Just trying to figure out the best way to design my table for the following scenario:

I have several areas in my system (documents, projects, groups and clients) and each of these can have comments logged against them.

My question is should I have one table like this:

```
CommentID
DocumentID
ProjectID
GroupID
ClientID
etc

```

Where only one of the ids will have data and the rest will be NULL or should I have a separate CommentType table and have my comments table like this:

```
CommentID
CommentTypeID
ResourceID (this being the id of the project/doc/client)
etc

```

My thoughts are that option 2 would be more efficient from an indexing point of view. Is this correct?