题解 | #分群并计算群体人数#

/* 分群并计算群体人数 */
SELECT
    (
        CASE
            WHEN age < 20 THEN '20以下'
            WHEN age < 50 AND age > 20 THEN '20-50'
            WHEN age > 50 THEN '50以上'
            ELSE '未填写'
        END 
    ) AS age_group,
    COUNT(customer_id) AS user_count
FROM
    customers_info
GROUP BY
    -- 注意：如果要实现分组统计功能，GROUP BY部分要和SELECT部分保持一致
    (
        CASE
            WHEN age < 20 THEN '20以下'
            WHEN age < 50 AND age > 20 THEN '20-50'
            WHEN age > 50 THEN '50以上'
            ELSE '未填写'
        END 
    )
;