mysql使用group_by

佚名 6年前 (2019-04-17) 随笔 1828人围观抢沙发百度已收录

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

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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;