为什么这个 Update 查询会添加记录？

Question

我有两个数据库，n 和 p。下面是我正在尝试使用的更新查询。我希望它添加从 n 到 p 的日期和项目编号。出于某种原因，在我 运行 查询之后，我在 p 中得到了更多的记录，然后我开始了。这是怎么回事？

UPDATE DatesAndProjectNumbers

AS n 

LEFT JOIN Projects 

AS p 

ON (n.[Customer Number] = p.[Customer Number]) 

AND (n.[Measure Received] = p.[Measure Received]) 

SET p.PO = [n].[PO], p.[PGI/Invoice] = [n].[PGI/Invoice], p.Cancelled = [n].[Cancelled];

Answer 1

http://blog.sqlauthority.com/2013/04/30/sql-server-update-from-select-statement-using-join-in-update-statement-multiple-tables-in-update-statement/

UPDATE DatesAndProjectNumbers

AS n 

INNER JOIN Projects 

AS p 

ON (n.[Customer Number] = p.[Customer Number]) 

AND (n.[Measure Received] = p.[Measure Received]) 

SET p.PO = [n].[PO], p.[PGI/Invoice] = [n].[PGI/Invoice], p.Cancelled = [n].[Cancelled];