一步一步学Linq to sql（四）：查询句法
[2] 一步一步学Linq to sql（四）：查询句法
[3] 一步一步学Linq to sql（四）：查询句法
[4] 一步一步学Linq to sql（四）：查询句法
[5] 一步一步学Linq to sql（四）：查询句法
[6] 一步一步学Linq to sql（四）：查询句法
系列文章导航：
一步一步学Linq to sql（二）：DataContext与实体
distinct
描述：查询顾客覆盖的国家
查询句法：
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var 过滤相同项 = (from c in ctx.Customers orderby c.Country select c.Country).Distinct(); |
对应SQL：
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SELECT DISTINCT [t0].[Country] FROM [dbo].[Customers] AS [t0] |
union
描述：查询城市是A打头和城市包含A的顾客并按照顾客名字排序
查询句法：
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var 连接并且过滤相同项 = (from c in ctx.Customers where c.City.Contains("A") select c).Union (from c in ctx.Customers where c.ContactName.StartsWith("A") select c).OrderBy(c => c.ContactName); |
对应SQL：
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SELECT [t3].[CustomerID], [t3].[CompanyName], [t3].[ContactName], [t3].[ContactTitle], [t3].[Address], [t3].[City], [t3].[Region], [t3].[PostalCode], [t3].[Country], [t3].[Phone], [t3].[Fax] FROM ( SELECT [t2].[CustomerID], [t2].[CompanyName], [t2].[ContactName], [t2].[ContactTitle], [t2].[Address], [t2].[City], [t2].[Region], [t2].[PostalCode], [t2].[Country], [t2].[Phone], [t2].[Fax] FROM ( 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] LIKE @p0 UNION SELECT [t1].[CustomerID], [t1].[CompanyName], [t1].[ContactName], [t1].[ContactTitle], [t1].[Address], [t1].[City], [t1].[Region], [t1].[PostalCode], [t1].[Country], [t1].[Phone], [t1].[Fax] FROM [dbo].[Customers] AS [t1] WHERE [t1].[ContactName] LIKE @p1 ) AS [t2] ) AS [t3] ORDER BY [t3].[ContactName] -- @p0: Input String (Size = 3; Prec = 0; Scale = 0) [%A%] -- @p1: Input String (Size = 2; Prec = 0; Scale = 0) [A%] |
concat
描述：查询城市是A打头和城市包含A的顾客并按照顾客名字排序，相同的顾客信息不会过滤
查询句法：
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var 连接并且不过滤相同项 = (from c in ctx.Customers where c.City.Contains("A") select c).Concat (from c in ctx.Customers where c.ContactName.StartsWith("A") select c).OrderBy(c => c.ContactName); |
对应SQL：
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SELECT [t3].[CustomerID], [t3].[CompanyName], [t3].[ContactName], [t3].[ContactTitle], [t3].[Address], [t3].[City], [t3].[Region], [t3].[PostalCode], [t3].[Country], [t3].[Phone], [t3].[Fax] FROM ( SELECT [t2].[CustomerID], [t2].[CompanyName], [t2].[ContactName], [t2].[ContactTitle], [t2].[Address], [t2].[City], [t2].[Region], [t2].[PostalCode], [t2].[Country], [t2].[Phone], [t2].[Fax] FROM ( 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] LIKE @p0 UNION ALL SELECT [t1].[CustomerID], [t1].[CompanyName], [t1].[ContactName], [t1].[ContactTitle], [t1].[Address], [t1].[City], [t1].[Region], [t1].[PostalCode], [t1].[Country], [t1].[Phone], [t1].[Fax] FROM [dbo].[Customers] AS [t1] WHERE [t1].[ContactName] LIKE @p1 ) AS [t2] ) AS [t3] ORDER BY [t3].[ContactName] -- @p0: Input String (Size = 3; Prec = 0; Scale = 0) [%A%] -- @p1: Input String (Size = 2; Prec = 0; Scale = 0) [A%] |