Linq

Posted 2020-10-21 人生如棋，落子无悔

 efEntities tc = new efEntities();

 显式 LINQ 语法的一个好处是它使操作符顺序更加明确。对于前一个示例，可以很清楚的看到它从 employees 集合开始，然后调用 Where（），最后调用 Select（）。

Linq To Entity表达式查询

基本查询：var ss=from s in tc.table select s;

带where的查询语句：var ss=from s in tc.table where s.id>100 select s;

简单的函数计算：（count，min，max，sum）

                      var ss=(from s in tc.table select s).max(s=>s.id)

                      var ss=(from s in tc.table select s).count();

排序order by desc/asc(

descending  //倒序，

ascending   //正序

)

 

var ss=(from s in tc.table order by id descending select s)

 

top(5)： var ss = (from s in tc.table_ip select s).Take(5);  

top(1):    var ss = (from s in tc.table_ip select s).First();

 

跳过前面多少条数据取余下的数据

  var ss = (from r in db.Am_recProScheme
                      orderby r.rpId descending
                      select r).Skip(10); //跳过前10条数据，取10条之后的所有数据   
           

            string sssql = "select * from  (select ROW_NUMBER()over(order by rpId desc) as rowNum, * from [Am_recProScheme]) as t where rowNum>10";

分页数据查询

   var ss = (from r in db.Am_recProScheme
                      where r.rpId > 10
                      orderby r.rpId descending
                      select r).Skip(10).Take(10); //取第11条到第20条数据                   

            //2 Take(10): 数据从开始获取，获取指定数量（10）的连续数据

包含，类似like \'%%\'    countains

         var ss=(from r in tc.table where r.ip.Contains("196" select r)

 

分组 group by 

        var ss = (from s in tc.table_ip     group s by s.city into t    select new   {  t.Key, ipCount=t.Count()   }); //方法1

        var ss=(from s in tc.table_ip group s by tc.city into t select t)   

           foreach (var t in ss)

            {
                Response.Write(t.Key + "--" + t.Min(p => p.rpId));                      //方法2
            }

联合查询

  var ss = from r in db.Am_recProScheme
                     join w in db.Am_Test_Result on r.rpId equals w.rsId
                     orderby r.rpId descending
                     select r;

sql中的In

var ss = from p in db.Am_recProScheme
                              where (new int?[] { 24, 25,26 }).Contains(p.rpId)
                              select p;
            foreach (var p in ss)
            {
                Response.Write(p.Sorts);
            }
            //2
            string st = "select * from Am_recProScheme where rpId in(24,25,26)";

基于方法的查询

带where的查询语句：tc.table(s=>s.id>100);

简单的函数计算：（count，min，max，sum）

                  var ss=tc.table.max(s=>s.id);

                  var ss=tc.table.count();

排序order by desc/asc

                 var ss=  tc.table_ip.OrderBy(s=>s.ip).OrderByDescending(s=>s.id);   //根据ip升序，再根据id降序

 

top(5)： var ss = tc.table.Take(5);  

top(1):    var ss = tc.table.First();

 

跳过前面多少条数据取余下的数据

  var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Skip(10).ToList();

分页数据查询     

     var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).Skip(10).Take(10).ToList();

包含，类似like \'%%\'

         var ss=tc.table.where(s=>s.ip.countain("198"))

分组 group by 

var ss2 = db.Am_recProScheme.GroupBy(p => p.recType);
            foreach (var t in ss2)
            {
                Response.Write(t.Key + "--" + t.Min(p => p.rpId));

  var ss = from r in db.Am_recProScheme
                     join w in db.Am_Test_Result on r.rpId equals w.rsId
                     orderby r.rpId descending
                     select r;

联合查询
var ss=

db.Am_recProScheme.join( db.Am_Test_Result,ps=>ps.id,tr=>tr.id,(ps,tr)=>ps).OrderByDescending(p => p.rpId).ToList();

)


参考：http://www.cnblogs.com/knowledgesea/p/3897665.html