Question

这似乎是SQL中的一个基本操作，但它让我感到难过。

我有大约2个不同的子查询，每个子查询按LOCATION_ID分组，包含日期列。例如，一个查询包括WORKORDER个记录的列表，而另一个查询从NOTE表中提取记录。这两个查询都包含LOCATION表的联接，允许我按LOCATION_ID进行分组。

我的目标是在该特定位置提取最新联系日期，并且可以采用存储在不同表格中的工作单，备注日期，后续日期等形式。理想情况下，我会按LOCATION_ID分组查询，显示该位置的最新联系日期。

我会发布SQL但我没有任何目前正在为我工作的东西。关于如何处理这种情况的任何想法？

谢谢！

SELECT 
   L.LOCATION_ID, Max(MaxDate) 
FROM 
   LOCATION AS L
LEFT JOIN 
   (SELECT 
       LOCATION_ID, Max(dbo.LeadNote.NoteDate) AS MaxDate 
    FROM 
       LeadNote 
    INNER JOIN 
       LOCATION ON LeadNote.LOCATION_ID = LOCATION.LOCATION_ID 
    GROUP BY 
       LOCATION_ID) T1 ON L.LOCATION_ID = T1.CONTACTLOCATION_LOCATION_ID
LEFT JOIN 
   (SELECT 
       LOCATION_ID, Max(dbo.WORKORDER.WORKORDER_DATECREATED) AS MaxDate 
    FROM 
       WORKORDER 
    INNER JOIN 
       LOCATION ON LOCATION_ID = WORKORDER_LOCATION_ID 
    GROUP BY 
       LOCATION_ID) T2 ON L.LOCATION_ID = T2.CONTACTLOCATION_LOCATION_ID`

Answer 1

也许您可以尝试使用UNION获取单个sql结果，然后将其包装并为其赋予别名，然后在您希望的字段上应用MAX，两个查询都返回。请记住，要使用UNION，两个查询都必须返回相同的字段名称集。

例如：

Query A:

   Select a, b, c from T1 where....

Query B:
   Select a, f, e from T2 where...


you would have:

  SELECT MAX(e)
  FROM
    ( 
     (Select a, b, c, NULL as f, NULL as e from T1 where....)
     UNION
     (Select a, NULL as b, NULL as c, f, e from T2 where...)
    ) t

Answer 2

如果您需要使用连接，可以使用case语句来获取更大的日期。

SELECT
   L.LOCATION_ID,
   (CASE WHEN(T2.MaxDate IS NULL OR T1.MaxDate > T2.MaxDate)
   THEN T1.MaxDate
   ELSE T2.MaxDate
   END) MaxDate
...

Answer 3

尝试：

SELECT 
   L.LOCATION_ID, Max(MaxDate) 
FROM 
(
   (
    SELECT 
        LOCATION_ID, Max(LeadNote.NoteDate) AS MaxDate 
    FROM 
        LeadNote 
    JOIN 
        LOCATION 
    ON 
        LeadNote.LOCATION_ID = LOCATION.LOCATION_ID 
    GROUP BY 
        LOCATION_ID
   )
UNION 
   (
    SELECT 
       LOCATION_ID, Max(WORKORDER.WORKORDER_DATECREATED) AS MaxDate 
    FROM 
       WORKORDER 
    JOIN 
       LOCATION ON LOCATION_ID = WORKORDER_LOCATION_ID 
    GROUP BY 
       LOCATION_ID
   )
)

可能需要稍微调整......但是如果有效的话，可以通过@DrCopyPaste对评论表示赞赏：）

Answer 4

您可以使用简单的连接和案例陈述来执行此操作：

SELECT 
   L.LOCATION_ID, 
   CASE WHEN(Max(LeadNote.NoteDate) IS NULL OR Max(LeadNote.NoteDate) > Max(WORKORDER.WORKORDER_DATECREATED) 
     THEN Max(LeadNote.NoteDate) 
     ELSE Max(WORKORDER.WORKORDER_DATECREATED) end AS maxDate
FROM 
   LOCATION AS L
LEFT JOIN LeadNote ON LeadNote.LOCATION_ID = LOCATION.LOCATION_ID 
LEFT JOIN WORKORDER ON L.LOCATION_ID = WORKORDER_LOCATION_ID 
GROUP BY L.LOCATION_ID

跨两个或更多查询的SQL MAX（）值

4 个答案: