If duplication is ruled out, the landlord will check the manual for distinguishing keywords upstairs with detailed information.

If you want to find duplicates, you need a subquery. Let's do the experiment with the sample database Northwind.

Select * From Orders Where Exists(Select * From Orders AS Temp Where Temp。 OrderID & lt& gt order. Order number and provisional order. CustomerID = order. CustomerID)

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Select * From table Where Exists(Select * From table AS Temp Where Temp。 unique identification

You must have a unique identifier. If not, you can build one temporarily. This method is not recommended for a large number of data.