mysql生成日期的辅助表

为了解决mysql按日期分组查询统计的时候，没有数据补0。可以生成连续的时间表格来辅助查询
* 生成按天的数据

* 每一个小时为一个分段 生成如下辅助表


*代码如下

CREATE TABLE num ( i INT );
-- 创建一个表用来储存0-9的数字
INSERT INTO num ( i )
VALUES
    ( 0 ),
    ( 1 ),
    ( 2 ),
    ( 3 ),
    ( 4 ),
    ( 5 ),
    ( 6 ),
    ( 7 ),
    ( 8 ),
    ( 9 );
    
-- --------------------------------------------------------------

CREATE TABLE
IF
    NOT EXISTS calendar ( datelist date, datehour datetime );
    
-- --------------------------------------------------------------
INSERT INTO calendar ( datelist ) SELECT -- 生成按天的数据
adddate( ( -- 这里的起始日期,你可以换成当前日期
DATE_FORMAT( "2018-11-10", '%Y-%m-%d' ) ), numlist.id ) AS `date` 
FROM
    (
SELECT
    n1.i + n10.i * 10 + n100.i * 100 + n1000.i * 1000+ n10000.i * 10000 AS id 
FROM
    num n1
    CROSS JOIN num AS n10
    CROSS JOIN num AS n100
    CROSS JOIN num AS n1000
    CROSS JOIN num AS n10000 
    ) AS numlist;
    
-- --------------------------------------------------------------
INSERT INTO calendar ( datehour ) SELECT -- 生成按小时的数据
DATE_ADD( ( DATE_FORMAT( "2018-11-10", '%Y-%m-%d' ) ), INTERVAL numlist.id HOUR ) AS `date` 
FROM
    (
SELECT
    n1.i + n10.i * 10 + n100.i * 100 + n1000.i * 1000+ n10000.i * 10000 AS id 
FROM
    num n1
    CROSS JOIN num AS n10
    CROSS JOIN num AS n100
    CROSS JOIN num AS n1000
    CROSS JOIN num AS n10000 
    ) AS numlist;

 * 按天查询

SELECT
    date( datelist ) datas,
    count( * ) - 1 AS counts 
FROM
    (
SELECT
    datelist 
FROM
    calendar 
WHERE
    ( '2018-11-17' <= date( datelist ) ) 
    AND ( date( datelist ) <= '2018-11-19' ) UNION ALL
SELECT
    createtime 
FROM
    snap_face
    LEFT JOIN device ON snap_face.deviceID = device.id 
WHERE
    ( '2018-11-17' <= date( snap_face.createtime ) ) 
    AND ( date( snap_face.createtime ) <= '2018-11-19' ) 
    ) temp 
GROUP BY
    datas 
ORDER BY
    datas;

* 按小时查询

SELECT
    DATE_FORMAT(datehour,'%Y-%m-%d %H') datas,
    count( * ) - 1 AS counts 
FROM
    (
SELECT
DATE_FORMAT(datehour,'%Y-%m-%d %H') datehour
FROM
    calendar 
WHERE
    ( '2018-11-17' <= date( datehour ) ) 
    AND ( date( datehour ) <= '2018-11-19' ) UNION ALL
SELECT
DATE_FORMAT(createtime,'%Y-%m-%d %H') 
FROM
    snap_face
    LEFT JOIN device ON snap_face.deviceID = device.id 
WHERE
    ( '2018-11-17' <= date( snap_face.createtime ) ) 
    AND ( date( snap_face.createtime ) <= '2018-11-19' ) 
    ) temp 
GROUP BY
    datas 
ORDER BY
    datas;