如何将我的结果限制为我需要的行？答案

【问题标题】：How to limit my results to only the rows I need?如何将我的结果限制为我需要的行？
【发布时间】：2018-11-23 04:11:11
【问题描述】：

这是我目前拥有的用于提取前 2 个联系人的代码，但是因为当我将 USERID 带入图片时，每家公司都有超过 2 个联系人（这是必需的），它为我提供了包含公司所有用户 ID 的行，尽管他们不是我的前 2 个联系人。

select companyid, 
 userid,
(case when seqnum = 1 then username end) as  Contact1,
(case when seqnum = 2 then username end) as  Contact2,


from (
select *, row_number() over (partition by companyid order by username) as 
seqnum from 
( SELECT b.userid, username, a.companyid from [UsersInCompanies] a
JOIN [Companies] c on a.companyid = c.companyid 
join [aspnet_Users] b on a.userid = b.userid ) t ) l

我得到的结果集

CompanyID Userid  Contact1  Contact2 
1         xyz-78  Jane Doe1  NULL    
1         uik-90  NULL       JD2    
1         jkl-70  NULL       NULL
1         abc-60  NULL       NULL

想要的结果

CompanyID Userid  Contact1  Contact2 
1         xyz-78  JaneDoe1  NULL    
1         uik-90  NULL       JaneDoe2

我应该使用某种 COUNT 和 TOP 函数吗？

【问题讨论】：

尝试按seqnum <= 2过滤
*在查询末尾的WHERE 子句中过滤：WHERE seqnum <= 2。复制、粘贴、运行、完成。
您有一个不必要的额外子查询。 This should get you there
Calculate top two performing product categories from Sales data的可能重复

标签： sql sql-server tsql select where

【解决方案1】：

您需要过滤（即seqnum <= 2），但我会将其重写为：

with t as (
        SELECT b.userid, username, a.companyid, 
               ROW_NUMBER() OVER (PARTITION BY a.companyid order by b.username) as seqnum 
        FROM [UsersInCompanies] a INNER JOIN 
             [Companies] c 
             ON a.companyid = c.companyid INNER JOIN 
             [aspnet_Users] b 
             ON a.userid = b.userid
 )
select companyid, userid,
       (case when seqnum = 1 then username end) as  Contact1,
       (case when seqnum = 2 then username end) as  Contact2
from t
where seqnum <= 2;

【讨论】：

【解决方案2】：

我觉得这样更干净

with cte as 
(
    SELECT b.userid, username, a.companyid, 
           ROW_NUMBER() OVER (PARTITION BY a.companyid order by b.username) as rn 
    FROM [UsersInCompanies] a 
    JOIN [Companies] c 
      ON a.companyid = c.companyid 
    JOIN [aspnet_Users] b 
      ON a.userid = b.userid
)
select ct1.*, cte2.username 
  from cte as cte1 
  join cte as cte2 
    on cte1.companyid = cte2.companyid
   and cte1.rn = 1
   and cte2.rn = 2

【讨论】：