九、操作(在结果中搜索+查询该表,单独几个字段查询，通过子查询方式查询)

一、Left Join 两种情况

1、A表有5个，以A表为条件，查询满足跟着A行，不满足的字段为Null， 共计5行；

2、A表有5个，以A表为条件，查询满足A表一条记录的有两条，那个显示共计6行；

二、子查询 两种情况

1、两种情况，第一个 查询字段都来自一个表，个别字段(三四个字段来别别的表的情况下--left join 适合多字段)

2、从结果集中查询的时候使用--（分两种，1、当筛选条件来查询用子查询的结果时，筛选的条件是子查询里sql的列名，要想解决：

1、提前判断是否包含该子sql列名去查询 取值 ，找到关联的外层sql字段 限制。

2、还是加字查询，将查询的结果集（包含子列）的结果当做结果集----因为结果集包含子的列，用select * from 该结果集  ） ，当然这里，where 的条件就要加在 外面，拼接的sql是整体到数据库查询，

例如 ：

代码如下:

        public int GetDataTableByCount2(string Where) 
        {
            string Sql = "select Id,CityId,CreateUser,AreaName,MoneySelf,LoanNo,adddate CreateTime,ProductName,BitType,PersonName,MoneyOther,ExpectedMoney,MoneyCredit,MoneyReal,AgentUser,HouseUser,RiskCtrlUser,CheckUser,HouseArea,Status,(select ClassName from Tbl_Class where Id = a.CityId) as city,(select AdminNickName from tbl_admin where AdminName = a.AgentUser) as QuDaoNickName, (select AdminNickName from tbl_admin where AdminName = a.HouseUser) as HouseUserNickName,(select AdminNickName from tbl_admin where AdminName = a.RiskCtrlUser) as RiskCtrlUserNickName,(select AdminNickName from tbl_admin where AdminName = a.CreateUser) as JinJianNickName,(select CreateUser from tbl_admin where AdminName = a.AgentUser) as YeWuZhuanYuan,('冯东君') as YeWuZhuGuan,('江威') as RiskZhuGuan,('洪文') as CheckZhuGuan,(select top 1 AdminNickName from tbl_admin where AdminName = (select CreateUser from tbl_admin where AdminName = a.AgentUser) )as YeWuZhuanYuanNickName,(select top 1 TotalAmount from tbl_pay where LoanNo = a.LoanNo and TradeSubject='服务费') as HouseMoney ,(select top 1 300 from tbl_pay where LoanNo = a.LoanNo and IsOverTime = 1) as HouseMoneyElse from tbl_loan a where dealflag=0";
            if (Where != "") Sql = "select count(*) from (" + Sql + ") tbl where " + Where; //结果集 满足 where 查询条件的 总数    （里面 结果集中包含子sql 的列）
            int RecordNum = (int)DBHelper.ExecuteScalar(this.connection, CommandType.Text, Sql);
            return RecordNum;
        }

        // 返回条件返回分页数据
        /// </summary>
        public DataTable GetDataTableByPage2(int PageSize, int PageIndex, string Where, string Order)
        {
            //string Sql = "select *,(select count(*) from tbl_loanpic where dealflag=0 and lp_classbig='视频' and loanid=Tbl_Loan.id) as loanvideonum,(select count(*) from tbl_loanpic where dealflag=0 and lp_classbig='下户' and loanid=Tbl_Loan.id) as loanpicnum,(select isnull(min(adddate),'') from tbl_loanpic where dealflag=0 and lp_classbig='下户' and loanid=Tbl_Loan.id) as loanpictime," + GetDataTableByCount2(Where) + " as RecordNum,(select top 1 adminnickname from Tbl_Admin where adminname=Tbl_Loan.AgentUser) as AgentName,(select top 1 adminlevel from Tbl_Admin where adminname=Tbl_Loan.AgentUser) as AgentLevel,(select top 1 adminnickname from Tbl_Admin where adminname=Tbl_Loan.CreateUser) as CreateName,(select count(1) from Tbl_Loan a where a.PersonName= Tbl_Loan.PersonName and a.DealFlag=0 and a.CityId=Tbl_Loan.CityId having count(1) >1) count from Tbl_Loan where [DealFlag]=0";
            string Sql = "select Id,CityId,CreateUser,AreaName,MoneySelf,LoanNo,adddate CreateTime,ProductName,BitType,PersonName,MoneyOther,ExpectedMoney,MoneyCredit,MoneyReal,AgentUser,HouseUser,RiskCtrlUser,CheckUser,HouseArea,Status,(select ClassName from Tbl_Class where Id = a.CityId) as city,(select AdminNickName from tbl_admin where AdminName = a.AgentUser) as QuDaoNickName, (select AdminNickName from tbl_admin where AdminName = a.HouseUser) as HouseUserNickName,(select AdminNickName from tbl_admin where AdminName = a.CreateUser) as JinJianNickName,(select CreateUser from tbl_admin where AdminName = a.AgentUser) as YeWuZhuanYuan,('冯东君') as YeWuZhuGuan,('江威') as RiskZhuGuan,('洪文') as CheckZhuGuan,(select top 1 AdminNickName from tbl_admin where AdminName = (select CreateUser from tbl_admin where AdminName = a.AgentUser) )as YeWuZhuanYuanNickName,(select top 1 TotalAmount from tbl_pay where LoanNo = a.LoanNo and TradeSubject='服务费') as HouseMoney ,(select top 1 300 from tbl_pay where LoanNo = a.LoanNo and IsOverTime = 1) as HouseMoneyElse from tbl_loan a where dealflag=0";
            if (Where != "") Sql = "select * from ("+ Sql + ") tbl where " + Where;//在结果集中 查询 满足 where 条件的数据
            if (Order != "") Sql += " order by " + Order;
            int startRecord = PageSize * (PageIndex - 1);
            int endRecord = PageSize;
            DataTable dt = DBHelper.ExecuteDataTablePage(this.connection, CommandType.Text, Sql, startRecord, endRecord);
            return dt;
        }

        public dynamic GetDataTableByCount3(int PageSize, int PageIndex, string Where, string Order)//在结果集中统计满足条件的金额
        {
            string Sql = "select Id,CityId,CreateUser,AreaName,MoneySelf,LoanNo,adddate CreateTime,ProductName,BitType,PersonName,MoneyOther,ExpectedMoney,MoneyCredit,MoneyReal,AgentUser,HouseUser,RiskCtrlUser,CheckUser,HouseArea,Status,(select ClassName from Tbl_Class where Id = a.CityId) as city,(select AdminNickName from tbl_admin where AdminName = a.AgentUser) as QuDaoNickName,(select AdminNickName from tbl_admin where AdminName = a.HouseUser) as HouseUserNickName, (select AdminNickName from tbl_admin where AdminName = a.RiskCtrlUser) as RiskCtrlUserNickName,(select AdminNickName from tbl_admin where AdminName = a.CreateUser) as JinJianNickName,(select CreateUser from tbl_admin where AdminName = a.AgentUser) as YeWuZhuanYuan,('冯东君') as YeWuZhuGuan,('江威') as RiskZhuGuan,('洪文') as CheckZhuGuan,(select top 1 AdminNickName from tbl_admin where AdminName = (select CreateUser from tbl_admin where AdminName = a.AgentUser) )as YeWuZhuanYuanNickName,(select top 1 TotalAmount from tbl_pay where LoanNo = a.LoanNo and TradeSubject='服务费') as HouseMoney ,(select top 1 300 from tbl_pay where LoanNo = a.LoanNo and IsOverTime = 1) as HouseMoneyElse from tbl_loan a where dealflag=0";
            //if (Where != "") Sql += " and " + Where;
            //if (Order != "") Sql += " order by " + Order;

            string Sql1 = "select sum(MoneyReal) SumMoneyreal from (" + Sql + ") temp where "+ Where;//总放款金额
            int result1 = 0;
            var res = DBHelper.ExecuteScalar(this.connection, CommandType.Text, Sql1);
            if (!Convert.IsDBNull(res))
            {
                result1 = Convert.ToInt32(res);
            }
            string Sql2 = "select sum(HouseMoney) SumHouseMoney from (" + Sql + ") temp where " + Where;//总下户费
            object res2 = DBHelper.ExecuteScalar(this.connection, CommandType.Text, Sql2);
            decimal result2=0;
            if (!Convert.IsDBNull(res2))
            {
                result2 = Convert.ToDecimal(res2);
            }
            Tuple<int, decimal> result = new Tuple<int, decimal>(result1, result2);
            return result;
        }

 

三、数据多行转一行

比如有一个表，里面有三行数据，name分别是： name 01 02 03 现在要把这三个值转换成一行，显示为： name 01,02,03

就会用到这个，for xml path 进行拼接

三、排序，也可以去掉重复（过滤有多条的数据，而非真正意义去重）

--单独 order by 对 loanId 排序
select id,ROW_NUMBER() over(order by loanId) as rows  from Tbl_LoanLog

----partition by 必须使用 loanId 排序
select id,ROW_NUMBER() over(partition by loanId order by loanId) as rows  from Tbl_LoanLog 

----partition by 必须使用 loanId 排序  但是为了 row 是一个 
     SELECT * FROM 
        ( 
            SELECT a.status,a.id,ROW_NUMBER() over(partition by loanId order by loanId) as rows  from Tbl_LoanLog
            LEFT JOIN  Tbl_Loan a ON Tbl_LoanLog.LoanID=a.Id
        )
     AS vmtab where vmtab.rows =1 

----但是但是还是没有解决 ，我需要的去重的数据 ，而非去掉有多行的数据  用distinct

 DISTINCT的使用 distinct必须放在开头

（实际上是根据LoanID和status、Id、CityId，CreateUser、AreaName 六个字段来去重的）

 简化

最终解决

 首先:

理清关系

-- 首先 Tbl_Loan 表 a表       Tbl_LoanLog  b表
-- 情况 a表有正式和测试数据两种,  a正式数据则 b表有对应记录（多条，随着a表的状态，就会生成一条）,a表里测试数据,则b 表是没有任何生成记录的。
-- 显示a表的正式数据

--注意: a表里面状态会变，   比如 a 表 tbll.Status=N'评估完成' 则有  1252 ,状态具体有（评估完成/ 待审核，已审核...）

--而通过 b 表记录 评估完成的 的进件 1818  则是因为总件数的原因 , 现在停留在评估完成的状态 有1252 ，
--原本1818-1252 剩下的则是进入其他状态的，log状态日志记录是唯一的，所以现在直接查询a表是是很少的,那是因为当前的进件状态


-- 这种方式 1819条 以数据表为准的
select count(*) from Tbl_Loan a where a.Id in (SELECT DISTINCT b.LoanId from Tbl_LoanLog b where b.status='评估完成') 

--以下都是 log 表为准的 条数
--子查询方式 1818 条
SELECT count(*) FROM 
( 
    select tbll.status,tbl.ID
    from Tbl_LoanLog as tbll LEFT JOIN Tbl_Loan as tbl ON tbll.LoanID=tbl.Id
    WHERE tbl.DealFlag=0 and tbll.DealFlag=0 
)
AS vmtab where  status='评估完成'

--left 方式 1818 条
select Count(*) 
from Tbl_LoanLog as tbll LEFT JOIN Tbl_Loan as tbl ON tbll.LoanID=tbl.Id
WHERE tbl.DealFlag=0 and tbll.DealFlag=0  and tbll.status='评估完成'

--这种方式 也是 1818 条
select 
SUM(CASE  when tbll.status='评估完成' THEN 1 ELSE 0 END ) as TotalNum
from Tbl_LoanLog as tbll LEFT JOIN Tbl_Loan as tbl ON tbll.LoanID=tbl.Id
WHERE tbl.DealFlag=0 and tbll.DealFlag=0 


--排除log 评估状态根据 LoanId分组后状态 评估完成是否会出现两条
select a.LoanId from  Tbl_LoanLog a where status='评估完成' GROUP BY a.LoanId HAVING count(a.loanId) = 2

 最终还是没有解决重复

解决办法 select  * from Tbl_Loan   where in id in ( select  LoanId  from  Tbl_LoanLog)    --in 不用考虑 log 里面的

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原文地址：https://www.cnblogs.com/fger/p/11097891.html