Left join in sql table? - sql

Question

I have the following SQL Server table:
+-------+----------+----------+----------+
| group | subgroup | position | value |
+-------+----------+----------+----------+
| D924 | A | 50 | 9144142 |
| D924 | A | 52 | 9268118 |
| D924 | A | 60 | 9144588 |
| D924 | A | 70 | 10116006 |
| D924 | A | 110 | 9074177 |
| D924 | A | 171 | 7367052 |
| D924 | A | 180 | 10118595 |
| D924 | A | 190 | 9074522 |
| D924 | B | 150 | 12423396 |
| D955 | ... | ... | ... |
+-------+----------+----------+----------+
I need to list all the position for every subgroup within the same group
Like so:
+-------+----------+----------+----------+
| group | subgroup | position | value |
+-------+----------+----------+----------+
| D924 | A | 50 | 9144142 |
| D924 | A | 52 | 9268118 |
| D924 | A | 60 | 9144588 |
| D924 | A | 70 | 10116006 |
| D924 | A | 110 | 9074177 |
| D924 | A | 171 | 7367052 |
| D924 | A | 180 | 10118595 |
| D924 | A | 190 | 9074522 |
| D924 | A | 150 | |
| D924 | B | 50 | |
| D924 | B | 52 | |
| D924 | B | 60 | |
| D924 | B | 70 | |
| D924 | B | 110 | |
| D924 | B | 171 | |
| D924 | B | 180 | |
| D924 | B | 190 | |
| D924 | B | 150 | 12423396 |
| D955 | ... | ... | ... |
+-------+----------+----------+----------+
I would like to achieve the result table in a single SQL query. Can you advise?

Answer 1

This is simply a DISTINCT list of the position and [Group] & subgroup values with a LEFT JOIN back to the table.
Doing a 2 DISTINCT queries will be expensive, so if you have a table of your groups and positions, I would suggest using those, rather than the CTEs:
WITH Groups AS
(SELECT DISTINCT
[group],
subgroup
FROM dbo.YourTable),
Positions AS
(SELECT DISTINCT
position
FROM dbo.YourTable)
SELECT G.[Group],
G.subgroup,
P.Position,
YT.[value]
FROM Groups G
CROSS JOIN Positions P
LEFT JOIN dbo.YourTable YT ON G.[Group] = YT.[Group]
AND G.subgroup = YT.subgroup
AND P.Position = YT.Position;

Answer 2

You seem to only want the value for the first "position" in each group. That suggests row_number():
select group, subgroup, position,
(case when row_number() over (partition by group, position order by subgroup) = 1
then value
end) as value
from t;
Here is a db<>fiddle.

Answer 3

Select distinct subgroups and positions first, then join them and outer join your table.
with sub as (select distinct group, subgroup from mytable)
, pos as (select distinct group, position from mytable)
select
sub.group. sub.subgroup, pos.position, t.value
from sub
join pos on pos.group = sub.group
left join mytable t on t.group = sub.group
and t.subgroup = sub.subgroup
and t.position = pos.position
order by t.group, t.subgroup, t.position;