using System; using System.Collections; using System.Collections.Generic; using System.Data; using System.IO; using System.Linq; using Newtonsoft.Json; namespace CLibrary.ConsoleApp { class Program { static void Main(string[] args) { var tableAAA = "
Linq 中的 left join 表A User: 表B UserType: Linq: from t in UserType join u in User on t.typeId equal u.typeId into newtable from newtable.DefaultIfEmpty() select table in newtable;
关于linq的多表联查效果的实现: 后台多表查询 内连接: SELECT [Extent2].[partID] AS [partID], [Extent1].[userName] AS [userName], [Extent3].[partName] AS [partName]FROM [dbo].[User] AS [Extent1]INNER JOIN [dbo].[User_partB] AS [Extent2] ON [Extent1].[userGUID] = [Extent2].[
Suppose you have a tblRoom and tblUserInfo. Now, you need to select all the rooms regardless of whether the room has user information or not. This calls for a LEFT JOIN which will select everything from the LEFT side (the room side) regardless of the
================START============================== 来了一个mail说是job跑得很慢,调查下原因 先来看下sql: SELECT h.order_no AS SO_no, h.order_type, h1.order_no AS po_no, l1.order_line_key AS PO_LKEY, l1.shipn
驱动表与被驱动表 先了解在join连接时哪个表是驱动表,哪个表是被驱动表:1.当使用left join时,左表是驱动表,右表是被驱动表2.当使用right join时,右表时驱动表,左表是驱动表3.当使用join时,mysql会选择数据量比较小的表作为驱动表,大表作为被驱动表 join查询如何选择驱动表与被驱动表 在sql优化中,永远是以小表驱动大表. 例如: A是小表,B是大表 使用left join 时,则应该这样写select * from A a left join B b on a.c
var query =from a in this.ObjectContext.siteInfo join b in this.ObjectContext.shopInfo on a.siteID equals b.siteID group new {a,b} by new { a.Lon, a.Lat, a.siteID, b.date} into g select new site_shopInfo{ SiteID=g.Key.siteID, Longitude=g.Key.Lon, Lat
