使用WITH子句的结果执行JOIN

Question

我有一个已经使用一个联接的查询，将其称为query1。我想将query1加入WITH子句的结果中。我不知道如何合并两个数据集。

查询1：

SELECT 
    p.NetObjectID, 
n.Caption, n.ObjectSubType
FROM Pollers p
  LEFT JOIN NodesData n 
    ON n.NodeID = p.NetObjectID

下一个查询是WITH子句。我不知道如何在不使用WITH的情况下获得结果，因为我需要执行this post中概述的操作。

查询2：

WITH ranked_DateStamp AS 
        (
        SELECT c.NodeID, c.DateTime, ROW_NUMBER() OVER (PARTITION BY NodeID ORDER BY DateTime DESC) AS rn
        FROM CPULoad AS c
        )
SELECT * FROM ranked_DateStamp WHERE rn = 1;

我以为我可以将rank_DateStamp加入JOIN_DateStamp.NodeID = p.NodeID，但不允许这样做。

Answer 1

您不需要真正在这里需要with子句，可以使用子查询。我只是这样说：

SELECT 
    p.NetObjectID, 
    n.Caption, 
    n.ObjectSubType,
    c.DateTime
FROM Pollers p
LEFT JOIN NodesData n ON n.NodeID = p.NetObjectID
LEFT JOIN (
    SELECT 
        c.NodeID, 
        c.DateTime, 
        ROW_NUMBER() OVER (PARTITION BY NodeID ORDER BY DateTime DESC) AS rn
    FROM CPULoad AS c
) c ON c.rn = 1 and c.NodeID = p.NetObjectID

但是，如果要使用公用表表达式，则看起来像：

WITH ranked_DateStamp AS (
    SELECT 
        c.NodeID, 
        c.DateTime, 
        ROW_NUMBER() OVER (PARTITION BY NodeID ORDER BY DateTime DESC) AS rn
    FROM CPULoad AS c
)
SELECT 
    p.NetObjectID, 
    n.Caption, 
    n.ObjectSubType,
    c.DateTime
FROM Pollers p
LEFT JOIN NodesData n ON n.NodeID = p.NetObjectID
LEFT JOIN ranked_DateStamp c ON c.rn = 1 and c.NodeID = p.NetObjectID