ORM - EF--Linq语法详细 - 《.Net 学习历程》

一、查询

一、查询

1. 简单的linq语法

Linq语法：
  var data=from a in db.Areas select a ;
Lamda语法：
  var data=db.Areas;
sql语法：
  string sqlStr=" SELECT * FROM Areas  ";

2. 带where的查询

Linq语法：
var data=from a in db.orderInfo 
        where a.orderId > 20 
        select a ;
Lamda语法：
var data=db.orderInfo.Where( t=>t.orderId > 20 ) ;
sql语法：
string sqlStr=" SELECT * FROM orderInfo WHERE orderId > 20 ";

3. 简单的函数计算（count，min，max，sum）

Linq语法：
  var data=( from a in db.orderInfo select a ).Max( p=>p.orderId ) ;//查询该表中最大编号Id
  var data=( from a in db.orderInfo select a ).Min( p=>p.orderId ) ;//查询该表中最小编号Id
  var data=( from a in db.orderInfo select a ).Count() ;//查询该表数据总条数
  var data=( from a in db.orderInfo select a ).Sum( p=>p.orderMoney ) ;//查询该表中所有消费额的总数（求和）
Lamda语法：
  var data=db.orderInfo.Max( t=>t.orderId );//查询该表中最大编号Id
  var data=db.orderInfo.Min( t=>t.orderId );//查询该表中最小编号Id
  var data=db.orderInfo.Count();//查询该表数据总条数
  var data=db.orderInfo.Sum( t=>t.orderMoney );//查询该表中所有消费额的总数（求和）
sql语法：
  string sqlStr=" SELECT MAX(orderId) FROM orderInfo ";
  string sqlStr=" SELECT MIN(orderId) FROM orderInfo ";
  string sqlStr=" SELECT COUNT(*) FROM orderInfo ";
  string sqlStr=" SELECT SUM(orderMoney ) FROM orderInfo ";

4. 排序order by desc/asc

Linq语法：
var data=from a in db.orderInfo 
        where a.orderId > 20 
        orderby a.orderId descending  //倒序
        // orderby a.orderId ascending //正序
        select a ;//倒序排序，升序可用ascending关键字
Lamda语法：
情况一，根据单字段排序：
var data=db.orderInfo.OrderByDescending( t=>t.orderId ).Where( t=>t.orderId > 20 ) .ToList();//倒序排序，升序可用OrderBy关键字
情况二，根据多字段主次排序：
var priceMonthEntities = priceMonthApp.GetList().OrderBy(t => t.F_Year).ThenBy(t => t.F_Month).ToList();//先根据年份升序排序，再根据月份升序排序
sql语法：
string sqlStr=" SELECT * FROM orderInfo WHERE orderId > 20 ORDER BY orderId DESC  ";//倒序排序，升序可用ASC关键字

5. top(1)

//如果取最后一个可以按倒叙排列再取值
var ss = (from r in db.Am_recProScheme                     
          select r).FirstOrDefault();
//（）linq to ef 好像不支持 Last() 
var ss1 = db.Am_recProScheme.FirstOrDefault();
//var ss1 = db.Am_recProScheme.First();          
string sssql = "select top(1) * from Am_recProScheme";

6. 跳过前面多少条数据取余下的数据

//1
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   
//2  
var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Skip(10).ToList();
//3
string sssql = "select * from  (select ROW_NUMBER()over(order by rpId desc) as rowNum, * from [Am_recProScheme]) as t where rowNum>10";

7. 分页数据查询

Linq语法：
var data=( from a in db.orderInfo select a ) .Skip((pageIndex-1) * pageSize).Take(pageSize).ToList();//pageIndex:当前页码，pageSize：分页数据显示条数
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  
Lamda语法：
var data=db.orderInfo.Skip((pageIndex-1)* pageSize).Take(pageSize).ToList();;//pageIndex:当前页码，pageSize：分页数据显示条数
//2 Take(10): 数据从开始获取，获取指定数量（10）的连续数据
var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).Skip(10).Take(10).ToList();
sql语法：
string sqlStr=" SELECT TOP pageSize * FROM orderInfo WHERE orderId NOT IN ( SELECT TOP ( ( pageIndex - 1 ) * pageSize ) orderId FROM orderInfo )  ";//pageIndex:当前页码，pageSize：分页数据显示条数

8. 模糊查询，类似like ‘%%’

Linq语法：
  var data= from a in db.orderInfo where a.orderId.Contains(1) select a;//使用Contains关键字进行模糊匹配
Lamda语法：
  var data=db.orderInfo.Where(t=>t.F_UserId.Contains("1")).ToList();//使用Contains关键字进行模糊匹配
sql语法：
  string sqlStr=" SELECT  * FROM orderInfo WHERE orderId LIKE '%12%' ";//使用like关键字进行模糊匹配

9. 分组group by

//1
var ss = from r in db.Am_recProScheme
         orderby r.rpId descending
         group r by r.recType into n
         select new
         {
             n.Key,  //这个Key是recType
             rpId = n.Sum(r => r.rpId), //组内rpId之和
             MaxRpId = n.Max(r => r.rpId),//组内最大rpId
             MinRpId = n.Min(r => r.rpId), //组内最小rpId
         };
foreach (var t in ss)
{
    Response.Write(t.Key + "--" + t.rpId + "--" + t.MaxRpId + "--" + t.MinRpId);
}
//2
var ss1 = from r in db.Am_recProScheme
         orderby r.rpId descending
         group r by r.recType into n
         select n;
foreach (var t in ss1)
{
    Response.Write(t.Key + "--" + t.Min(p => p.rpId));
}
//3
var ss2 = db.Am_recProScheme.GroupBy(p => p.recType);
foreach (var t in ss2)
{
    Response.Write(t.Key + "--" + t.Min(p => p.rpId));
}
//4
string sssql = "select recType,min(rpId),max(rpId),sum(rpId) from Am_recProScheme group by recType";           //多字段
 var result = (from item in data                          
           group item by new { item.Name, item.Type } into items                          
           select new                          
            {    
                items.Key.Name,    
                items.Key.Type,    
                Cnt = items.Count()                          
            }).ToList();
var s = data.GroupBy(p => new { p.Type, p.Name }).Select(p=>new {          
    p.Key.Type,          
    p.Key.Name,          
    cnt=p.Count()            
    }).ToList();

Linq语法：
  var data= from a in db.orderInfo orderby a.orderId descending 
            group a by a.orderType into s select new{
            s.key,//分组字段
            s.sMoney=s.Sum(a=>a.orderMoney),//分组后算出总的消费额
            s.maMoney=s.Max(a=>a.orderMoney),//分组后算出最大的消费额
            s.miMoney=s.Min(a=>a.orderMoney)//分组后算出最小的消费额
            };
Lamda语法：
  var data=db.orderInfo.GroupBy(p => p.recType).Select(t=>t.Key).ToList();//使用GroupBy关键字进行分组查询（单个字段）
  var data=db.orderInfo.GroupBy(p =>new{ p.recType,p.orderId}).Select(t=>new{ recType=t.Key.recType,orderId=t.Key.orderId}).ToList();//使用GroupBy关键字进行分组查询（多个字段）
sql语法：
  string sqlStr=" SELECT  orderType ,SUM(orderMoney),MAX(orderMoney),MIN(orderMoney) FROM orderInfo GROUP BY orderType ";//使用 GROUP BY关键字进行分组查询

10. 连接查询

//1
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;
//2
var ss1 = db.Am_recProScheme.Join(db.Am_Test_Result, p => p.rpId, r => r.rsId, (p, r) => p).OrderByDescending(p => p.rpId).ToList();
//3
string sssql = "select r.* from  [Am_recProScheme] as r inner join [dbo].[Am_Test_Result] as t on r.[rpId] = t.[rsId] order by r.[rpId] desc";

11. sql中的In

Linq语法：
var data= from a in db.orderInfo 
            where (new int?[2213,43311,32422]).Contains(a.orderId) 
            select a ; //使用join关键字进行表连接
Lamda语法：
var data=db.orderInfo.Where(t=>(new int?[2213,43311,32422]).Contains(t.orderId)).ToList(); //使用Join关键字进行表连接
sql语法：
string sqlStr=" SELECT  *  FROM orderInfo  WHERE orderId IN (2213,43311,32422)  ";//使用Join关键字进行表连接组查询

12. 关于多表关联查询的语句

Linq语法：
var data= from a in db.orderInfo join e in  db.orderType on a.orderTypeId equals e.id select r ; //使用join关键字进行表连接
var query=from t in db.orderInfo join s in db.orderType on t.orderTypeId equals s.id select 
new {
    orderId=t.id,
    orderTypeName=s.name,
    ...
}
Lamda语法：
var data=db.orderInfo.Join(db.orderType,t=>t.orderTypeId,s=>s.id,(t,s)=>t).OrderByDescending(t=>t.orderId).
Select(
        t=> new{
         orderId=t.t.id,
         orderTypeName=t.s.name,
         ...
      }).ToList(); //使用Join关键字进行表连接
EF Core中的写法：
var data=db.orderInfo.Join(db.orderType,t=>t.orderTypeId,s=>s.id,(t,s)=>new{
orderId=s.Id,
.....
}).toList();
sql语法：（sql语句表关联有多种方法，在此只举一例）
string sqlStr=" SELECT  *  FROM orderInfo  o ,orderType t WHERE o.orderTypeId=t.id ORDER BY  t.createDate ";//使用Join关键字进行表连接组查询

13. 关于去重查询的语句

Linq语法：
var data= from a in db.orderInfo group p by new {a.orderTypeId} into _group select _group.FirstOrDefault(); //使用group关键字进行表数据去重
var data= from a in db.orderInfo group p by new {a.orderTypeId,...} into _group select _group.FirstOrDefault(); //使用group关键字对多个字段进行表数据去重
Lamda语法：
单个去重：
var data=db.orderInfo.GroupBy(t=>t.orderTypeId).Select(r => r.First()).ToList(); //使用GroupBy关键字进行表数据去重
var data=db.orderInfo.DistinctBy(t=>t.orderTypeId).ToList(); //使用DistinctBy关键字进行表数据去重
多个字段去重：
var data=db.orderInfo.GroupBy(t=>new{t.orderTypeId,...}).Select(r => r.First()).ToList(); //使用GroupBy关键字对多个字段进行表数据去重
var data=db.orderInfo.DistinctBy(t=>new{t.orderTypeId,...}).ToList(); //使用DistinctBy关键字对多个字段进行表数据去重
sql语法：
string sqlStr=" SELECT DISTINCT  orderTypeId  FROM orderInfo   ";//使用DISTINCT  关键字进行表数据去重
string sqlStr=" SELECT orderTypeId  FROM orderInfo GROUP BY  orderTypeId   ";//使用GROUP BY关键字进行表数据去重