SQL Need to check if null or empty string and another condition - query not working

sorry maybe I wasn't clear.  I don't want null values in the history table unless it's at least the second record in histroy.  Meaning they had inserted text previously and then blanked it out.  Am I understanding correctly that your first one inserts null values if there is no record and they inserted a null value.  If @Detail is null.  I need to check if there is already a record in Appraisal History with this ID.  If there is, I need to insert the blank record to history, otherwise I don't want a blank record in History.

I reveresed them from your original.  The 2nd one takes care of that.
if detail has something and an appraisal id exists but with null or blank detail insert a blank record.

the top one is if detail is empty or null and an id exists insert a blank.

sorry, typo, change the top one
WHERE AppraisalResponseID = @AppraisalResponseID) =0
shoudl be
WHERE AppraisalResponseID = @AppraisalResponseID) >0

now I see the confusion.  Basically, what I am doing is copying whats in the Appraisal Table to the History Table.  I start out with a blank record in the table.  I only want to copy that blank record to the history table if it is intentional, meaning that someone had text and then deleted it.  

So if there is a record in history already (meaning they had text in previously) copy the blank record that's in the Appraisal table to History.  So the insert should still be

SELECT AppraisalResponse.ID,
                  AppraisalResponse.PermissionID,
                   AppraisalResponse.AppraisalTypeQuestionPromptID,
                   AppraisalResponse.Detail,
                  AppraisalResponse.ModifiedDate,
                  PersonID
            FROM AppraisalResponse
            WHERE AppraisalResponse.ID=@AppraisalResponseID AND AppraisalResponse.Detail<>@Detail

becuase we are not inserting unless there is a difference between what's in there now and the new @Detail (which might be blank).

Does this make it more clear?

How's this?  I put them back in your original order.

IF @Detail is not null AND LEN(@Detail) > 0
      AND (SELECT
            COUNT(AppraisalResponseID)
            FROM AppraisalResponseHistory
            WHERE AppraisalResponseID = @AppraisalResponseID AND (Detail is null or LEN(Detail) > 0)) >0
      BEGIN
            INSERT INTO AppraisalResponseHistory
            ( AppraisalResponseID,
                  PermissionID,
                  AppraisalTypeQuestionPromptID,
                  Detail,
                  ModifiedDate,
                  PersonID )
     
            SELECT AppraisalResponse.ID,
                  AppraisalResponse.PermissionID,
                   AppraisalResponse.AppraisalTypeQuestionPromptID,
                   AppraisalResponse.Detail,
                  AppraisalResponse.ModifiedDate,
                  PersonID
            FROM AppraisalResponse
            WHERE AppraisalResponse.ID=@AppraisalResponseID AND AppraisalResponse.Detail<>@Detail
     
      END

IF @Detail is null OR LEN(@Detail) = 0
      AND (SELECT
            COUNT(AppraisalResponseID)
            FROM AppraisalResponseHistory
            WHERE AppraisalResponseID = @AppraisalResponseID) >0
      BEGIN
            INSERT INTO AppraisalResponseHistory
            ( AppraisalResponseID,
                  PermissionID,
                  AppraisalTypeQuestionPromptID,
                  Detail,
                  ModifiedDate,
                  PersonID )
     
            SELECT AppraisalResponse.ID,
                  AppraisalResponse.PermissionID,
                   AppraisalResponse.AppraisalTypeQuestionPromptID,
                   AppraisalResponse.Detail,
                  AppraisalResponse.ModifiedDate,
                  PersonID
            FROM AppraisalResponse
            WHERE AppraisalResponse.ID=@AppraisalResponseID AND AppraisalResponse.Detail<>@Detail

END

thank that looks good.  But, I just want to double check.  The first one

IF @Detail is not null AND LEN(@Detail) > 0
      AND (SELECT
            COUNT(AppraisalResponseID)
            FROM AppraisalResponseHistory
            WHERE AppraisalResponseID = @AppraisalResponseID AND (Detail is null or LEN(Detail) > 0)) >0

this says @detail has some sort of string and there is a corresponding record already in Appraisal response history, then it should do the history update.  Why do we need the AND (Detail is null or LEN(Detail) > 0)) >0.  

that's to satisfy your statement in the original post
"I need to check if AppraisalResponse.Detail is blank or null (- I think this is where I am running into so much trouble).  If it is blank or null then I need to check if there is already a record in AppraisalHistory with this ID"

so, Detail is checking AppraisalResponse.Detail not blank.  Right, I need to check if it's null and then only do it if the Count in History is GT 0.  So does that do that?  Thanks so much.

it looks like it's looking at History.Detail and not AppraisalResponse.Detail to check if the last record is blank.  I specifically need it to look at the other table.