mysql使用group_by

GROUP BY必须得配合聚合函数来用，分组之后你可以计数（COUNT），求和（SUM），求平均数（AVG）等

常用聚合函数

• count() 计数
• sum() 求和
• avg() 平均数
• max() 最大值
• min() 最小值

语法：

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name;

如：

-- 抽奖次数
SELECT
	user.`name` AS user_name,
	count(*) AS lottery_count,
	location.`name` AS location_name,
	user_id
FROM
	space_turntable_log
LEFT JOIN user ON user.id = space_turntable_log.user_id
LEFT JOIN location ON location.id = user.location_id
GROUP BY
	user_id;

HAVING

当然提到GROUP BY 我们就不得不提到HAVING，HAVING相当于条件筛选，但它与WHERE筛选不同，HAVING是对于GROUP BY对象进行筛选。　　

-- 抽奖次数
SELECT
user.`name` AS user_name,
count(*) AS lottery_count,
location.`name` AS location_name,
user_id
FROM
space_turntable_log
LEFT JOIN user ON user.id = space_turntable_log.user_id
LEFT JOIN location ON location.id = user.location_id
GROUP BY
user_id HAVING lottery_count>2;

SELECT
yx_user. NAME AS 用户名,
count('*') AS 发布总条数,
yx_location. NAME AS 城市
FROM
yx_space_podcast
LEFT JOIN yx_user ON yx_user.id = yx_space_podcast.user_id
LEFT JOIN yx_location ON yx_user.location_id = yx_location.id
WHERE
yx_space_podcast.created_at > UNIX_TIMESTAMP('2019-04-01 00:00:00')
AND yx_space_podcast.created_at < UNIX_TIMESTAMP('2019-04-27 00:00:00')
AND yx_space_podcast.is_delete = 0
GROUP BY
yx_space_podcast.user_id
HAVING
发布总条数 > 1