sql - Create Computed Column using data from another table

Question

I have a SQL Server 2008 R2 database. This database has two tables called Pictures and PictureUse.

Picture table has the following columns:

Id (int)   
PictureName (nvarchar(max)) 
CreateDate (datetime )  

PictureUse table has the following columns :

Id (int) 
Pictureid (int) 
CreateDate (datetime )  

I need to create a computed column in the Picture table which tells me that how many times this picture has been clicked.any help ?

Answer 1

You can create a user-defined function for that:

CREATE FUNCTION dbo.CountUses(@pictureId INT)
RETURNS INT
AS
  BEGIN
      RETURN
        (SELECT Count(id)
         FROM   PictureUse
         WHERE  PictureId = @PictureId)
  END 

The computed column can then be added like this:

ALTER TABLE dbo.Picture
ADD NofUses AS dbo.CountUses(Id)

However, I would rather make a view for this:

CREATE VIEW PictureView
AS
  SELECT Picture.Id,
         PictureName,
         Picture.CreateDate,
         Count(PictureUse.Id) NofUses
  FROM   Picture
         JOIN PictureUse
           ON Picture.Id = PictureUse.PictureId
  GROUP  BY Picture.Id,
            PictureName,
            Picture.CreateDate