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SELECT c.CustomerId, CompanyName
from Customers c
WHERE EXISTS(
SELECT OrderID from Orders o
WHERE o.CustomerID = cu.CustomerID)
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USE Northwind
GO
SELECT CategoryName
from Categories
WHERE EXISTS (SELECT NULL)
ORDER BY CategoryName ASC
GO
B. ±È½ÏʹÓà EXISTS ºÍ IN µÄ²éѯ
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USE pubs
GO
SELECT DISTINCT pub_name
from publishers
WHERE EXISTS
    (SELECT *
    from titles
    WHERE pub_id = publishers.pub_id
    AND type = \'business\')
GO
-- Or, using the IN clause:
USE pubs
GO
SELECT distinct pub_name
from publishers
WHERE pub_id IN
    (SELECT pub_id
    from titles
    WHERE type = \'business\')
GO
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