Face Detection And Saving In Database Sql Server

This is not a good question as you don't specify which type of database you are using, nor do you specify any structure for the table you plan to store the image in.

You should have something like this

TableName: Persons
PersonID    FirstName    MiddleName    LastName   FaceImage
1           Johnny       B             Good       binary blob (or path to a file server)

Then you just use a SELECT statements to see if the person exists and if the column FaceImage is NULL or not

This is probably easiest to do in a stored procedure, because other wise you will a couple of extra transactions.

CREATE FUNCTION CheckImageExist(IN _firstName VARCHAR(45), IN _middleName VARCHAR(45), IN _lastName VARCHAR(45), IN _image BLOB)
RETURNS INT
BEGIN
    SELECT PersonID, NOT ISNULL(FaceImage) FROM Persons INTO @id, @imageExist
    WHERE FirstName = _firstName AND MiddleName = _middleName AND LastName = _lastName;
    IF ISNULL(@id) THEN -- The person doesn't exist
        INSERT INTO () VALUES (); -- This you can figure out yourself
    ELSEIF @imageExist = 1 THEN
        UPDATE Persons SET FaceImage = _image WHERE PersonID = @id;
    ELSE
        -- Here you could SIGNAL an error or do nothing 
    END IF;

    RETURN @imageExist;
END

In the above example I have used MySQL syntax, but it should be similar for other databases.
Also the syntax might not be 100% correct. It is more of a guidance to a solution.