Question

I’m working on a SQL Server 2008 database. This database has two tables.

Book
ID
BookCategoryID
Name
IsFlagged

BookCategory
ID
Name
IsFlagged

I need to update the BookCategory table so that if any books in a category are flagged, the IsFlagged property on the BookCategory record is set to true. Otherwise, if there are not any books in a category that are flagged, I need to set the IsFlagged property on the BookCategory record to false. Is there a way to do this? I can’t seem to figure it out. I was trying something like the following but kept hitting a dead-end.

UPDATE
  BookCategory
SET
  IsFlagged = (SELECT COUNT(*) FROM Book WHERE [IsFlagged]=1 AND [BookCategory]=?)

Answer 1

UPDATE bc
SET IsFlagged = CASE WHEN b.ID IS NULL THEN 0 ELSE 1 END
FROM
    BookCategory bc LEFT JOIN
    Book b ON b.BookCategoryID = bc.ID AND b.IsFlagged = 1