btr0cur.c:

  Do not add + 1 to the InnoDB index cardinality estimate if the B-tree just contains one page; the fix made in March 2004 caused InnoDB systematically to overestimate the cardinality of empty or small tables by 1

innobase/btr/btr0cur.c

@@ -2707,8 +2707,11 @@ btr_estimate_number_of_different_key_vals(
 			rec = page_rec_get_next(rec);
 		}
 		
+
 		if (n_cols == dict_index_get_n_unique_in_tree(index)) {
-			/* We add one because we know that the first record
+
+			/* If there is more than one leaf page in the tree,
+			we add one because we know that the first record
 			on the page certainly had a different prefix than the
 			last record on the previous index page in the
 			alphabetical order. Before this fix, if there was
@@ -2716,8 +2719,12 @@ btr_estimate_number_of_different_key_vals(
 			algorithm grossly underestimated the number of rows
 			in the table. */
 
+			if (btr_page_get_prev(page, &mtr) != FIL_NULL
+			    || btr_page_get_next(page, &mtr) != FIL_NULL) {
+
 				n_diff[n_cols]++;
 			}
+		}
 
 		total_external_size +=
 				btr_rec_get_externally_stored_len(rec);