Question

我有以下表格（缩写）

tableAssignments
    id
    timestamp             // updated when row is modified
    tableSystems
    tableUsers
    ...

tableAssignmentsSnapshot
    id
    timestamp             // set when row created, snapshots never change
    tableSystemsSnapshot
    tableUsersSnapshot
    tableAssignments_id   // reference to "tableAssignments" row this was created from
    syncKey               // Changed when snapshots are created, max value is latest

更改tableAssignments后的某个时间，将执行所有分配的快照，并使用相同的syncKey创建快照。我正在尝试编写一个查询来检查最新的“tableAssignmentsSnapshot”是否是最新的，或者是否应该采用新的。所需的逻辑是：

确定每个系统的最新tableAssignmentSnapshots，由最大syncKey确定（请参阅下面的查询）。
使用tableAssignments加入＃1的结果。
如果来自tableAssignments的时间戳＆gt; tableAssignmentsSnapshot的时间戳然后需要新的快照。

以下查询完成步骤＃1并快速运行。它返回tableAssignmentSnapshots，每个系统的最大值为“syncKey”。

select * from
    tableAssignmentsSnapshot d inner join tableSystemsSnapshot e
    on d.systemId = e.id
    where d.syncKey = (select MAX(syncKey) from tableAssignmentsSnapshot y inner join tableSystemsSnapshot z
  on y.systemId = z.id
   where tableSystems_id = e.tableSystems_id)

我正在努力做下一步该做什么。我需要能够执行以下操作，但遇到所需语法的问题：

select * from tableAssignments a right outer join
(
    the result from above query
)
on a.id = ?.tableAssignments_id

Answer 1

您可以将您的第一个查询包装在CTE上：

;WITH CTE AS
(
    SELECT * -- Here you should list only the columns that you are gonna need
    FROM tableAssignmentsSnapshot D
    INNER JOIN tableSystemsSnapshot E
        ON D.systemId = E.id
    WHERE D.syncKey = ( select MAX(syncKey) from tableAssignmentsSnapshot y inner join tableSystemsSnapshot z
                        on y.systemId = z.id
                        where tableSystems_id = e.tableSystems_id)
)

SELECT * 
FROM tableAssignments A
RIGHT JOIN CTE B
ON A.id = B.tableAssignments_id

如何为这个逻辑编写sql？

1 个答案: