Fix calculation of TIMESTAMPDIFF() of months and years. (Bug #13534)

mysql-test/r/func_time.result:
  Add new results
mysql-test/t/func_time.test:
  Add new regression test
sql/item_timefunc.cc:
  Fix calculation of years and months in TIMESTAMPDIFF().

1 files changed, 21 insertions, 42 deletions

diff --git a/sql/item_timefunc.cc b/sql/item_timefunc.cc
index 7f94c19647e..459b5a22cb1 100644
--- a/sql/item_timefunc.cc
+++ b/sql/item_timefunc.cc
@@ -2723,16 +2723,16 @@ longlong Item_func_timestamp_diff::val_int()
       int_type == INTERVAL_QUARTER ||
       int_type == INTERVAL_MONTH)
   {
-    uint year;
-    uint year_beg, year_end, month_beg, month_end;
-    uint diff_days= (uint) (seconds/86400L);
-    uint diff_years= 0;
+    uint year_beg, year_end, month_beg, month_end, day_beg, day_end;
+    uint years= 0;
     if (neg == -1)
     {
       year_beg= ltime2.year;
       year_end= ltime1.year;
       month_beg= ltime2.month;
       month_end= ltime1.month;
+      day_beg= ltime2.day;
+      day_end= ltime1.day;
     }
     else
     {
@@ -2740,53 +2740,32 @@ longlong Item_func_timestamp_diff::val_int()
       year_end= ltime2.year;
       month_beg= ltime1.month;
       month_end= ltime2.month;
-    }
-    /* calc years*/
-    for (year= year_beg;year < year_end; year++)
-    {
-      uint days=calc_days_in_year(year);
-      if (days > diff_days)
-	break;
-      diff_days-= days;
-      diff_years++;
+      day_beg= ltime1.day;
+      day_end= ltime2.day;
     }
 
-    /* calc months;  Current year is in the 'year' variable */
-    month_beg--;	/* Change months to be 0-11 for easier calculation */
-    month_end--;
+    /* calc years */
+    years= year_end - year_beg;
+    if (month_end < month_beg || (month_end == month_beg && day_end < day_beg))
+      years-= 1;
 
-    months= 12*diff_years;
-    while (month_beg != month_end)
-    {
-      uint m_days= (uint) days_in_month[month_beg];
-      if (month_beg == 1)
-      {
-	/* This is only calculated once so there is no reason to cache it*/
-	uint leap= (uint) ((year & 3) == 0 && (year%100 ||
-					       (year%400 == 0 && year)));
-	m_days+= leap;
-      }
-      if (m_days > diff_days)
-	break;
-      diff_days-= m_days;
-      months++;
-      if (month_beg++ == 11)		/* if we wrap to next year */
-      {
-	month_beg= 0;
-	year++;
-      }
-    }
-    if (neg == -1)
-      months= -months;
+    /* calc months */
+    months= 12*years;
+    if (month_end < month_beg || (month_end == month_beg && day_end < day_beg))
+      months+= 12 - (month_beg - month_end);
+    else
+      months+= (month_end - month_beg);
+    if (day_end < day_beg)
+      months-= 1;
   }
 
   switch (int_type) {
   case INTERVAL_YEAR:
-    return months/12;
+    return months/12*neg;
   case INTERVAL_QUARTER:
-    return months/3;
+    return months/3*neg;
   case INTERVAL_MONTH:
-    return months;
+    return months*neg;
   case INTERVAL_WEEK:          
     return seconds/86400L/7L*neg;
   case INTERVAL_DAY: