Select distinct on foreign key, inner join another table - sql

Question

Basically what I want to do is, select the 3 last actions made from the user. But no duplicates on RelationId, and also innerjoin permissions just to make sure the user has permission still to make the same action.
The only thing I want from permission is RelationId.
By no duplicated I mean if there is two rows of Action with the same RelationId the one closes to the top ( Ordered by TimeStamp ) should be picked.
What I've came up with so far:
SELECT DISTINCT a.*, p.RelationId
FROM [Action] [a]
INNER JOIN [Permission] p
ON ([p].[RelationId] = [a].[RelationId]
AND [p].[RelationType] = [a].[RelationType]
AND [p].[UserId] = [a].[UserId]
AND [p].[Deleted] = 0)
WHERE [a].[ActionType] = 'Clicked'
AND [a].[RelationType] = 'Direct'
AND [a].[UserId] = 5
AND [a].[Deleted] = 0
ORDER BY [a].[TimeStamp] DESC
OFFSET 0 ROWS
FETCH NEXT 3 ROWS ONLY
It need to use OFFSET X ROWS and FETCH NEXT 3 ROWS ONLY for paging
This doesn't work for some reason, because I get duplicates on RelationId.
No errors.
example data:
action (
id INTEGER PRIMARY KEY,
ActionType VARCHAR(50) not null,
RelationId INTEGER ForeignKey,
Deleted Bit not null,
TimeStamp DATE not null,
UserId INTEGER ForeignKey
);
Desired result: 3 last actions made by one user that has permissions for it distinct by RelationId.

Answer 1

From your definition of last 3 per user (if last 3 then it can't be a single row per relationId):
with data as (
SELECT *,
row_number() over (partition by relationId order by [timeStamp] desc) as rNo
from action
where [ActionType] = 'Clicked' AND
[RelationType] = 'Direct' AND
[UserId] = 5 AND
[Deleted] = 0
)
select a.id,a.ActionType,a.RelationId,a.Deleted,a.TimeStamp,a.UserId,
p.RelationId as pRelId
FROM [data] [a]
INNER JOIN [Permission] p ON ([p].[RelationId] = [a].[RelationId] AND [p].[RelationType] = [a].[RelationType] AND [p].[UserId] = [a].[UserId])
WHERE p.[Deleted] = 0 and a.rNo <= 3
ORDER BY [a].[TimeStamp] DESC;

Answer 2

If I get it, you need for each Permission only the latest action, and from all these keep most recent three rows. Here:
select top 3 p.RelationId,top_action.*
from
[Permission] p
cross apply
(
select top 1 *
from [Action] [a]
where
[p].[RelationId] = [a].[RelationId] AND [p].[RelationType] = [a].[RelationType] AND [p].[UserId] = [a].[UserId]
and [a].[ActionType] = 'Clicked' AND [a].[RelationType] = 'Direct' AND [a].[UserId] = 5 AND [a].[Deleted] = 0
order by [a].[TimeStamp] DESC
)top_action
where [p].[Deleted] = 0
order by top_action.[TimeStamp] DESC

Answer 3

Distinct will always distinct all parameters. Selecting * will always differ.
You need to choose just one parameter to determine.
You can use group by, or simply make it in two steps using same select. Like this:
select * from Action where id in (
SELECT DISTINCT a.id
FROM [Action] [a]
INNER JOIN [Permission] p
ON ([p].[RelationId] = [a].[RelationId]
AND [p].[RelationType] = [a].[RelationType]
AND [p].[UserId] = [a].[UserId]
AND [p].[Deleted] = 0)
WHERE [a].[ActionType] = 'Clicked'
AND [a].[RelationType] = 'Direct'
AND [a].[UserId] = 5
AND [a].[Deleted] = 0
ORDER BY [a].[TimeStamp] DESC
OFFSET 0 ROWS
FETCH NEXT 3 ROWS ONLY
)

Answer 4

Solved it by doing this. Don't know if its the best solution though.
SELECT [a].*, [p].[Id]
FROM (SELECT *, ROW_NUMBER() OVER(PARTITION BY [RelationId] ORDER BY [TimeStamp] DESC) AS row from [Action]) a
INNER JOIN [Permission] p ON ([ep].[RelationId] = [a].[RelationId] AND [p].[RelationType] = [a].[RelationType] AND [p].[UserId] = [a].[UserId] AND [p].[Deleted] = 0)
WHERE row = 1 AND [a].[ActionType] = 'Clicked' AND [a].[RelationType] = 'Direct' AND [a].[UserId] = 5 AND [a].[Deleted] = 0
ORDER BY [a].[TimeStamp] DESC
OFFSET 0 ROWS
FETCH NEXT 3 ROWS ONLY