mysql存储过程中的总值

我试图从数据库中获取具有不同日期时间戳的值的总和。我的目标是返回表中该日期的所有值的每天总数。我的存储过程如下所示：

DELIMITER //
DROP PROCEDURE get_reads;
CREATE PROCEDURE get_reads (IN  device varchar (20), IN start_date datetime, IN end_date datetime, IN read_type varchar(8))

BEGIN

    SELECT dr.date_time, sum(dr.device_reading)
    FROM DEVICE_DETAILS dd,
    DEVICE_READING dr
    WHERE dr.device_id = dd.device_id
    AND dd.serial_number = device
    AND dr.date_time BETWEEN start_date AND end_date
    AND dr.reading_type = read_type;



END//

我相信我将不得不使用临时表或其他东西，但无法在网上找到有关我的情况的任何建议。对于每一天，我每半小时有一个值，我希望存储的过程在我传入的日期范围内返回每天的总计值。数据库列看起来是这样的

+-----------+---------------------+--------------+----------------+-------+
| device_id | date_time           | reading_type | device_reading | units |
+-----------+---------------------+--------------+----------------+-------+
| E1        | 2012-11-19 00:29:00 | Profile      |   0.0719131800 | KW    |
| E1        | 2012-11-19 00:59:00 | Profile      |   0.0802306700 | KW    |
| E1        | 2012-11-19 01:29:00 | Profile      |   0.0767434100 | KW    |
| E1        | 2012-11-19 01:59:00 | Profile      |   0.0737920500 | KW    |
| E1        | 2012-11-19 02:29:00 | Profile      |   0.0794256700 | KW    |
| E1        | 2012-11-19 02:59:00 | Profile      |   0.0729868200 | KW    |
| E1        | 2012-11-19 03:29:00 | Profile      |   0.0745970500 | KW    |
| E1        | 2012-11-19 03:59:00 | Profile      |   0.0804993100 | KW    |
| E1        | 2012-11-19 04:29:00 | Profile      |   0.0837193100 | KW    |
| E1        | 2012-11-19 04:59:00 | Profile      |   0.0483004600 | KW    |

使用CAST（日期时间为日期）解决

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你的问题是…？每个值都是按时间段单独返回的，我想要一整天的总数。但是。。。程序不会返回任何内容。他们只是“做事”：-？不奇怪。您忘记了一个

group by

子句。如果还有时间戳，如何按日期分组？

DELIMITER //
DROP PROCEDURE get_reads;
CREATE PROCEDURE get_reads (IN  device varchar (20), IN start_date datetime, IN end_date datetime, IN read_type varchar(8))

    BEGIN

            SELECT dr.date_time, sum(dr.device_reading)
            FROM DEVICE_DETAILS dd,
            DEVICE_READING dr
            WHERE dr.device_id = dd.device_id
            AND dd.serial_number = device
            AND dr.date_time BETWEEN start_date AND end_date
            AND dr.reading_type = read_type
            GROUP BY CAST(dr.date_time AS DATE);



    END//