SQL Question: INNER JOIN(SELF JOIN) eliminates duplicate values
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Data Table 
Question: List the names of all the supervisors in alphabetical order. If the supervisor has more than one staff, his name should appear only once.
My input and output: 
Expected Output: 
Absolute beginner in SQL and new to stackoverflow, help rendered will be greatly appreciated
sql
sql-server edited Nov 15 '18 at 14:52
Eray Balkanli
4,65852347
asked Nov 15 '18 at 14:43
user9978150user9978150
12
add a comment |
Data Table
Question: List the names of all the supervisors in alphabetical order. If the supervisor has more than one staff, his name should appear only once.
My input and output:
Expected Output:
Absolute beginner in SQL and new to stackoverflow, help rendered will be greatly appreciated
sql
sql-server edited Nov 15 '18 at 14:52
Eray Balkanli
4,65852347
asked Nov 15 '18 at 14:43
user9978150user9978150
12
UseLEFT JOINinstead ofINNER JOIN
– Jean-Marc Zimmer
Nov 15 '18 at 14:45
select distinct supervisorname from ...
– jarlh
Nov 15 '18 at 14:46
SELECT * FROM staff s where exists(select 1 from staff x where x.supervisor_id = s.id);
– joop
Nov 15 '18 at 14:55
add a comment |
Data Table
Question: List the names of all the supervisors in alphabetical order. If the supervisor has more than one staff, his name should appear only once.
My input and output:
Expected Output:
Absolute beginner in SQL and new to stackoverflow, help rendered will be greatly appreciated
sql
sql-server edited Nov 15 '18 at 14:52
Eray Balkanli
4,65852347
asked Nov 15 '18 at 14:43
user9978150user9978150
12
Data Table
Question: List the names of all the supervisors in alphabetical order. If the supervisor has more than one staff, his name should appear only once.
My input and output:
Expected Output:
Absolute beginner in SQL and new to stackoverflow, help rendered will be greatly appreciated
sql
sql-server sql
sql-server edited Nov 15 '18 at 14:52
Eray Balkanli
4,65852347
asked Nov 15 '18 at 14:43
user9978150user9978150
12
edited Nov 15 '18 at 14:52
Eray Balkanli
4,65852347
asked Nov 15 '18 at 14:43
user9978150user9978150
12
edited Nov 15 '18 at 14:52
Eray Balkanli
4,65852347
edited Nov 15 '18 at 14:52
Eray Balkanli
4,65852347
edited Nov 15 '18 at 14:52
Eray Balkanli
4,65852347
4,65852347
asked Nov 15 '18 at 14:43
user9978150user9978150
12
asked Nov 15 '18 at 14:43
user9978150user9978150
12
asked Nov 15 '18 at 14:43
user9978150user9978150
12
12
UseLEFT JOINinstead ofINNER JOIN
– Jean-Marc Zimmer
Nov 15 '18 at 14:45
select distinct supervisorname from ...
– jarlh
Nov 15 '18 at 14:46
SELECT * FROM staff s where exists(select 1 from staff x where x.supervisor_id = s.id);
– joop
Nov 15 '18 at 14:55
add a comment |
UseLEFT JOINinstead ofINNER JOIN
– Jean-Marc Zimmer
Nov 15 '18 at 14:45
select distinct supervisorname from ...
– jarlh
Nov 15 '18 at 14:46
SELECT * FROM staff s where exists(select 1 from staff x where x.supervisor_id = s.id);
– joop
Nov 15 '18 at 14:55
Use
LEFT JOIN instead of INNER JOIN– Jean-Marc Zimmer
Nov 15 '18 at 14:45
Use
LEFT JOIN instead of INNER JOIN– Jean-Marc Zimmer
Nov 15 '18 at 14:45
select distinct supervisorname from ...– jarlh
Nov 15 '18 at 14:46
select distinct supervisorname from ...– jarlh
Nov 15 '18 at 14:46
SELECT * FROM staff s where exists(select 1 from staff x where x.supervisor_id = s.id);– joop
Nov 15 '18 at 14:55
SELECT * FROM staff s where exists(select 1 from staff x where x.supervisor_id = s.id);– joop
Nov 15 '18 at 14:55
add a comment |
3 Answers
3
active
oldest
votes
I think you need to find out the supervisors first by using a cte or temptable, then use it to select the names like:
;with cte as ( --supervisors
select distinct s1.Id
from Staff s1
inner join Staff s2 on s1.Id=s2.SupervisorId
)
select s.Name
from Staff s
inner join cte on s.Id = cte.Id
order by s.Name
answered Nov 15 '18 at 14:47
Eray BalkanliEray Balkanli
4,65852347
add a comment |
You can simply do:
select s.*
from staff s
where exists (select 1 from staff s2 where s.staffId = s2.supervisorid);
That is, select all staff who are supervisors.
answered Nov 15 '18 at 14:56
Gordon LinoffGordon Linoff
798k37320426
add a comment |
You could try this query:
SELECT MAX(Staff.Name) As SupervisorName
FROM Staff INNER JOIN Staff Sup
ON Staff.SupervisorID = Sup.StaffID
GROUP BY Staff.Name
ORDER BY Staff.Name ASC
answered Nov 15 '18 at 14:53
D. HurtadoD. Hurtado
966
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
I think you need to find out the supervisors first by using a cte or temptable, then use it to select the names like:
;with cte as ( --supervisors
select distinct s1.Id
from Staff s1
inner join Staff s2 on s1.Id=s2.SupervisorId
)
select s.Name
from Staff s
inner join cte on s.Id = cte.Id
order by s.Name
answered Nov 15 '18 at 14:47
Eray BalkanliEray Balkanli
4,65852347
add a comment |
I think you need to find out the supervisors first by using a cte or temptable, then use it to select the names like:
;with cte as ( --supervisors
select distinct s1.Id
from Staff s1
inner join Staff s2 on s1.Id=s2.SupervisorId
)
select s.Name
from Staff s
inner join cte on s.Id = cte.Id
order by s.Name
answered Nov 15 '18 at 14:47
Eray BalkanliEray Balkanli
4,65852347
add a comment |
I think you need to find out the supervisors first by using a cte or temptable, then use it to select the names like:
;with cte as ( --supervisors
select distinct s1.Id
from Staff s1
inner join Staff s2 on s1.Id=s2.SupervisorId
)
select s.Name
from Staff s
inner join cte on s.Id = cte.Id
order by s.Name
answered Nov 15 '18 at 14:47
Eray BalkanliEray Balkanli
4,65852347
I think you need to find out the supervisors first by using a cte or temptable, then use it to select the names like:
;with cte as ( --supervisors
select distinct s1.Id
from Staff s1
inner join Staff s2 on s1.Id=s2.SupervisorId
)
select s.Name
from Staff s
inner join cte on s.Id = cte.Id
order by s.Name
answered Nov 15 '18 at 14:47
Eray BalkanliEray Balkanli
4,65852347
answered Nov 15 '18 at 14:47
Eray BalkanliEray Balkanli
4,65852347
answered Nov 15 '18 at 14:47
Eray BalkanliEray Balkanli
4,65852347
answered Nov 15 '18 at 14:47
Eray BalkanliEray Balkanli
4,65852347
4,65852347
add a comment |
add a comment |
You can simply do:
select s.*
from staff s
where exists (select 1 from staff s2 where s.staffId = s2.supervisorid);
That is, select all staff who are supervisors.
answered Nov 15 '18 at 14:56
Gordon LinoffGordon Linoff
798k37320426
add a comment |
You can simply do:
select s.*
from staff s
where exists (select 1 from staff s2 where s.staffId = s2.supervisorid);
That is, select all staff who are supervisors.
answered Nov 15 '18 at 14:56
Gordon LinoffGordon Linoff
798k37320426
add a comment |
You can simply do:
select s.*
from staff s
where exists (select 1 from staff s2 where s.staffId = s2.supervisorid);
That is, select all staff who are supervisors.
answered Nov 15 '18 at 14:56
Gordon LinoffGordon Linoff
798k37320426
You can simply do:
select s.*
from staff s
where exists (select 1 from staff s2 where s.staffId = s2.supervisorid);
That is, select all staff who are supervisors.
answered Nov 15 '18 at 14:56
Gordon LinoffGordon Linoff
798k37320426
answered Nov 15 '18 at 14:56
Gordon LinoffGordon Linoff
798k37320426
answered Nov 15 '18 at 14:56
Gordon LinoffGordon Linoff
798k37320426
answered Nov 15 '18 at 14:56
Gordon LinoffGordon Linoff
798k37320426
798k37320426
add a comment |
add a comment |
You could try this query:
SELECT MAX(Staff.Name) As SupervisorName
FROM Staff INNER JOIN Staff Sup
ON Staff.SupervisorID = Sup.StaffID
GROUP BY Staff.Name
ORDER BY Staff.Name ASC
answered Nov 15 '18 at 14:53
D. HurtadoD. Hurtado
966
add a comment |
You could try this query:
SELECT MAX(Staff.Name) As SupervisorName
FROM Staff INNER JOIN Staff Sup
ON Staff.SupervisorID = Sup.StaffID
GROUP BY Staff.Name
ORDER BY Staff.Name ASC
answered Nov 15 '18 at 14:53
D. HurtadoD. Hurtado
966
add a comment |
You could try this query:
SELECT MAX(Staff.Name) As SupervisorName
FROM Staff INNER JOIN Staff Sup
ON Staff.SupervisorID = Sup.StaffID
GROUP BY Staff.Name
ORDER BY Staff.Name ASC
answered Nov 15 '18 at 14:53
D. HurtadoD. Hurtado
966
You could try this query:
SELECT MAX(Staff.Name) As SupervisorName
FROM Staff INNER JOIN Staff Sup
ON Staff.SupervisorID = Sup.StaffID
GROUP BY Staff.Name
ORDER BY Staff.Name ASC
answered Nov 15 '18 at 14:53
D. HurtadoD. Hurtado
966
answered Nov 15 '18 at 14:53
D. HurtadoD. Hurtado
966
answered Nov 15 '18 at 14:53
D. HurtadoD. Hurtado
966
answered Nov 15 '18 at 14:53
D. HurtadoD. Hurtado
966
966
add a comment |
add a comment |
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Use
LEFT JOINinstead ofINNER JOIN– Jean-Marc Zimmer
Nov 15 '18 at 14:45
select distinct supervisorname from ...– jarlh
Nov 15 '18 at 14:46
SELECT * FROM staff s where exists(select 1 from staff x where x.supervisor_id = s.id);– joop
Nov 15 '18 at 14:55