Question

我希望每24小时获得一次转换报告。我有这个查询，但它只返回19个而不是24个任何人都可以告诉我这个错误吗？提前谢谢。

SELECT   HOUR( `date_time` ) AS Hours, COUNT(conversion_id) AS `conversion` FROM conversions 
RIGHT JOIN (SELECT  0 AS Hour 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 UNION ALL SELECT 10 UNION ALL SELECT 11 
    UNION ALL SELECT 12 UNION ALL SELECT 13 UNION ALL SELECT 14 UNION ALL SELECT 15 UNION ALL SELECT 16 UNION ALL SELECT 17 UNION ALL 
    SELECT 18  UNION ALL SELECT 19 UNION ALL SELECT 20 UNION ALL SELECT 21 UNION ALL SELECT 22 UNION ALL SELECT 23) AS AllHours 
ON HOUR(date_time) = Hour 
WHERE DATE(date_time) = CURDATE() OR date_time IS NULL 
GROUP BY Hour 
ORDER BY Hour

Answer 1

如果此时间没有条目，则永远不会选中。你必须反过来查询。

我认为它应该是这样的（没有你的数据库很难测试）：

select * from (SELECT  0 AS Hour 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 UNION ALL SELECT 10 UNION ALL SELECT 11      UNION ALL SELECT 12 UNION ALL SELECT 13 UNION ALL SELECT 14 UNION ALL SELECT 15 UNION ALL SELECT 16 UNION ALL SELECT 17 UNION ALL      SELECT 18  UNION ALL SELECT 19 UNION ALL SELECT 20 UNION ALL SELECT 21 UNION ALL SELECT 22 UNION ALL SELECT 23)   as AllHours
left outer join 
    (select  COUNT(conversion_id) as cnt, HOUR(date_time) as h 
     FROM conversions 
     WHERE DATE(date_time) = CURDATE() OR date_time IS NULL 
     group by h) as c 
on Hour = e.h

Answer 2

right join几乎是正确的。我更喜欢where条件中的on条件（而不是检查NULL个值。但是，关键是使用{{1}中的AllHours表}和select：

group by

Mysql每小时报告查询

2 个答案: