sqlserver查询数据表中每个类别最新的一条记录

表tariff_info, 原始数据:

想要的结果:以start_time时间倒序排序, 以code分类, 查询每一类最新的一条记录

sql:

SELECT
    a.*
FROM
    TARIFF_INFO a,
    (
        SELECT
            code,
            MAX (start_time) start_time
        FROM
            TARIFF_INFO
        GROUP BY
            code
    ) b
WHERE
    a.start_time = b.start_time
AND a.code = b.code
ORDER BY
    a.code

这样查询结果已经实现了, 但是需要添加过滤条件, 即当前时间在start_time和end_time之间.  如果还用上面的sql仅仅在末尾追加一个条件发现查询结果为空:

所以必须在子查询中添加同样的过滤条件方可查出正确结果, 如下面sql:

SELECT
    a.*
FROM
    TARIFF_INFO a,
    (
        SELECT
            code,
            MAX (start_time) start_time
        FROM
            TARIFF_INFO
        WHERE
            start_time <= '2018-09-18'
        GROUP BY
            code
    ) b
WHERE
    a.start_time = b.start_time
AND a.code = b.code
AND a.start_time <= '2018-09-18'
ORDER BY
    a.code

另:需要注意sql中时间区间的比较<=貌似有临界日期会漏掉的情况, 这里不作赘述了.以下sql和上面的异曲同工:

SELECT
    a.*
FROM
    TARIFF_INFO a
INNER JOIN (
    SELECT
        code,
        MAX (start_time) 'start_time'
    FROM
        TARIFF_INFO
    WHERE CONVERT(VARCHAR(10),start_time,121) <= '2018-09-18'
    GROUP BY
        code
) b ON a.code = b.code
AND a.start_time = b.start_time
AND CONVERT(VARCHAR(10),b.start_time,121) <= '2018-09-18'
ORDER BY
    a.code

感谢:https://blog.csdn.net/sinat_27693393/article/details/78673971