IF ISNULL(@LastName, '') <> '' or ISNULL(@FirstName, '') <> '' or ISNULL(@State, '') <> ''
BEGIN
-- Old way
    set @SQL = 'insert into SearchTable '
             + 'select top 100 AcctNum, ' + CAST(@Session AS VARCHAR(5)) 
             + ' from FromTable '
             + 'where 1 = 1 '
    if @LastName <> ''
        set @SQL = @SQL + ' and LName = ' + @Quote + @LastName + @Quote + ' '
    if @FirstName <> ''
        set @SQL = @SQL + ' and FName like ' + @Quote + '%' + @FirstName + '%' + @Quote + ' '
    if @State <> ''
        set @SQL = @SQL + ' and [State] = ' + @Quote + @State + @Quote + ' ';
    execute sp_executesql @SQL

-- Proposed way
    INSERT INTO SearchTable 
    SELECT TOP 100 AcctNum, @Session 
    FROM FromTable 
    WHERE 1 = 1 
        AND LNAME LIKE CASE WHEN ISNULL(@LastName , '') = '' THEN '%' ELSE @LastName END 
        AND FNAME LIKE CASE WHEN ISNULL(@FirstName, '') = '' THEN '%' ELSE '%' + @FirstName + '%' END 
        AND [STATE] LIKE CASE WHEN ISNULL(@State, '') = '' THEN '%' ELSE @State END; 
END --IF