sql-server - 选择脚本以包含另一个表的计数？

Question

我试图弄清楚如何编写脚本以从一个表中选择某些记录/字段，然后将其连接到另一个表并包含相应计数的列。例如，这就是我现在所拥有的：

select ID, Val from OriginalTable where Something = 1

现在我有另一个表，其中包含链接到该原始表的记录，其中 a列OriginalID与ID. OriginalTable一个例子是：

select * from OtherTable where OriginalID = 3

...其中 3 =ID的OriginalTable。

我想要做的是在第一个语句中添加一个列，该列显示另一个表的计数，如第二个查询中所示。例如，这可能是一个结果集：

ID    Val    Count
1     abc    15
2     def    23
3     ghi    42
4     jkl    19

如何编写此查询以包含此计数？

Answer 1

有很多方法可以做到这一点，但您可以使用Group By

select ID, Val, [Count] = count(1)
from OriginalTable be
left join OtherTable ot on be.OriginalID = ot.OriginalID
where Something = 1
group by ID,Val

或者你可以使用OVERand Partition By：

select ID, Val, [Count] = count(1) OVER(PARTITION BY ID,Val)
from OriginalTable be
left join OtherTable ot on be.OriginalID = ot.OriginalID
where Something = 1

我个人喜欢这种OVER方法。这里有 MSDN 上的信息。

Answer 2

子查询应该为您处理：

SELECT 
  ID, Val, Cnt
FROM OriginalTable
JOIN (
  SELECT 
    OriginalID, COUNT(*) AS Cnt
  FROM OtherTable
  GROUP BY OriginalID
  ) AS Sub ON ID=OriginalID

Answer 3

;WITH ot(ID, c) AS 
(
  SELECT OriginalID, COUNT(*)
   FROM dbo.OtherTable
   GROUP BY OriginalID
)
SELECT t.ID, t.Val, [Count] = COALESCE(ot.c, 0)
  FROM dbo.OriginalTable AS t
  LEFT OUTER JOIN ot
  ON t.ID = ot.ID
  WHERE t.Something = 1;

Answer 4

SELECT be.ID, be.Val, Count(*) AS [Count]
FROM OriginalTable be
LEFT OUTER JOIN OtherTable ot ON be.ID = ot.OriginalID
WHERE be.Something = 1
GROUP BY be.ID, be.Val