in操作
描述：查询指定城市中的客户
查询句法：
        var in操作 = from c in ctx.Customers
                    where new string[] { "Brandenburg", "Cowes", "Stavern" }.Contains(c.City)
                    select c;

对应SQL：
SELECT [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax]
FROM [dbo].[Customers] AS [t0]
WHERE [t0].[City] IN (@p0, @p1, @p2)
-- @p0: Input String (Size = 11; Prec = 0; Scale = 0) [Brandenburg]
-- @p1: Input String (Size = 5; Prec = 0; Scale = 0) [Cowes]
-- @p2: Input String (Size = 7; Prec = 0; Scale = 0) [Stavern]