RANK を使用してそれを行うには、RANK をサブクエリに追加し、CaseID と Agent ごとに DateEdited をランク付けしてから、メインクエリに WHERE 句を配置して、ランクが 1 の行のみを選択する必要があります。パーティション句を正しく取得しました-データが表示されないのは少し難しいです。
このような:
SELECT
[Case].CaseID
,Agent.AgentName
,Assignment.Description
,A.AgentName AS EditedBy
,A.DateEdited
FROM Agent
INNER JOIN [Case-Agent] ON [Case-Agent].AgentID = Agent.AgentID
INNER JOIN [Assignment] ON Assignment.AssignmentID = [Case-Agent].AssignmentID
INNER JOIN [Case] ON [Case].CaseID = [Case-Agent].CaseID
INNER JOIN (SELECT
EditedCase.CaseID
,[EditedCase].DateEdited
,[Agent].AgentName
,RANK ( ) OVER (PARTITION BY EditedCase.CaseID, [Agent].AgentName
ORDER BY [EditedCase].DateEdited DESC ) AS pos
FROM EditedCase
INNER JOIN [Agent] on [Agent].AgentID = [EditedCase].AgentID) A on A.CaseID = [Case].CaseID
WHERE [Assignment].AssignmentID = 0
AND pos = 1
次のように、サブクエリを集計クエリに変更して、MAX の日付を戻すこともできます。
SELECT
[Case].CaseID
,Agent.AgentName
,Assignment.Description
,A.AgentName AS EditedBy
,A.DateEdited
FROM Agent
INNER JOIN [Case-Agent] ON [Case-Agent].AgentID = Agent.AgentID
INNER JOIN [Assignment] ON Assignment.AssignmentID = [Case-Agent].AssignmentID
INNER JOIN [Case] ON [Case].CaseID = [Case-Agent].CaseID
INNER JOIN (SELECT
EditedCase.CaseID
,MAX([EditedCase].DateEdited) AS DateEdited
,[Agent].AgentName
FROM EditedCase
INNER JOIN [Agent] on [Agent].AgentID = [EditedCase].AgentID
GROUP BY
EditedCase.CaseID
,[Agent].AgentName) A on A.CaseID = [Case].CaseID
WHERE [Assignment].AssignmentID = 0
AND pos = 1