SQL选择查询使用分组依据

Question

How to get the TeamCount and TeamLead Name currectly

  Teams | TeamCount | TeamLead Name
-------------------------------------
| Team1 | 2         | NULL
| Team2 | 2         | NULL
| Team1 | 1         | Prashanth

Some times Team may or may not have the team lead. So we just have to show the TeamLead name as null, if team lead is not found for the team

I need some help to get the out as below

Teams | TeamCount | TeamLead Name
---------------------------------
Team1 | 3         | Prashanth
Team2 | 2         | NULL

Answer 1

...and here you go!

     create table test2 as
            select distinct c.teams,sum(c.TeamCount) as SUM,c.TeamName
     from
           (select a.Teams,a.TeamCount,b.TeamName from team as a
     left outer join
           (select * from team where TeamName ne "") as b
            on a.Teams = B.Teams) as c
     group by c.Teams;

You should try to develop these solutions by working from the inside out and build the query in steps

Answer 2

You can do this with a LEFT OUTER join between Team and TeamMembers , and including the IsLead into the join criterion, before grouping by the Team name - this will exclude non-leads:

SELECT T.Name, MIN(TM.TName) AS Lead
FROM Teams T
  LEFT OUTER JOIN TeamMembers TM 
    ON TM.TeamId = T.Id AND TM.IsLead = 1
GROUP BY T.Name;

SqlFiddle here

The TeamCount doesn't seem to make sense here - if you can elaborate on how you intend deriving it, perhaps we can help here

PS : You've tagged both MySql and Oracle - don't do this please.

Answer 3

Here you are:

MySQL:

select team as teamId, sum(teamcount) as teamcount,
  (select teamleadname from teams
   where teamId = teams.team and teamleadname is not null
   limit 1) as teamleadname
from teams
group by team

http://sqlfiddle.com/#!9/5889d/39

SQl Server:

declare @teams TABLE(Team varchar(20), TeamCount int, TeamLeadName varchar(20));

INSERT INTO @teams
VALUES
    ('Team1', 2, null),
    ('Team2', 2, null),
    ('Team1', 1, 'Prashanth')

select l.Team, l.TeamCount, r.TeamLeadName
from
    (select Team , sum(TeamCount) as TeamCount from @teams group by Team) as l 
    left outer join 
    (select Team, TeamLeadName 
    from 
        (select Team, TeamLeadName, row_number() over(partition by Team order by TeamLeadName desc) as roworder 
        from @teams) as o where o.roworder = 1
    ) as r
    on l.Team = r.Team

Hope this help.