Question

我有一个查询，根据另一个数据库（database2）的结果将数据插入一个数据库（database1）。我担心的是，当我运行此查询时，我将引入一些潜在的重复项。

我的查询工作正常：

Insert into Customers (CustomerID, dateCreated)(
Select CustomerID, datecreated
FROM         Database2.dbo.Customers
Where datecreated between @startdate and @enddate))

现在，我想通过检查CustomerID字段来捕获重复项，如果它已经存在于database1中，则不会插入到database1中。

我想到这样的事情：

Insert into Customers (CustomerID, dateCreated)(
    Select CustomerID, datecreated
    FROM         Database2.dbo.Customers
    Where datecreated between @startdate and @enddate))
Where not exists (Select customerid from customers)

我知道这不太对，但是我被卡住了。

Answer 1

您可以使用左连接完成此操作。检查联接表customerid值是否为null可确保它在源数据库中不存在。

INSERT into Database1.dbo.Customers 
    (CustomerID,
     dateCreated)
SELECT 
     CustomerID, 
     datecreated
FROM Database2.dbo.Customers c2
LEFT JOIN Database1.dbo.Customers c1 ON c1.CustomerID = c2.CustomerID
WHERE c2.datecreated between @startdate and @enddate
  AND c1.CustomerId IS NULL

Answer 2

您可以使用if not exists，它只会扫描表格并查看它是否存在。请注意，它不会读取数据，因此无法进行检查。

IF NOT EXISTS (SELECT TOP 1 1 from Database1.dbo.customers WHERE customerid = 'the id you want to not duplicate')
BEGIN
Insert into Customers (CustomerID, dateCreated)(
Select CustomerID, datecreated
FROM         Database.dbo.Customers
Where datecreated between @startdate and @enddate))
END

如何根据不存在的位置插入

2 个答案: