Backport of the patch for bug #8457 "Precision math: DIV

returns incorrect result with large decimal value" 
 
For the DIV operator, neither operands nor result were checked 
for integer overflows. 
 
This patch changes the DIV behavior for non-integer operands as 
follows: if either of the operands has a non-integer type, 
convert both operands to the DECIMAL type, then calculate the 
division using DECIMAL arithmetics. Convert the resulting 
DECIMAL value into BIGINT [UNSIGNED] if it fits into the 
corresponding range, or throw an 'out of range' error 
otherwise. 

mysql-test/r/func_math.result:
  Added a test case for bug #8457.
  Fixed results for a test case depending on the wrong behavior.
mysql-test/r/type_varchar.result:
  Fixed results for a test case depending on the wrong behavior.
mysql-test/t/func_math.test:
  Added a test case for bug #8457.
sql/item_func.cc:
  If either of the operands has a non-integer type, convert both 
  operands to the DECIMAL type, then calculate the division using 
  DECIMAL arithmetics. Convert the resulting DECIMAL value into 
  BIGINT [UNSIGNED] if it fits into the corresponding range, or 
  throw an 'out of range' error otherwise.

1 files changed, 32 insertions, 0 deletions

diff --git a/sql/item_func.cc b/sql/item_func.cc
index cf499aaf93c..c0a84e3be28 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -1348,6 +1348,38 @@ void Item_func_div::fix_length_and_dec()
 longlong Item_func_int_div::val_int()
 {
   DBUG_ASSERT(fixed == 1);
+
+  /*
+    Perform division using DECIMAL math if either of the operands has a
+    non-integer type
+  */
+  if (args[0]->result_type() != INT_RESULT ||
+      args[1]->result_type() != INT_RESULT)
+  {
+    my_decimal value0, value1, tmp;
+    my_decimal *val0, *val1;
+    longlong res;
+    int err;
+
+    val0= args[0]->val_decimal(&value0);
+    val1= args[1]->val_decimal(&value1);
+    if ((null_value= (args[0]->null_value || args[1]->null_value)))
+      return 0;
+
+    if ((err= my_decimal_div(E_DEC_FATAL_ERROR & ~E_DEC_DIV_ZERO, &tmp,
+                             val0, val1, 0)) > 3)
+    {
+      if (err == E_DEC_DIV_ZERO)
+        signal_divide_by_null();
+      return 0;
+    }
+
+    if (my_decimal2int(E_DEC_FATAL_ERROR, &tmp, unsigned_flag, &res) &
+        E_DEC_OVERFLOW)
+      my_error(ER_WARN_DATA_OUT_OF_RANGE, MYF(0), name, 1);
+    return res;
+  }
+  
   longlong value=args[0]->val_int();
   longlong val2=args[1]->val_int();
   if ((null_value= (args[0]->null_value || args[1]->null_value)))