在SQL中追加查询无法正常工作

Question

INSERT INTO 表2（Customer，Order_Date，Stamp_Date，Travelled_Distance，Units，Country，Comments）

选择

'CustomerFamily' As Customer, 
T1.Order_Date AS Order_Date, 
T1.Stamp_Date AS Stamp_Date, 
T1.Travelled_Distance-T2.Travelled_Distance AS Travelled_Distance, 
T1.Units AS Units, 
'Canada' AS Country, 
'' AS Comments

FROM

Table1 AS T1, 
Table1 AS T2

WHERE

T1.Customer='Jake' And 
T2.Customer='Mike' And 
T2.Order_Date=T1.Order_Date

ORDER BY

T1.Order_Date;

这是我的附加查询，其中有一个计算（对于jake和mike在同一天旅行的日子，它减去了来自jakes的mikes旅行距离）

问题是它完成所有计算并将其放入表2中，但每行计算有两行相同。

为什么重复两次？我无法发现错误

Answer 1

尝试

SELECT DISTINCT 'CustomerFamily' As Customer, 
T1.Order_Date AS Order_Date, 
T1.Stamp_Date AS Stamp_Date, 
T1.Travelled_Distance-T2.Travelled_Distance AS Travelled_Distance, 
T1.Units AS Units, 
'Canada' AS Country, 
'' AS Comments