如何取出每天最接近04:00的数据

用created_at减去对应日期4点的差值取绝对值之后，然后按绝对值小到大排序，这个数据量，感觉应该先冗余一个差值绝对值字段 :speak_no_evil:

select * from (SELECT
    *, ABS(
        (
            UNIX_TIMESTAMP(created_at) - UNIX_TIMESTAMP(
                CONCAT(
                    DATE_FORMAT(created_at, "%Y-%m-%d"),
                    " 04:00:00"
                )
            )
        )
    ) AS math_sub,
    DATE_FORMAT(created_at, "%Y-%m-%d") as days
FROM
    table_name
ORDER BY
    math_sub ASC) as b
GROUP BY b.days

SELECT
    * 
FROM
    (
    SELECT
        *,
        row_number() over (
            PARTITION BY market_id,
            date( created_at ) 
        ORDER BY
            ABS(
                UNIX_TIMESTAMP( created_at ) - UNIX_TIMESTAMP(
                CONCAT( DATE_FORMAT( created_at, '%Y-%m-%d' ), ' 04:00:00' ))) 
        ) AS rn 
    FROM
        sentiments 
    WHERE
        created_at >= TIMESTAMP ( '2014-01-01' ) 
        AND created_at < TIMESTAMP ( '2014-02-01' ) 
        AND market_id = 1 
    ) d 
WHERE
    rn = 1

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