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需求：使用sql进行分组，然后查询出各自分组内的最新一条记录

表结构：

实现：

SELECT
	business_flag,
	channel_code,
	rate
FROM
	(
		SELECT
			business_flag,
			channel_code,
			max(create_time) AS create_time_2
		FROM
			test 
		WHERE
			toDate (create_time) = '2021-07-01'
		GROUP BY
			business_flag,
			channel_code
	) a
LEFT JOIN test b ON a.business_flag = b.business_flag
AND a.channel_code = b.channel_code
AND a.create_time_2 = b.create_time

思路：先对原数据进行分组去重，得到最新记录，然后依据这个结果，再获取这条记录的其他信息。