Question

我想在一个键上将多个结果集连接到1个结果。

有3个表（我在这里只添加相关记录）：

Project table : | id | project |

File table    : | id | project_id |

Approved table: | file_id | dep1_date | dep2_date | dep3_date |

部门默认是日期字符串：0000-00-00 00:00:00 第一个查询是：

SELECT project.project, 
SEC_TO_TIME(AVG(TIME_TO_SEC(TIMEDIFF(approved.dep1_date,file.uploaded_datetime)))) as dep1_avg
FROM APPROVED
LEFT JOIN file on file.id = approved.file_id
LEFT JOIN project on project.id=file.project_id
WHERE approved.dep1_date != '0000-00-00 00:00:00'
GROUP BY project.project

它会给我平均分组的批准时间等项目：

Project    Dep1_avg
project1   01:03:02
project2   04:14:03
project3   00:07:56
...

我想用dep2和dep3_date再次运行此查询2次，并附加到第一个结果集，但包含不同的WHERE statament（approved.dep2_date，approved.dep3_date）。

如何查看表格？

Project    Dep1_avg Dep2_avg Dep3_avg
project1   01:03:02          04:23:11
project2   04:14:03 11:33:44
project3   00:07:56 00:13:43 32:24:17
...

另外2个结果与第一个查询（通过项目）相同，如果没有对某个项目的批准，则Dep2或Dep3将其分为NULL或空

查询的内容是什么？

由于

Answer 1

您不应该使用多个where语句，而是选择是否在select本身内的AVG中包含一行。（通过执行多个子查询，可以完成多个where语句，但这可能效率不高。

SELECT project.project, 
SEC_TO_TIME(AVG(IF( approved.dep1_date != '0000-00-00 00:00:00', TIME_TO_SEC(TIMEDIFF(approved.dep1_date,file.uploaded_datetime), NULL))) as dep1_avg
SEC_TO_TIME(AVG(IF( approved.dep2_date != '0000-00-00 00:00:00', TIME_TO_SEC(TIMEDIFF(approved.dep2_date,file.uploaded_datetime), NULL))) as dep2_avg
SEC_TO_TIME(AVG(IF( approved.dep3_date != '0000-00-00 00:00:00', TIME_TO_SEC(TIMEDIFF(approved.dep3_date,file.uploaded_datetime), NULL))) as dep3_avg
FROM APPROVED
LEFT JOIN file on file.id = approved.file_id
LEFT JOIN project on project.id=file.project_id
GROUP BY project.project

为NULL的值不包含在diff中，因此这基本上只是检查是否应该包含该值，并且在这种情况下将其交换为NULL，这将被忽略。这使您可以废弃整个WHERE子句。

Answer 2

试试这个：

SELECT project.project, 
       SEC_TO_TIME(AVG(TIME_TO_SEC(IF(approved.dep1_date != '0000-00-00 00:00:00', TIMEDIFF(a.dep1_date, f.uploaded_datetime), NULL)))) AS dep1_avg, 
       SEC_TO_TIME(AVG(TIME_TO_SEC(IF(approved.dep2_date != '0000-00-00 00:00:00', TIMEDIFF(a.dep2_date, f.uploaded_datetime), NULL)))) AS dep2_avg, 
       SEC_TO_TIME(AVG(TIME_TO_SEC(IF(approved.dep3_date != '0000-00-00 00:00:00', TIMEDIFF(a.dep3_date, f.uploaded_datetime), NULL)))) AS dep3_avg
FROM APPROVED a
LEFT JOIN `file` f ON f.id = a.file_id
LEFT JOIN project p ON p.id = f.project_id
GROUP BY p.project;

MySQL将多个查询结果连接到1个结果集

2 个答案: