从另一个表中的数据更新计数列

Question

在我的数据库中我有两个表项(Id,...,ToatlViews int)和ItemViews(id,ItemId,Timestamp)

在ItemViews表中,我存储项目进入站点时的所有视图.我不时想调用存储过程来更新Items.ToatlViews字段.我尝试使用游标执行此SP ...但更新语句错误.你能帮我纠正一下吗？没有光标我可以这样做吗？

CREATE PROCEDURE UpdateItemsViews
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    DECLARE @currentItemId int
    DECLARE @currentItemCursor CURSOR
    SET @currentItemCursor = CURSOR FOR SELECT Id FROM dbo.Items

    OPEN @currentItemCursor
    FETCH NEXT FROM @currentItemCursor INTO @currentItemId
    WHILE @@FETCH_STATUS = 0
    BEGIN
        Update dbo.Items set TotalViews = count(*) 
              from dbo.ItemViews where ItemId=@currentItemId
        FETCH NEXT FROM @currentItemCursor INTO @currentItemId
    END   
END
GO

Answer 1

您可以使用直接UPDATE语句

update Items set TotalViews = 
     (select COUNT(id) from ItemViews where ItemViews.ItemId = Items.Id)

如果这很重要,您可能希望以各种方式测试性能.

Answer 2

您可以使用update ... from而不是游标:

update  i
set     TotalViews = iv.cnt
from    dbo.Item i
join    (
        select  ItemId
        ,       count(*) as cnt
        from    dbo.ItemViews
        group by
                ItemId
        ) iv
on      i.Id = iv.ItemId