Linq to SQL 的用法
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python的to_sql用法
Python的to_sql用法指的是使用Python语言中的pandas库中的to_sql方法将数据写入SQL数据库中。
to_sql方法可以将DataFrame对象的数据写入到SQL数据库的表中,并支持更新、替换和追加数据等操作。
使用to_sql方法可简化数据导入过程,提高数据库操作的效率和准确性。
在使用to_sql方法时,需要先创建一个数据库连接对象,然后将DataFrame对象与目标表名、数据库连接对象等参数传入to_sql方法中即可完成数据写入操作。
to_sql方法可以自动根据DataFrame对象的列名和数据类型生成相应的表结构,也可以手动指定表结构。
需要注意的是,在使用to_sql方法前,需要确保已经安装了相应的数据库驱动程序。
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Linq语法详细(三种⽅式:linq、Lambda、SQL语法)三种⽅式:linq、Lambda、SQL语法1.简单的linq语法//1var ss = from r in db.Am_recProSchemeselect r;//2var ss1 = db.Am_recProScheme;//3string sssql = "select * from Am_recProScheme";2.带where的查询//1var ss = from r in db.Am_recProSchemewhere r.rpId > 10select r;//2var ss1 = db.Am_recProScheme.Where(p => p.rpId > 10);//3string sssql = "select * from Am_recProScheme where rpid>10";3.简单的函数计算(count,min,max,sum)//1////获取最⼤的rpId//var ss = (from r in db.Am_recProScheme// select r).Max(p => p.rpId);////获取最⼩的rpId//var ss = (from r in db.Am_recProScheme// select r).Min(p => p.rpId);//获取结果集的总数//var ss = (from r in db.Am_recProScheme// select r).Count();//获取rpId的和var ss = (from r in db.Am_recProSchemeselect r).Sum(p => p.rpId);//2//var ss1 = db.Am_recProScheme.Max(p=>p.rpId);//var ss1 = db.Am_recProScheme.Min(p => p.rpId);//var ss1 = db.Am_recProScheme.Count() ;var ss1 = db.Am_recProScheme.Sum(p => p.rpId);Response.Write(ss);//3string sssql = "select max(rpId) from Am_recProScheme";sssql = "select min(rpId) from Am_recProScheme";sssql = "select count(1) from Am_recProScheme";sssql = "select sum(rpId) from Am_recProScheme";4.排序order by desc/ascvar ss = from r in db.Am_recProSchemewhere r.rpId > 10orderby r.rpId descending //倒序// orderby r.rpId ascending //正序select r;//正序var ss1 = db.Am_recProScheme.OrderBy(p => p.rpId).Where(p => p.rpId > 10).ToList();//倒序var ss2 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).ToList();string sssql = "select * from Am_recProScheme where rpid>10 order by rpId [desc|asc]";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_recProSchemeselect 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//1var ss = (from r in db.Am_recProSchemeorderby r.rpId descendingselect r).Skip(10); //跳过前10条数据,取10条之后的所有数据//2var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Skip(10).ToList();//3string 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//1var ss = (from r in db.Am_recProSchemewhere r.rpId > 10orderby r.rpId descendingselect 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var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).Skip(10).Take(10).ToList();//3string sssql = "select * from (select ROW_NUMBER()over(order by rpId desc) as rowNum, * from [Am_recProScheme]) as t where rowNum>10 and rowNum<=20";8.包含,类似like '%%'//1var ss = from r in db.Am_recProSchemewhere r.SortsText.Contains("张")select r;//2var ss1 = db.Am_recProScheme.Where(p => p.SortsText.Contains("张")).ToList();//3string sssql = "select * from Am_recProScheme where SortsText like '%张%'";9.分组group by//1var ss = from r in db.Am_recProSchemeorderby r.rpId descendinggroup r by r.recType into nselect new{n.Key, //这个Key是recTyperpId = n.Sum(r => r.rpId), //组内rpId之和MaxRpId = n.Max(r => r.rpId),//组内最⼤rpIdMinRpId = 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);}//2var ss1 = from r in db.Am_recProSchemeorderby r.rpId descendinggroup r by r.recType into nselect n;foreach (var t in ss1){Response.Write(t.Key + "--" + t.Min(p => p.rpId));}//3var ss2 = db.Am_recProScheme.GroupBy(p => p.recType);foreach (var t in ss2){Response.Write(t.Key + "--" + t.Min(p => p.rpId));}//4string sssql = "select recType,min(rpId),max(rpId),sum(rpId) from Am_recProScheme group by recType";10.连接查询//1var ss = from r in db.Am_recProSchemejoin w in db.Am_Test_Result on r.rpId equals w.rsIdorderby r.rpId descendingselect r;//2var ss1 = db.Am_recProScheme.Join(db.Am_Test_Result, p => p.rpId, r => r.rsId, (p, r) => p).OrderByDescending(p => p.rpId).ToList(); //3string 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//1var ss = from p in db.Am_recProSchemewhere (new int?[] { 24, 25,26 }).Contains(p.rpId)select p;foreach (var p in ss){Response.Write(p.Sorts);}//2string st = "select * from Am_recProScheme where rpId in(24,25,26)";。
join在sql中的用法join在SQL中的用法在SQL中,join是一种常用的操作,用于将多个表中的数据连接在一起。
通过join操作,可以从多个表中检索数据并根据指定的条件将它们组合在一起。
本文将详细介绍join的用法,包括不同类型的join操作以及它们的应用场景。
一、什么是join操作在数据库中,数据通常存储在多个表中,这些表之间通过关系进行连接。
而join操作就是通过某种条件连接多个表,并返回满足条件的数据。
join 操作可以根据连接条件的不同分为多种类型,如内连接、外连接和交叉连接等。
二、内连接内连接是最常用的join操作之一。
当执行内连接时,只有满足连接条件(即两个表中对应列的值相等)的行才会被返回。
内连接可以使用关键字INNER JOIN或简单地使用JOIN来实现。
下面是一个示例,假设我们有两个表- "顾客"表和"订单"表:表:顾客顾客ID 姓名地址1 张三北京市2 李四上海市3 王五广州市表:订单订单ID 顾客ID 订单日期1 1 2022-01-012 2 2022-01-023 1 2022-01-03我们可以使用以下SQL语句来执行内连接操作:SELECT *FROM 顾客INNER JOIN 订单ON 顾客.顾客ID = 订单.顾客ID;将上述SQL语句执行后,将返回一个新的表,包含了"顾客"表和"订单"表中符合连接条件的行。
结果如下:顾客ID 姓名地址订单ID 顾客ID 订单日期1 张三北京市 1 1 2022-01-011 张三北京市 3 1 2022-01-032 李四上海市 2 2 2022-01-02三、外连接外连接也是一种常用的join操作。
与内连接不同的是,外连接会返回连接表中的所有行,即使没有满足连接条件的行。
外连接可以分为左外连接、右外连接和全外连接等几种类型。
1.左外连接左外连接即包含左表中的所有行,以及右表中与左表连接条件匹配的行。
linq转化为sql语句的方法Linq转化为SQL语句的方法概述Linq(Language Integrated Query)是微软推出的一种用于查询和操作数据的统一编程模型。
它可以在不同的数据源上执行查询,例如关系型数据库、XML文档等。
在开发过程中,我们常常需要将Linq 表达式转化为相应的SQL语句,以便对数据库进行操作。
本文将详细介绍多种将Linq转化为SQL语句的方法。
1. LINQ to SQL基本概念LINQ to SQL是一种将LINQ查询转化为SQL语句的方法。
它是Entity Framework的一部分,提供了一种直接在.NET应用程序中使用对象来表示和操作关系型数据库的方式。
在LINQ to SQL中,可以通过DataContext对象来执行查询,并将查询结果转化为SQL语句。
示例代码using System;using ;using ;public class Program{public static void Main(){// 创建DataContext对象,连接数据库DataContext context = new DataContext("Data Sour ce=.;Initial Catalog=MyDatabase;Integrated Security=True ");// 创建查询表达式var query = from c in <Customer>()where == "Beijing"select c;// 执行查询并获取SQL语句string sql = (query).CommandText;// 输出SQL语句(sql);}}2. Entity Framework基本概念Entity Framework是微软推出的一种对象关系映射(ORM)工具,可以映射.NET对象与数据库中的表、视图等关系。
Linq基础+Lambda表达式对数据库的增删改及简单查询⼀、Linq to sql 类⾼集成化的数据库访问技术使⽤Linq可以代替之前的,省去了⾃⼰敲代码的实体类和数据访问类的⼤量⼯作实体类:添加⼀个Linq to sql 类 ----选择要使⽤的数据库---- 拖⼊要使⽤的表需要⽴即保存就相当于创建实体类如果进⾏属性扩展,在App_Code下添加类,类名同表名⼀致。
将该类在访问修饰符后加上partial,将该类定为实体类的⼀部分数据访问类:不⽤在App_Code下再建数据访问类了。
直接在使⽤数据访问类的地⽅⽤数据库上下⽂进⾏编写。
ers.ToList(); //是将Users表转化为⼀个泛型集合。
也就相当于查询全部的⽅法⼆、利⽤Linq对数据库进⾏相关操作1、添加数据每⼀条数据都是⼀个实体类对象。
先将其实例化出来,再给对象的每个属性赋值。
在数据访问类中进⾏添加数据操作添加的⽅法:ers.InsertOnSumbit(对象);⽅法执⾏结束后提交对数据库的更改:con.SubmitChanges();2、删除数据删除数据前要先查到这条数据再进⾏删除操作通过ids进⾏查询这条数据返回⼀个对象Users u = ers.Where(r=>r.ids.Tostring()==ids).FirstOrDefault();where括号内接的是Lambda表达式,r代表⼀个Users对象,=>是基本格式,FirstOrDefault()返回第⼀条数据或者返还空如果u不是空,则在数据访问类中进⾏删除。
ers.DeleteOnSubmit(对象);con.SubmitChanges();3、数据修改数据的修改同样也是需要先查到这条数据,将返回的这个对象的要修改的属性进⾏重新赋值最后con.SubmitChanges();4、简单数据查询直接在数据访问类中根据对象的属性进⾏查询,多个查询条件中间⽤ && 连接;如 ers.Where(r=>erName=="zhangsan" && r.PassWord=="123").FirstOrDefault();。
第一步、创建了一个SQL Server数据源先创建数据库又建了一个User表相信这些都是小儿科的东西了,我就不再多说了。
第二步、添加一个LINQ to SQL类我创建了一个User.dbml的LINQ to SQL类然后从服务器资源管理器中把表拖拽到视图中,可以双击视图中表的标题来重命名。
最后保存一下。
第三步、创建并执行查询namespace test{public partial class _Default : System.Web.UI.Page{protected void Page_Load(object sender, EventArgs e){if (!IsPostBack){Bind();}}private void Bind(){UserDataContextdb = new UserDataContext(); //创建一个DataContext类对象是必不可少的var user = from u in db.MyUser //在上面为它重命名为MyUser了,原来的表名为Userselect u; //这里的查询就和SQL差不多了GridView1.DataSource = user; //绑定数据源GridView1.DataBind();}//插入信息protected void btnAdd_Click(object sender, EventArgs e){UserDataContextdb = new UserDataContext();stringuserName = TextBox1.Text;stringuserPwd = TextBox2.Text;//db.MyUser.InsertOnSubmit(new MyUser { Name=userName,Pwd=userPwd});//上面这句和下面这句都可以实现,只不过是两种不同的方法var user = new MyUser { Name = userName, Pwd = userPwd };db.MyUser.InsertOnSubmit(user); //执行插入db.SubmitChanges(); //提交对数据库做的修改Bind();}后面的删除、更新就跟上面的插入大同小异了,只是查询和执行查询所用到的方法不同而已。
LINQ系列:LINQtoSQLGroupbyHaving分组1. 简单形式var expr = from p in context.Productsgroup p by p.CategoryID into gselect g;foreach (var item in expr){Console.WriteLine(item.Key);foreach (var p in item){Console.WriteLine("{0}-{1}", p.ProductID, p.ProductName);}}SELECT[Project2].[CategoryID] AS [CategoryID],[Project2].[C1] AS [C1],[Project2].[ProductID] AS [ProductID],[Project2].[CategoryID1] AS [CategoryID1],[Project2].[ProductName] AS [ProductName],[Project2].[UnitPrice] AS [UnitPrice],[Project2].[UnitsInStock] AS [UnitsInStock],[Project2].[Discontinued] AS [Discontinued]FROM ( SELECT[Distinct1].[CategoryID] AS [CategoryID],[Extent2].[ProductID] AS [ProductID],[Extent2].[CategoryID] AS [CategoryID1],[Extent2].[ProductName] AS [ProductName],[Extent2].[UnitPrice] AS [UnitPrice],[Extent2].[UnitsInStock] AS [UnitsInStock],[Extent2].[Discontinued] AS [Discontinued],CASE WHEN ([Extent2].[ProductID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]FROM (SELECT DISTINCT[Extent1].[CategoryID] AS [CategoryID]FROM [dbo].[Product] AS [Extent1] ) AS [Distinct1]LEFT OUTER JOIN [dbo].[Product] AS [Extent2] ON [Distinct1].[CategoryID] = [Extent2].[CategoryID]) AS [Project2]ORDER BY [Project2].[CategoryID] ASC, [Project2].[C1] ASC2. 最⼤值var expr = from p in context.Productsgroup p by p.CategoryID into gselect new{g.Key,MaxUnitPrice = g.Max(p => p.UnitPrice)};foreach (var item in expr){Console.WriteLine("{0}-{1}", item.Key, item.MaxUnitPrice);}SELECT[GroupBy1].[K1] AS [CategoryID],[GroupBy1].[A1] AS [C1]FROM ( SELECT[Extent1].[CategoryID] AS [K1],MAX([Extent1].[UnitPrice]) AS [A1]FROM [dbo].[Product] AS [Extent1]GROUP BY [Extent1].[CategoryID]) AS [GroupBy1]3. 最⼩值var expr = from p in context.Productsgroup p by p.CategoryID into gselect new{g.Key,MinUnitPrice = g.Min(p => p.UnitPrice)};SELECT[GroupBy1].[K1] AS [CategoryID],[GroupBy1].[A1] AS [C1]FROM ( SELECT[Extent1].[CategoryID] AS [K1],MIN([Extent1].[UnitPrice]) AS [A1]FROM [dbo].[Product] AS [Extent1]GROUP BY [Extent1].[CategoryID]) AS [GroupBy1]4. 平均值var expr = from p in context.Productsgroup p by p.CategoryID into gselect new{g.Key,AverageUnitPrice = g.Average(p => p.UnitPrice)};SELECT[GroupBy1].[K1] AS [CategoryID],[GroupBy1].[A1] AS [C1]FROM ( SELECT[Extent1].[CategoryID] AS [K1],AVG([Extent1].[UnitPrice]) AS [A1]FROM [dbo].[Product] AS [Extent1]GROUP BY [Extent1].[CategoryID]) AS [GroupBy1]5. 求和var expr = from p in context.Productsgroup p by p.CategoryID into gselect new{g.Key,TotalUnitPrice = g.Sum(p => p.UnitPrice)};SELECT[GroupBy1].[K1] AS [CategoryID],[GroupBy1].[A1] AS [C1]FROM ( SELECT[Extent1].[CategoryID] AS [K1],SUM([Extent1].[UnitPrice]) AS [A1]FROM [dbo].[Product] AS [Extent1]GROUP BY [Extent1].[CategoryID]) AS [GroupBy1]6. 计数var expr = from g infrom p in context.Productsgroup p by p.CategoryIDselect new{CategoryID = g.Key,ProductsNumber = g.Count()};var expr = from p in context.Productsgroup p by p.CategoryID into gselect new{g.Key,ProductNumber = g.Count()};var expr = context.Products.GroupBy(p => p.CategoryID).Select(g => new{CategoryID = g.Key,ProductNumber = g.Count()});SELECT[GroupBy1].[K1] AS [CategoryID],[GroupBy1].[A1] AS [C1]FROM ( SELECT[Extent1].[CategoryID] AS [K1],COUNT(1) AS [A1]FROM [dbo].[Product] AS [Extent1]GROUP BY [Extent1].[CategoryID]) AS [GroupBy1]var expr = from p in context.Productsgroup p by p.CategoryID into gselect new{g.Key,ProductNumber = g.Count(p => p.UnitsInStock > 0) };7. Where限制var expr = from p in context.Productsgroup p by p.CategoryID into gwhere g.Count() > 10select new{g.Key,ProductNumber = g.Count()};SELECT[GroupBy1].[K1] AS [CategoryID],[GroupBy1].[A2] AS [C1]FROM ( SELECT[Extent1].[CategoryID] AS [K1],COUNT(1) AS [A1],COUNT(1) AS [A2]FROM [dbo].[Product] AS [Extent1]GROUP BY [Extent1].[CategoryID]) AS [GroupBy1]WHERE [GroupBy1].[A1] > 108. 多列分组var expr = from p in context.Productsgroup p by new{p.CategoryID,p.Discontinued}into gselect new{g.Key,ProductNumber = g.Count()};SELECT[GroupBy1].[K1] AS [CategoryID],[GroupBy1].[K3] AS [C1],[GroupBy1].[K2] AS [Discontinued],[GroupBy1].[A1] AS [C2]FROM ( SELECT[Extent1].[K1] AS [K1],[Extent1].[K2] AS [K2],[Extent1].[K3] AS [K3],COUNT([Extent1].[A1]) AS [A1]FROM ( SELECT[Extent1].[CategoryID] AS [K1],[Extent1].[Discontinued] AS [K2],1 AS [K3],1 AS [A1]FROM [dbo].[Product] AS [Extent1]) AS [Extent1]GROUP BY [K1], [K2], [K3]) AS [GroupBy1]var expr = from p in context.Productsgroup p by new{p.CategoryID,p.Discontinued}into gselect new{g.Key.CategoryID,ProductNumber = g.Count()};SELECT[GroupBy1].[K1] AS [CategoryID],[GroupBy1].[A1] AS [C1]FROM ( SELECT[Extent1].[CategoryID] AS [K1],[Extent1].[Discontinued] AS [K2],COUNT(1) AS [A1]FROM [dbo].[Product] AS [Extent1]GROUP BY [Extent1].[CategoryID], [Extent1].[Discontinued]) AS [GroupBy1]9. 表达式var expr = from p in context.Productsgroup p by new{Criteria = p.UnitPrice > 10m}into gselect new{g.Key,ProductNumber = g.Count()};语句描述:使⽤Group By返回两个产品序列。