUBSTRING(zip_code, 1, 3) AS partial_zip,
    COUNT(*) AS count
FROM customers
GROUP BY masked_name, partial_zip;

-- 对年龄分组统计
SELECT 
    FLOOR(age/10)*10 AS age_group,
    COUNT(*) AS count
FROM patients
GROUP BY age_group;