Already approved bug fix for #1561.

Bug happens in INTERVAL function when number of compared arguments
is 8 or more.

mysql-test/r/func_set.result

@@ -50,3 +50,9 @@ id	elt(two.val,'one','two')
 2	one
 4	two
 drop table t1,t2;
+SELECT INTERVAL(13, 7, 14, 21, 28, 35, 42, 49, 56);
+INTERVAL(13, 7, 14, 21, 28, 35, 42, 49, 56)
+1
+SELECT INTERVAL(13, 7, 14, 21, 28, 35, 42, 49, 56, 77);
+INTERVAL(13, 7, 14, 21, 28, 35, 42, 49, 56, 77)
+1

mysql-test/t/func_set.test

@@ -35,3 +35,8 @@ insert into t2 values (1,1),(2,1),(3,1),(4,2);
 select one.id, elt(two.val,'one','two') from t1 one, t2 two where two.id=one.id;
 select one.id, elt(two.val,'one','two') from t1 one, t2 two where two.id=one.id order by one.id;
 drop table t1,t2;
+
+# some more INTERVAL tests 
+
+SELECT INTERVAL(13, 7, 14, 21, 28, 35, 42, 49, 56);
+SELECT INTERVAL(13, 7, 14, 21, 28, 35, 42, 49, 56, 77);

sql/item_cmpfunc.cc

@@ -603,7 +603,7 @@ longlong Item_func_interval::val_int()
   if (intervals)
   {					// Use binary search to find interval
     uint start,end;
-    start= 1;
+    start= 0;
     end=   row->cols()-2;
     while (start != end)
     {