mysql獲取1000天內的連續時間段.

 select * from (
 
     select a.hours    
                    from (
                            select SUBSTRING('2019-05-06 00:00:00',1,10) - INTERVAL (a.a + (10 * b.a) + (100 * c.a)) DAY as hours
                            from (select 0 as a union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) as a
                            cross join (select 0 as a union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) as b
                            cross join (select 0 as a union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) as c
                    ) a
                    where a.hours between DATE_ADD('2019-05-01 00:00:00',INTERVAL -1 day) and '2019-05-09 00:00:00'; )
                
  原理, 利用sql 得到連續1到1000的自然數, 在利用日期,分別減去這1000個自然數,就是每一天的日期. 

功能: 常用於,多個字段分組, 比如按天.按地區. 無數據,當天補0.  配合前端做圖表展示