Question

I would like to use following sql to avoid constructing sql dynamically:

SELECT CommentID, Comment, 
FROM Comments
--if Author id is not null then filter upon author id otherwise get all comments (ignore author id)
WHERE AuthorID LIKE COALESCE(@AuthorId, '%') 
   --if comment type is present filter upon it, otherwise get all comments (ignore comment type condition)
   AND CommentType LIKE COALESCE(@CommentType, '%') 

I want to know is that safe way to approach this problem?

EDIT:
Here is final code that satisfy my need to ignore search parameter if is null and applied it if is present:

SELECT CommentID, Comment, 
FROM Comments
--if @AuthorId is not null then filter upon @AuthorId otherwise get all comments (ignore author id)
WHERE AuthorID = COALESCE(@AuthorId, AuthorID) 
    --if @CommentType is present filter upon it, otherwise get all comments (ignore comment type condition)
    AND CommentType = COALESCE(@CommentType, CommentType)  

Answer 1

If AuthorId or CommentType are nullable, this will not work. Instead you should use an OR:

SELECT CommentID, Comment, 
FROM Comments
WHERE ( @AuthorId Is Null Or AuthorId = @AuthorId )
    And ( @CommentType Is Null Or CommentType Like @CommentType )

Btw, if AuthorId and CommentType are not nullable, then you can use Coalesce like so:

SELECT CommentID, Comment, 
FROM Comments
WHERE AuthorId = Coalesce(@AuthorId, AuthorId)
    And CommentType = Coalesce(@CommentType, CommentType )

The catch is that this is an exact match as opposed to a wildcard match like you had with LIKE.