Linq to SQL 语法记录....DISTINCT & UNION & CONCAT & 取相交项 & 排除相交项

DISTINCT

描述：查询顾客覆盖的国家

查询句法：

var 过滤相同项 = (from c in ctx.Customers orderby c.Country select c.Country).Distinct();

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：

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);

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：

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);

取项相交
描述：查询城市是A打头的顾客和城市包含A的顾客的交集，并按照顾客名字排序

查询句法：

var 取相交项 = (from c in ctx.Customers where c.City.Contains("A") select c).Intersect

            (from c in ctx.Customers where c.ContactName.StartsWith("A") select c).OrderBy(c => c.ContactName);

排除相交项

描述：查询城市包含A的顾客并从中删除城市以A开头的顾客，并按照顾客名字排序

查询句法：

var 排除相交项 = (from c in ctx.Customers where c.City.Contains("A") select c).Except

            (from c in ctx.Customers where c.ContactName.StartsWith("A") select c).OrderBy(c => c.ContactName);